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attention thermo dynamists

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18 replies to this topic

#1 Skip


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Posted 02 September 2003 - 05:42 PM

My AC is toast so off goes the heavy compressor, but the condenser coils in front of the rad are still intact.
We know they are good for high pressure and sit in the main air stream.
My thoughts and theory
I have been running no thermostat all summer in an attempt to see if this will cause overheating
(I have laboratory digital thermometers (J type thermocouples) in both the water jacket and the oil pan)
The results show a cooler by some 10 degrees average H20 temp and more importantly a 20 deg drop in oil temp
H20 before 195 - 205 Oil before 285 - 300
H20 after 185 - 195 Oil after 265 - 285
All degrees given in Fahrenheit
SO my question to our esteemed panel is
Do I plumb the AC condenser coils to run coolant, or do I plumb them with a thermostat to run oil?
(I planing on using an oil filter adapter commonly available with thermostat)
I am siding on running H20 as it seems to be the controlling entity in keeping the oil temps down.
They live in the same environment so it stands to reason they would share entropy.
The added volume of coolant or oil would not be enough to be a major factor in the Newtonian cooling equation.
The hot oil in the condenser coils infront of the rad may prove detrimental though.

Thanks for reading, any thoughts welcome.

#2 RedNed


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Posted 02 September 2003 - 06:33 PM

If all other componets of the cooling system are in good shape running without a thermostat will not cause overheating. Just putting in a cooler thermostat will help you run in the range you want.
As for moding the condensor to run oil or coolant I vote for oil. And move the condensor so it doesn't inhibit airflow to the rad.

My question would adding a second fan help keep temps down on the highway or is the air moving through as fast as it can anyway.
Maybe I want a oil cooler too except I'm worried about the winter.

My two bits...

#3 archemitis


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Posted 02 September 2003 - 06:42 PM

i like oil coolers. but if the oil is almost 100 degrees hotter than the radiator, and its in front of the rad, what if it heated things up?
electric fans on the highway dont do anything, cuz at speed it has pleanty of air.
what about runing an extra heater core infront of the rad? arent the passages through the ac condenser pretty small compared to the rad, and coolant lines.
thats interesting about the oil temp. i thought it would be alot less in a water cooled motor. the oil in my harley (air/oil cooled) stays around 200, thats in the tank though(wet sump system).
cant have too much cooling, or sensors!

#4 beauregaardhooligan


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Posted 02 September 2003 - 07:42 PM

I say water.
I also say a fan can help at hiway speeds, especially when there is an AC cooler also.
IM(not so)HO

#5 asavage


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Posted 03 September 2003 - 12:06 AM

Don't use the condenser for either. It's not designed to be compatible with green (silicate-based anti-corrosion) coolant, and the organic-acid-based orange/pink coolants aren't compatible with your brass radiator (if yours is brass, that is). It won't flow enough coolant to do much good anyway. It'll just end up being your coolant filter: in a parallel-flow plumb job, there won't be enough pressure to keep fines in suspension, and they'll settle in the condenser. In a series-flow plumb job, the condenser is too much of a restriction :(

You *might* use it for oil. It'll handle the pressure, there aren't any corrosion issues. It'll be hard to drain at oil change time, though. And, it *is* possible to over-cool oil, esp. organic oil. You really need it up over about 220° pretty quickly. Drives out water through the PCV system.

The reason you want to cool oil over cooling coolant is the larger delta T of oil to air: The oil is hotter than air by a greater amount than the coolant is hotter than the air. Greater difference in hot to cool temp = greater heat flow. Therefore, you can dump more heat out of the oil than you can out of the coolant, assuming the same surface area and media flow rates -- this last is theoretical, of course.

Also of course, this ignores the fact that once you dump the heat out of the oil, you've decreased the delta T of the coolant, because the condenser is dumping heat into the rad's airstream.

On the topic of removing the thermostat: fine for experiments, lousy for engine and oil life on gasoline-fueled engines. It takes much longer to come up to operating temp (undoubtedly you've noticed this), condensate water in the crankcase (byproduct of combustion, gets past rings, and a lot of it is produced when cyl walls are cold) mixes with acids formed during combustion and present in non-synthetic oils, combine to form sludge, which doesn't lubricate very well.

