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Hi Everyone,

 

It’s been 2 months now of researching, reading every thread I can, trying, monitoring with no success; I am now totally stuck and don’t see what else I can do to solve my issue, and this is driving me mad ^^ !

 

I have a Subaru Impreza Hatchback 1998, EJ15 GF1, manual, petrol, with now 190,000 km. Small engine, pretty well maintained, I change all filters and oil every 10k since I have it, the previous owner was taking care of it and I bought it after the cam belt and water pump were changed professionally by a garage., around 170k.

 

So one day (around 187k) I noticed the car smelled a bit like overheating engine. I checked under the bonnet and noticed that the fans were not working. After more in depth checking I noticed that the lower radiator hose was cold and there was no pressure in the radiator.

 

So bought a new thermostat and gasket (original Subaru) and new coolant, tried it with the new one and didn’t change a thing, the damn thing stays closed. Tested both thermostats in hot water, they both work fine.

I then tried to run the car without the thermostat, I get good pressure, the coolant is flowing, I could properly burp the cooling system and I could see the radiator was not clogged, but surprisingly the fans still did not turn on. So I bought new temperature sensor and sender and tried again, but nothing changed, the fans don’t turn on. I checked all the fuses, under the steering wheel and under the bonnet, tested the relays with the test wires under the steering wheel and both relays and fans work fine. (I also bypassed the relays with fuses and this turns on the fans, no problem).

 

The very weird thing is that when the thermostat is installed and the engine running, the temperature gauge comes up to the optimal position, slightly below the middle, and stays there, even though the engine keeps heating. I don’t have an infrared thermometer but I can tell by the smell and the heat, and the fact then the thermostat stays closed and fans stay off, that something is wrong and that the engine is too hot. It really smells like overheating engine and the hoses and engine are reeeeally hot.

Before this began happening, when it worked well, the fans turned on and off automatically and I could tell when the thermostat opened and closed, it was all fine.

 

I tested all sensors, new and old, with a multimeter and they all work fine, even the thermostats in hot water both open and close correctly.

I contacted a mechanic friend who checked everything, he used a pretty strong product to clean the cooling system in case there would be some kind of stop-leak or stuff clogging the system, but nothing, the circuit is clean. I even used a thin brush to try to clean possible depot around the sensor areas, but nothing came out, all is clean… I also cleaned the cooling system with my garden hose, I know it's not recommended but I was out of options, I confirm that water flows through everything and came out clean. (I rinsed with demineralised water several times after this and put new coolant).

 

I feel like I did everything I could, I don’t see what else to do. I am not sure this could be related, but (I think) this began happening the same month that someone tried to steal it, or at least I noticed this cooling issue like a month after. No big issue from these unskilled robbers, who just broke the door handle and damaged the ignition, but it took me like 2 weeks to fix this, but during this time I removed the battery from the car because I could not close it and I don’t have a garage. So the car stayed quite a long time without a battery. I thought this could have done something to the ECU (I have nearly no knowledge about this part of cars) but anyways, this should not impact the thermostat which is a purely mechanic part.  

 

So Guys, I don’t knot what else I can do. I am pretty sure that the radiator is fine, I have been driving without a thermostat since, the engine takes longer to heat and the temperature tends to decrease at high speed and increase at idle and low speeds (no fans working, remember) which seem logical to me. Also the heater core seems fine, heat turns on and off, no problem.

If you have any idea what might be going on I’d be super keen hearing your opinion, this is getting so frustrating.

 

Cheers guys, thanks for reading !

 

Oh and it's not a head gasket by the way, already checked, oil and coolant are fine, I changed both.

Edited by quentindc
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I'm going to start with the stupid, easy to overlook stuff. I do this to myself, so don't be insulted.

Have you checked your fans to see if they're plugged in?

Are the wires broken or cut to the fan?

Have to checked your hoses to make sure they're not collapsing while under load/suction?

Did you replace your radiator cap?

Did you replace your water pump on your last timing belt change?

Did you make sure your coolant isn't disappearing?