Keep those warmup times short and those temps up for long engine life. OEM = 195° for coolant, isn't it?

[I just replaced my themostat, because somebody had put a 180° one in, and the dash gauge barely moved. It was regulating to an actual 167°. I used an infrared "gun" to measure. Changed to an OEM 195° t-shat, measured at the thermostat housing 193°. Nice.]

(LPG fueled engines are a different story)

#6 GLCraig



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Posted 03 September 2003 - 01:34 AM

actually OEM=88degC ~ 190degF

I know BFD

#7 Skip


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Posted 03 September 2003 - 07:36 AM

Thanks for the relpies

Savage, very well said, but I have some issues with your reply, please this is a debate not an argument.

a) May cars have aluminum rads, are the condenser coils
a different alloy? The coolant manuf. says "Safe for Aluminum radiators"

B) Flow rates. I was planing on semi-parallel. I am going to plumb it in series with the heater core return hose, grant it the delta T will not be as high because of the heater core dropping some of the heat. BTW Our EA82 cores are not valved and the heater core does not exchange much heat when the blend door is bypassing the air flow.

in a parallel flow plumb job, there won't be enough pressure to keep fines in suspension, and they'll settle in the

I do not know what you mean by fines? Fine particulate matter?
You must be saying the heater core's cooling tubes diameters are large engough to not let this happen.

Oil's viscosity is higher than coolant even when warm, it's surface adhesion is close to coolant, yet it will flow where coolant will not?? You must be taking into account the oil system pressure.
The adapter mentioned, runs the oil in a parallel system once it's Tstat is open. Are you aware of this?
This is a very good point I will test this theory if you do not mind.

Yes I am aware of the oil needing to be in the 220 deg F range for reasons you state, thus the thermostat in the oil cooler line.
Hope everybody reads this.

As you can see from my empirical results the delta T between air and the oil is not that much larger than the coolant. Am I correct stating that the heat exchange rate is function of delta T linearly, not exponentially?

c) On the running with no thermostat, here is where it gets messy.
I should have stated this is for the summer month usage, sorry.
That said.

I am sorry to report, my findings disagree with your knowledge.
During the summer months where the ambient temperature is above 65 deg, it takes less than 3 minutes for the oil and coolant temp to get to the vaporization point of combustion by products and H20.
I used a stop watch to measure this. Before removing the Tstat the time was 2 min 15 sec. Sorry, maybe this being a turbo charged car (although the turbo is not making much pressure during my low speed warm up) has something to do with the quick warm up time. I must admit before I saw this I believed what you said. There are a lot of wive's tales floating about. That is why I ran the experiment.
Time to temp. was part of the experiment.
I am NOT condoning this as in the cooler months it would be as you describe. But we do not suffer cooling problems in those months.

d) On the Tstat temp, yes the OEM is 190 deg F, but at 180, the engine still gets to a vaporizing state, the ECU goes into closed loop at 140 deg and everything remains cooler, thus the tolerances are tighter and the oil stays above 220 but below 300 by a larger amount, sorry to have to disagree with you again.
I say again. This again is for warmer months
The delta T in the heater core causes poor heat transfer in the dead of winter at 180, a 190 must be used. I believe the actual temp of the
OEM is 193, the almost 15 deg makes quite a difference.
This again I have proved but not with empirical figures.
Speaking empirically
I have no empirical figures for the performance gain with a 180 vs 190, I have only read where gains are possible, but the margin of increase to a pressure threatening 230 coolant temp would have me using a 180 in the summer and a 190 in the winter.
Head cracks and gasket failures in our cars are real.
Keeping the coolant passage pressures down is a worthy goal.
In theory, the adiabatic nature of the infernal internal combustion engine must suffer when it's temp is higher, as the ol' delta T is higher and more energy is lost to the surrounding air, thus lowering it's efficiency - do you agree?
I for one must say I appreciate your knowledgeable reply and look forward to your rebut.