Does the coolant level in your overflow tank fluctuate dramatically between hot and cold operation? Beyond the normal range indicated on the reservoir.

Have you tried filling up the coolant system by filling the block then the radiator?

Are you using the right mixture of coolant to water?

Did you lose a rag when you were doing any of this work on it?

 

Questions to ponder.

 

Twitch

Edited by Twitch de la Brat

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Hey guys,

 

So to answer your questions:

 

Twitch:

 

I'm going to start with the stupid, easy to overlook stuff. I do this to myself, so don't be insulted. Not at all, thanks ;)
Have you checked your fans to see if they're plugged in? Yes, they work fine when testing relays
Are the wires broken or cut to the fan? No they are intact
Have to checked your hoses to make sure they're not collapsing while under load/suction? THey are fine even under pressure, the coolant flows well without thermostat
Did you replace your radiator cap? Yes
Did you replace your water pump on your last timing belt change? Yes, 20,000 km ago
Did you make sure your coolant isn't disappearing? Yes there is no leak anywhere, even after driving for long
Does the coolant level in your overflow tank fluctuate dramatically between hot and cold operation? Beyond the normal range indicated on the reservoir. When driving without thermostat, fluctuates normally, when thermostat on, doesn't fluctuate at all as Stat stays closed
Have you tried filling up the coolant system by filling the block then the radiator? No, haven't tried this, but coolant goes through everything I checked
Are you using the right mixture of coolant to water? Yup, followed the constructor manual
Did you lose a rag when you were doing any of this work on it? Good one : D but no I have all my rags

Forester:

 

Have you checked the fuse(s) and relay(s) that feed the fans? Yes, I checked everything, the fuses are good, and the relays are good too (used the test wires under dash to test them, they all click and activate the fans when tested).

Edited by quentindc

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Thanks Twitch,

 

I checked all hoses with and without thermostat, no ccollapse :/ . With thermostat in the bottom hose stays cold and top one super hot, and there is no pressure in the radiator.

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Just a thought--do you have a proper Subaru t-stat or a cheapie parts store one?  Have you tested it in a pot of boiling water?

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Is the thermostat being installed correctly? The spring section should be on the engine side of where the thermostat is mounted. You have to actually mount the thermostat upside down in its position in Subaru EJ engines ;)

 

Cheers

 

Bennie

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Yes I bought an original Subaru one, tested in hot water it works fine. ANd yes I put it in the right way, it does not fit the otherway anyways ;)

Plus i has such a hard time removing the other one i remember i had to pull on the upper part, and the spring section was up in the engine.

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How did you check the head gaskets?

 

When mine went, there was no mixing of coolant or oil in either systems. EJ HGs can weep lightly for a period of time before they let to and become an issue. I believe mine were doing this for some time before running the engine hot but not straight to the red unless I was in really slow traffic on a warming/hot day. I drove it for two days like this before the engine was stripped down.

 

If you suspect the HGs, just do them, especially if they've not been done before ;)

 

Cheers

 

Bennie

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It has nothing to do with the ECU.

 

Clogged exhaust or catalytic converter?

 

When it’s overheating does the cabin heat blow cold?

 

What kind of daily temps are you seeing, what country and flat easy driving or mountainous dirt road climbs?

 

I would get the temp gauge working properly. Replace sensor and swap in another instrument cluster (which is really easy just get a used one). Or pull and inspect yours to see if you can repair it. Or get an aftermarket gauge while you figure this out. Either way Get some real data.

 

Blown headgasket. If they’re not blown yet they’re going to driving while overheating. Every engine ever made blows headgaskets if it’s driven hot.

 

Oil and coolant DO NOT mix on that engine, or if they do then the condition is so bad you know what the issue is without needing to check. When it’s overheating it’ll push exhaust gases into the coolant and the pump cavitates.

To verify find a shop with a $$$$$ has analyzer and they can detect gases i the coolant.

 

 

Or Something is clogging the coolant flow. You seem confident this isn’t the issue. But I’d check the radiator. How do you know it’s flowing enough?