#8 Rallywagon


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Posted 03 September 2003 - 12:35 PM

I suggest using a simple oil to water cooler that mounts between your oil filter and block. IF you can shed the heat at the radiator, it provides a nice system that regulates oil temp using the cooling system thermostat. As the engine heats up, the hot water helps warm the oil quickly, then it helps keep the oil temp lower on longer drives. With an oil to air cooler, you have to have a fancy thermostat valve so that in the winter your oil does not get too cold. Here is some info about the setup I describe.....


I plan to install one on my wagon when schedule permits. I know that there are some third party suppliers of these oil to air coolers for the aircraft EA81 entusiasts. Interestingly, my wife's Mazda MPV has this exact setup.


#9 mcbrat


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Posted 03 September 2003 - 01:55 PM

on my 84 Turbo Brat, there are 2 oil coolers installed. haven't had a chance yet to see how they are plumbed, but this vehicle has stayed the coolest of any of mine this scorching summer....

#10 RickOregon


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Posted 03 September 2003 - 03:30 PM

Hello Skip,

I tend to agree with asavage. If it were my rig, I wouldn't do either. I'd be more inclined to yank the condenser, thus improving air flow to the radiator, if you don't want a/c anymore, that is.. The condenser is specifically designed to optimize heat transfer in order to condense freon gas to freon liquid, isn't it? If you feel the need to provide more oil cooling, I'd go with Rallywagon's suggestion, as oil coolers, again, are specifically designed for optimal heat transfer from an oil circuit to a water circuit. (Some VW engines, notably the Cabriolet, have oil coolers that interface with the coolant system and are thermostatically controlled. IMHO, though, it's just one more system to fail...) That's just my 2 cents worth. What a laboratory you have there! 8-) Rick

#11 Skip


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Posted 04 September 2003 - 07:57 AM

great idea on the coolant to oil cooler, one thermostat controls all!!

Again might be the hot oil from the quickly warming turbo bearings but I was amazed at how fast the oil came up to temp.
Much faster than the coolant even with a coolant tstat in place.
With this type heat exchanger it's a definite win win.

I just wish I could trust that the automatic tranny cooler section of my rad (not used as it's a 5 speed)
would handle the 60 +psi oil pressure??
whoop!! there it is, a built in coolant to oil cooler!!!
I could make a low pressure aux pump driven loop from the oil pan and back I guess???

After a pressure drop test suggested by Al, I'm going to plumb the condenser coils into my heater core return line, (they practically cross paths) the extra coolant in the system may or may not help and if it will not flow only my frozen piggies will be the harm.
Ya know though
"Some men gotta hunt"
"Some men gotta fish"
--- well I gotta putz

Thanks again for the replies



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Posted 04 September 2003 - 09:33 AM

I thought the trans cooler might be a option...

With my turbo cars it seams like the turbo side of the engine runs hotter than the drivers side, I haven't tested this but it seems so. I considered using a oil cooler between the turbo and the engine to cool the hotter oil coming from the turbo, thought about doing the same with the water coming from the turbo. Volvo's have a nice oil cooler, might work.

If your cooling system is working properly, would you need additional cooling? If you goal is to change the temp of the water or oil to test performance, you try both and see what happens. If your goal is to reduce the engine temps, then whether the heat is extracted from the oil or water wouldn't make that much diff would it?

#13 Skip


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Posted 04 September 2003 - 09:54 AM

Let me start with
"I considered using a oil cooler between the turbo and the engine to cool the hotter oil coming from the turbo "
The oil being discharged by the turbo is a gravity feed "drop or drip" into the oil pan, some form of aux hitemp pump would be needed.
In this case cavitation of the pump is a possibility, but the pump could be a centripetal low pressure pump - perfect for the likes of the trans cooler in the rad.

"thought about doing the same with the water coming from the turbo."
Here the coolant can be superheated and caution must be exercised in it's transport anywhere. (thus the special factory hose or the wide spread use of silicone replacements)

"If your cooling system is working properly, would you need additional cooling? " What is working fine today may not be this way forever.