 

Or I’d pull the water pump and inspect it. They dont really fail on that engine but at this point you need to verify it can properly move sufficient fluid.

 

Pretty simple - clogged, pump or headgaskets. That’s it.

 

It seems odd to me that the gauge goes to the right position like it working but you think it’s overheating.

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I just have 2-3 oddball things to contribute

 

I think that car has 2 temp sensors, one for the gauge only, the other is for the ECU - did the correct one get changed? (it's possible it has newer style with both sensors in one unit)

 

 

I wonder if the heater core is clogged? The circuit that flows through is needed so the t'stat works correctly. As a test, you can bypass the heater core and loop the 2 hoses together

 

 

is the 'jiggle pin' in the t'stat at the top (12 o'clock position)?

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How did you check the head gaskets?

 

When mine went, there was no mixing of coolant or oil in either systems. EJ HGs can weep lightly for a period of time before they let to and become an issue. I believe mine were doing this for some time before running the engine hot but not straight to the red unless I was in really slow traffic on a warming/hot day. I drove it for two days like this before the engine was stripped down.

 

If you suspect the HGs, just do them, especially if they've not been done before ;)

 

Cheers

 

Bennie

I just checked the oil and coolant, I changed both this week and drove around 1000km and after checking they both look clean, thats it. The temperature gauge never went above the optimal temperature value.

 

In case it my HG would be starting to get bad, it still would not explain why the thermostat does not open right? 

 

 

It has nothing to do with the ECU.

 

Clogged exhaust or catalytic converter?

 

When it’s overheating does the cabin heat blow cold?  Nope

 

What kind of daily temps are you seeing, what country and flat easy driving or mountainous dirt road climbs? New Zealand, so pretty hilly but temperate

 

I would get the temp gauge working properly. Replace sensor and swap in another instrument cluster (which is really easy just get a used one). Or pull and inspect yours to see if you can repair it. Or get an aftermarket gauge while you figure this out. Either way Get some real data. I replaced both sensors, and tested the old and the new, all 4 work fine. measures resistance and compared to constructor data.

 

Blown headgasket. If they’re not blown yet they’re going to driving while overheating. Every engine ever made blows headgaskets if it’s driven hot.

 

Oil and coolant DO NOT mix on that engine, or if they do then the condition is so bad you know what the issue is without needing to check. When it’s overheating it’ll push exhaust gases into the coolant and the pump cavitates.  

To verify find a shop with a $$$$$ has analyzer and they can detect gases i the coolant.  thanks, i did not know that ! will look for one. (does this explain the closed thermostat?)

 

 

Or Something is clogging the coolant flow. You seem confident this isn’t the issue. But I’d check the radiator. How do you know it’s flowing enough?  When driving without thermostat I can tell the radiator works fine, when I purged it with the garden hose the flow was very good.

 

Or I’d pull the water pump and inspect it. They dont really fail on that engine but at this point you need to verify it can properly move sufficient fluid. New Pump last year

 

Pretty simple - clogged, pump or headgaskets. That’s it. I didn't know that coolant and oil didnt mix in this engine, id be relieved if its a head gasket. I don't understand the link to the thermostat staying closed though.

 

It seems odd to me that the gauge goes to the right position like it working but you think it’s overheating. me too, its really weird, and that the fans dont turn on either... both sensors work fine this im sure of it,

 

 

I just have 2-3 oddball things to contribute

 

I think that car has 2 temp sensors, one for the gauge only, the other is for the ECU - did the correct one get changed? (it's possible it has newer style with both sensors in one unit) yup youre right ! I changed both :)

 

 

I wonder if the heater core is clogged? The circuit that flows through is needed so the t'stat works correctly. As a test, you can bypass the heater core and loop the 2 hoses together i tried to turn the heat on and off, and it works fine, so I assumed it was not clogged, but I could test with a bypass.    The bottom radiator hose stays cold but the water pump inlet where the thermostat sits, engine side, is really very hot.

 

 

is the 'jiggle pin' in the t'stat at the top (12 o'clock position)? Wow I had no idea there was a position for this. I probably didnt put it the right way, but I would think my mechanic friend did when he tried in his garage. When i removed it (for a 5th or 6th time) the coolant was flowing through the jiggle pin though.

 

 

thanks a lot for your inputs guys, I'm gonna look more into a head gasket. If anyone can explain the link between bad HG and a thermostat not opening despite high coolant temperature that would be great.

 

Thanks

Edited by quentindc

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If the gauge stays solid where it should be, and the heat blows hot air, and the radiator does not boil over, then I don't think it is overheating. Many times, an oil leak, especially when it gets on the exhaust, will give an impression of "hot" because of the smoke and smell. I would get an infrared tester or even a cooking thermometer stuck down in the radiator for a second opinion.

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How do you know that the thermostat isn't opening?

As stated, the heater circuit is what's used to open the thermostat/regulate engine temp. I've had my engine block frozen, including the radiator and heater core. Long story short, even with the heater circuit frozen the engine managed its temp just fine and managed to thaw out the radiator without damaging the block. HGs held on for another 3 or 4 years after this!

 

One way to gently test things is to go for a drive to warm the car up, then leave it idling in the driveway with the heater OFF. Monitor the temp gauge when doing this (it should take 5 - 10 mins depending on weather), Idle engine and allow it to trigger the thermo fans. IF the temp gauge climbs to 3/4 and there's no fan action you need to look into why. The fans should kick in without ANY change to the temp gauge on the dash. You need to allow time for ALL the coolant in the radiator to heat up for the thermo fans to be triggered. If the radiator is new it may give off a funky smell as it heats up, my all copper heater core did the same thing for ages.  And as mentioned, there could be an oil leak that's causing the smell that seems to have raised the alarm for you.

I also recommend getting a mechanical aftermarket temp gauge - and tap it into the heater hose - I believe it's the upper one that is the heater IN line. This is the one to tap into so that the use of the heater doesn't interfere with your readings. You will need to knock up a block to fit this. I used some plumbing items, threads were close and I've not had any problems with leaks for many years:

p8251806.jpg

 

Going by my mechanical temp gauge, thermo fans kick in at about 93*C, off at about 87*C, normal operating temp in cold weather is 82*C solid - it won't move!


Do you know if the ECU has ever been changed in this car, or whether there's been any wiring mods for whatever reason done under the dash? Long shot here - the wire to trigger the thermo fans from the ECU may be damaged and not allowing the signal to get through.  To test this wire you'll have to work out a way to test it's continuity with a multimeter.

 

Or get an infra red temp sensor to do some quick easy testing of temps.

 

Cheers

Bennie

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It’s been such a classic sign of EJ25Ds for 20+ years. I’ve never considered why the lower hose stays cool when the headgaskets fail. Generally the exhaust gases are screwing with coolant flow. I would guess the water pump can’t work right with all that air in there or the Tstat only works when submerged in fluid, not when surround by air.

 

I’m starting to also wonder if there even is any actual overheating. The temp gauge is acting normal, not like it’s broken. I’d start trying to get some temp readings of the engine and find out why your gauge isn’t working, who cares what you replaced if you still think it’s not working....if you really think it’s not. Then maybe you’ll also verify the engine is actually fine as well.

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If the gauge stays solid where it should be, and the heat blows hot air, and the radiator does not boil over, then I don't think it is overheating. Many times, an oil leak, especially when it gets on the exhaust, will give an impression of "hot" because of the smoke and smell. I would get an infrared tester or even a cooking thermometer stuck down in the radiator for a second opinion.

 

This!

 

As mentioned, this car has 2 temp sensors, one for the ECU (which controls the fans) and one for the gauge.

 

You've tested the fan circuitry, and all appears to be working. So I'm assuming that the ECU does not think the engine is hot (this could be verified with a scan tool).

 

Your gauge reads fine.

 

You've replaced one of the sensors, even if it's the wrong one, you've got 3 sensors telling you the engine is not overheating. Those sensors are mounted in the coolant bridge right over the cylinders, even with zero forced coolant circulation, thermosiphoning would bring the hottest coolant to them.