"If your goal is to change the temp of the water or oil to test performance"
As stated previously these adiabatic system will increase in efficiency (and possibly perf.) any time the temp is lowered as long as the ECU still goes into closed loop and condensates are driven off by the heat of vaporization.

"If your goal is to reduce the engine temps, then whether the heat is extracted from the oil or water wouldn't make that much diff would it?"
A good point, I say more cooling for both given the limits prescribed in the above statement.

thinking is good

#14 ShawnW


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Posted 04 September 2003 - 10:25 AM

Id leave the condenser in. In my experience the condenser protects the radiator in that the radiator doesnt get a zillion dead bugs trapped in it.
That or id get a big oil cooler off some other car with the same oil filter thread as a Subaru, which happens to be a pretty common filter size from my experience. I think one from a Honda would work if they have an oil cooler on any of their Acura or high end cars.

#15 All_talk


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Posted 04 September 2003 - 11:45 AM

Hey Guys

Though thermo is not my specialty, I am a mechanical engineer and I’ll chime in here. I also have spent years working with air cooled VWs where oil is a far more critical part of the cooling system. Others have touched on a lot of important aspects but I will add a few thoughts.

The condenser coil would be a bad idea in series with the radiator, as this would obviously severely restrict coolant flow. In parallel it should add some cooling capacity, but I think it would be minor, specially when you consider the decrease in delta T it creates for the primary core, its effect might possibly be similar to turning on the heater and the increased air flow from removing it might have just as much affect (as RedNed stated). As for placing it in series with the heater circuit, most cars (I haven’t checked the subie yet), have a flow valve that shuts off or restricts the coolant flow when the heater is turned off, so unless you turn the heater on the condenser coil will not see any flow.

It should be a functional cooler for oil, though its placement is certainly less than ideal. But unless used with a thermostat that positively diverts flow through it (as opposed to just opening up a parallel path), it will most likely see little flow. And if used with flow diverting thermostat it may create a significant pressure drop in the supply to the engine, at the very least the pressure after the cooler should be checked (the stock sender is in the main gallery off the pump).

As for removing the coolant thermostat, the only thing to be gained by removing it from a properly functioning system is a slight increase in flow rate, if this shows a significant change in temp under normal running conditions there are most likely other issues that need to be addressed. And the disadvantages of running without a thermostat are real, yes in a specific situation a thermostat may not be necessary, but in general thermostats are a very good thing.

On the trans cooler, I’m not sure what the working pressure is, but some testing on a auto car with an inline pressure gauge should show if its in the right range.

XSNRG, any restriction in the low pressure drain side of the turbo’s oil system is a VERY BAD idea, it will inhibit oil flow through the turbo and most likely overheat the turbo shaft bearings. (edit-Skip covered this)


#16 MorganM


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Posted 04 September 2003 - 01:43 PM

Before modifying an AC condensor into another 'radiator' I would invest in a 2 or 3 core radiator. Why use a condensor and single row radiator to achieve what a 2 or 3 row radiaotr is designed to do? A nice 2 row and an oil cooler would keep you plenty cool. I picked up an OEM oil cooler for an EA82 from a guy in Europe where they came standard. Shouldnt be TOO hard to get your hands on one or an aftermarket one.

Just my 2 cents :)

#17 baccaruda



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Posted 04 September 2003 - 08:28 PM

how about putting an oil cooler in right before the turbo, in the higher pressure side?

#18 archemitis


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Posted 05 September 2003 - 10:40 AM

how bout pulling that ac condenser off to check how much air flow that restricts? coolant tems should drop a tiny bit.

#19 electryc_monk


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Posted 12 September 2003 - 08:20 PM

Ahhh Skipper this is a very stimulating thread, and I like where it has been going.

Here are a few of my thoughts and also a question or two with in it all....

First off before i forget :-p There is this idea of an external oilcooler and its location that has been bugging me on and off for over a year now. Like the Mitzu Eclpise Intercooler location mainly.