 

 

 

The only symptom of overheating is a smell. If you want to verify it, get your hands on an infrared thermometer. I bought one last fall on Amazon, it was pretty cheap ($10?), and has been really useful for a lot of things (I found a couple weak links in the insulation of our house this winter....probably paid for itself right there). Point it right at that coolant bridge, it shouldn't be much warmer than the opening temp of the thermostat.

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Quentin, while you are working on this issue - always check coolant level in the radiator itself, don't trust the 'level' in the overflow bottle to refelct actual cooling system volume.

 

also, has coolant ever been pushed out of the overflow?

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I think that Subaru Scott has or is close to the right answer.  First of all, when the cooling system is up to temp and everything is working, the lower hose should be cool.  That is the function of the radiator, to cool the coolant down before it is drawn back into the engine.  The upper radiator hose should be hot.

 

You may have a slight leak of either coolant or oil somewhere that is getting onto a hot exhaust component such as the manifold.  It can be a very slight leak.  If it is coolant, it could takes weeks or months before the coolant drops enough to notice.  A small oil leak could be so slight that it doesn't drop significantly between normal oil changes.

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i had a leak once in my radiator that went for years after i only saw it when i was in cold weather in massahusets and the engine was running when i was at a lit up gas station and i saw some steam. just saying

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If the gauge stays solid where it should be, and the heat blows hot air, and the radiator does not boil over, then I don't think it is overheating. Many times, an oil leak, especially when it gets on the exhaust, will give an impression of "hot" because of the smoke and smell. I would get an infrared tester or even a cooking thermometer stuck down in the radiator for a second opinion.   

 

I think it's overheating because when I let the car idling for 45 min or when I drive for like one hour, the lower hose is still cold ans fans still don't work. The upper hose it really burning hot and the engine block as well. My Mechanic friend tested it with his infrared thermometer and told me the heat should trigger the fans / open the thermostat (which was happening like 6 months ago after 15min of idling).

 

How do you know that the thermostat isn't opening? After driving for long periods of time the lower hose stays cold, and there is no pressure in the radiator.

 

As stated, the heater circuit is what's used to open the thermostat/regulate engine temp. I've had my engine block frozen, including the radiator and heater core. Long story short, even with the heater circuit frozen the engine managed its temp just fine and managed to thaw out the radiator without damaging the block. HGs held on for another 3 or 4 years after this!

 

One way to gently test things is to go for a drive to warm the car up, then leave it idling in the driveway with the heater OFF. Monitor the temp gauge when doing this (it should take 5 - 10 mins depending on weather), Idle engine and allow it to trigger the thermo fans. This does not happen any time now, however long I leave the car idling or drive around the fans don't turn on, the thermostat does not open.

 

IF the temp gauge climbs to 3/4 and there's no fan action you need to look into why. The gauge never goes above 1/2. The fans should kick in without ANY change to the temp gauge on the dash. You need to allow time for ALL the coolant in the radiator to heat up for the thermo fans to be triggered. If the radiator is new it may give off a funky smell as it heats up, my all copper heater core did the same thing for ages.  And as mentioned, there could be an oil leak that's causing the smell that seems to have raised the alarm for you.

 

I also recommend getting a mechanical aftermarket temp gauge - and tap it into the heater hose - I believe it's the upper one that is the heater IN line. This is the one to tap into so that the use of the heater doesn't interfere with your readings. You will need to knock up a block to fit this. I used some plumbing items, threads were close and I've not had any problems with leaks for many years:

 

 

Going by my mechanical temp gauge, thermo fans kick in at about 93*C, off at about 87*C, normal operating temp in cold weather is 82*C solid - it won't move!

 

Do you know if the ECU has ever been changed in this car, or whether there's been any wiring mods for whatever reason done under the dash? Long shot here - the wire to trigger the thermo fans from the ECU may be damaged and not allowing the signal to get through.  To test this wire you'll have to work out a way to test it's continuity with a multimeter.  Good idea, I need to look more into this as I actually have no idea where the ECU is and which wires control the fans.