I have a line on a friends radiator shop that called a manufaturer of raditors for the idea of a 3 row or atleast a wide 2 row for the turbo wagon. Well after a couple weeks of then having the exact measurements i gave them the cost came back at (if memory is still correct) approx. $500 for two custom radiators as i was asking for two to replace the stock 2-cores in my (now two) then mine(silver) and 'Trina's (blue) wagons. And they would fit in the stock setup of the wagons' grill and would also handle the factory clutched fan or the narrow electric push pull designs...

anyways, the oil cooler location that i was planning on is still being mentally debated for that thermal disapation aspect. As i drive most of the year in Tejas and then visit the Michigan wonderland in the winter and occasionally in the summer the heat isn't really an issue to me but, the ice and slushy coldness on an oil cooler is a worry for condensation.

Then I was thinking of what Uncle Dave did with is ole Power Wagon back when I was in high school. Mounted the oil cooler on the fender well under the hood and then he set an electric fan over it to suck air across it and had the hood louvers only a few times directly over the cooler. Now the distance from the louvers to the cooler fins in not exact but I'd educated-guess it to be about 3-5 inches. Now I am going to relocate the air cleaner to inside the fenderwell with tubing for a "cold air intake" this would leave plenty of room for this small oil cooler to sit and then take one of those "deco-esque Outback hood vents" that i have and mount it to the hood above the oil cooler. Now the cooler would basicly be directly below this plate it also would be near and sorta under the cold air intake which would recieve some of the warmer air off the cooler but it would also protect the cooler from excess cold airflow. Maybe even mount a small( say 6" ) motorcycle cooling fan to the vent grate on the hood and that might do the trick?

The removal of the condenser should definately show a temperature change on the actual radiator reading. I'd bet more the 3 degrees F. Conservative bet. Yes it has been some time since I've had those automotive courses. And yes i am still working on those upper level physics classes but there is still alot to be said for the 'in training unoffical professional' (soft grin) - true?

Now about that reference to the oil to water cooler.
Working on the same principle as the water to air Intercooler there are more "parts to break" but if done in conjunction with the OEM coolant system then it would actually stay more balenced then with a seperate (read) stand alone oil cooling system - wouldn't it? (Whether its air to oil or seperate water to oil.)

Now for the Thermostat seesaw.

With such a significantly smaller window of thermal varience then *other* engines (VW bug's and busses not withstanding) the 195 vs. 180 vs. etal Tstats I have to say that the drive to Nevada and back with a 180 driving at freeway speeds and above with the A/C on the digi-dash thermo was never allowed to get in the red. *** grounding issue next*** the temp. stayed right about in the middle or one bar below the mid-point. Having said that it was in a fresh 50/50 or higher consentration of ethoyleneGlycol, one year old 2 core from Radiators dot com, and the 180 stat.

the previous summers roadtrip to michigan with a trailer had the (then) fresh outta the box radiator and a 195 Tstat and exactly 50/50 and it would run 2 or 3 bars from the redline..... and that was with occasionally using the A/C and not realizing the *grounding issue* back then.

(Calabz really brought this to my attention sooo...)
Beofre his cross-the Con-US trip he has the engine grounded and then even more grounded with heavier wire gauge and has since not seen near the "digital jump" that the "rest of us Digi-dashs" see with the water temp. so I am wondering how much the digi jump is when mapped against the mechanical or "other" electronic gauges your using in this experiment or other experiments? Even with the digi-jump that i omitted from the previous paragraph the temp readings still never actually hot the red bars.

Back to the oil coolers proximity to the oil filter concern.
The longer the hose/pipe is from the pump the smaller the reaction time for oil loss or leakage and faster the opportunity of turbo damage or actual engine damage due to oil pressure and flow drop offs.

Isn't that a legit worry when having any oil cooler in a system?

And isn't it logical to think/presume(sp) that the concern towards the critical window of the engines safe opporation is exponetial with the distance from the pump due to cavitation and /or loss of pressure due to lack of oil in the hydralic sytem?

I'll stop here and also ask Skipper if my ADHD/dyslexia needs a 'rewording' or whatever to unconfuse anyone.....

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