 

Or get an infra red temp sensor to do some quick easy testing of temps.

 

Cheers

 

Bennie

 

 

It’s been such a classic sign of EJ25Ds for 20+ years. I’ve never considered why the lower hose stays cool when the headgaskets fail. Generally the exhaust gases are screwing with coolant flow. I would guess the water pump can’t work right with all that air in there or the Tstat only works when submerged in fluid, not when surround by air.  This actualy could be it ! Do you know of any other signs of HG fails ?

 

I’m starting to also wonder if there even is any actual overheating. The temp gauge is acting normal, not like it’s broken. I’d start trying to get some temp readings of the engine and find out why your gauge isn’t working, who cares what you replaced if you still think it’s not working....if you really think it’s not. Then maybe you’ll also verify the engine is actually fine as well.  I'll try to get a hand on an IR thermometer, it costs a lot here in NZ.

 

 

This!

 

As mentioned, this car has 2 temp sensors, one for the ECU (which controls the fans) and one for the gauge.

 

You've tested the fan circuitry, and all appears to be working. So I'm assuming that the ECU does not think the engine is hot (this could be verified with a scan tool).

 

Your gauge reads fine.

 

You've replaced one of the sensors, (I replaced both) even if it's the wrong one, you've got 3 sensors telling you the engine is not overheating. Those sensors are mounted in the coolant bridge right over the cylinders, even with zero forced coolant circulation, thermosiphoning would bring the hottest coolant to them.

 

 

 

The only symptom of overheating is a smell. If you want to verify it, get your hands on an infrared thermometer. I bought one last fall on Amazon, it was pretty cheap ($10?), and has been really useful for a lot of things (I found a couple weak links in the insulation of our house this winter....probably paid for itself right there). Point it right at that coolant bridge, it shouldn't be much warmer than the opening temp of the thermostat. Next investment, IR thermometer, I'll get some real data on this.

 

 

Quentin, while you are working on this issue - always check coolant level in the radiator itself, don't trust the 'level' in the overflow bottle to refelct actual cooling system volume.

 

also, has coolant ever been pushed out of the overflow?   No it's always been fine. With thermostat on, the coolant stays cold in the radiator, and with thermostat removed the coolant is flowing correctly and radiator level stays good.

 

Thanks for your inputs, I'm gonna look into all this.

 

 

I am still wondering, when I remove the thermostat and leave the car idling for like 45 min, the fans still don't turn on. The coolant flows fine and the engine heats at a temperature which should trigger the fan (it was the case 6 months ago). 

Also of exhaust gas come in the circuit, I should see bubbles coming out of the radiator when cap removed ?

Edited by quentindc

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Bubbles in the coolant means a weeping/blown head gasket if the cooling system was properly bleed to begin with.

 

I'll have a play with my ej22 and see if a disconnected temp sensor will trigger the Thermo fans. It's the brown plug on your driver's side of the coolant crossover pipe. A real PITA to get to.

 

We need those actual temp readings to properly know what's going on. What was the reading of the mechanic's IR thermometer?

 

Even at normal operating temp you shouldn't be able to touch the upper radiator pipe or any other part of the engine for that matter...

 

Cheers

 

Bennie

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Could be a blocked heater core that is preventing the thermostat from opening.  Try taking the hoses off the heater core and connecting them with a pipe fitting.  Then run the car.  The heater circuit feeds the back side of the thermostat letting it open.  No flow to back side and thermostat won't open.

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perhaps there is a wiring problem from the engine temp sensor? any sign of rodent damage or possibility of a pinched wire? Can you measure the correct value from the ECU?

 

the 4 things I guess I might try;

 

measure or inspect or find a way to bypass/parallel the eng. temp. sensor's wiring

 

get the nose of the car up, try to burp-out more air....get the rpms up to 3-4k a coupla times after the t'stat opens.

 

bypass the heater core with a piece of hard pipe

 

try another ECU

Edited by 1 Lucky Texan
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