stock themostat vs. lower temp...

[slo5oh]

Has anyone played with running a lower temp t-stat? I'd like to see my normal operating temp lower then it is.

 

p.s. what is the stock t-stat temp?

[blitz]

I'm running a cooler stat. The stock one says: 78* C (172* F), the replacement says: 71* C (160* F). I believe these are cracking temps not fully-open temps.

 

The reason I went to a cooler stat was to reduce spark knock and to provide a hedge against head gaskets.

 

I've seen numerous cautions not to use anything but a genuine Fuji stat on a Subaru, so I was careful to get the Zero/Sports which is a Fuji. I'll post a link.

[blitz]

Vivid Racing is where I got mine, but I've seen it elsewhere. It's pricey.

 

http://vividracing.securesites.net/catalog/product_info.php?cPath=1_5_9_98&products_id=203&osCsid=b6442b8f55cb0f44a4f3ab2279dd9269

 

It says "for WRX", but I'm using it in my '02 2.5.

[slo5oh]

Why wouldn't I want to use a $3 special from a local autoparts store? If they work in every other car....

[Commuter]

Some have had troubles with aftermarket t-stats. I don't think the post is still on this board (it was ezboard), but one guy kept trying to track down a problem... finally resolved it by putting in an OEM t-stat. Another post... a heated pot of water test was done. The aftermarket t-stat acted quite differently from the OEM unit in it's "opening curve".

 

I know with my EJ25 Phase I engine, the "guts" of the t-stat are offset. That is, it has to go in in a certain position. (There is a notch for alignment.) Some aftermarket t-stats end up hitting the casting in the passageway and not opening fully. Just one of the Subaru quirks. I would still to OEM on this one.

 

Commuter

[Will Smith]

it should also be mentoned that your thermo switches may not open with a lower temp thmostat i tied a lower temp one and my gas mileage went down, returned to the stock temp and better running and economy was the result.

[TheMeatWagon]

http://www.ultimatesubaru.org/forum/showthread.php?t=16277&highlight=aftermarket+thermostat

 

Read that by general disorder... he changed me from gettin like a 180 degree aftermarket.

[Legacy777]

running cooler thermostats really don't do you any difference.

 

Look at what a thermostat does. It restricts flow to the radiator to help the car warm up faster. After temp has reached what it should, the thermostat opens....and pretty much stays open for normal operating of the engine. I don't think temps would get "too" cold for it to close back up partially.

 

So let's look at what happens when you run a colder thermostat. It opens sooner.....engine doesn't reach NOT as soon. mileage and efficiency will drop.

 

If you have a thermostat that doesn't open as much....I would think that would cause temps to elevate above what they normally are.

 

Bottom line, the ECU wants the temp of the engine to be in the 180-200 range. fans kick in at 200, or very close to it. You need to modify the ECU or the coolant temp sensor if you really want the car to run "cooler" But if you run cooler, you're not going to be running as efficiently.

 

The colder spark plug thing is the same way. A buddy with a 2.5 RS put a colder plug in thinking it would help since he had some "mods" the mods were simple bolt on......his car ran like poop and gas mileage sucked. We put the right plugs in....car ran much better.

[blitz]

The analog voltage from the temp sensor tells the ECU when to change from open loop to closed loop operation. I don't know exactly what the threshold figure is, but I'd always heard it was right around 160* F. The genuine Fujji stat I installed lists it's opening temp as 160* F which would explain why I'm not experiencing any adverse effects on fuel mileage (It's not forcing my motor to stay in closed-loop any longer than the stock stat does).

 

I spend virtually no time idling or sitting in traffic jams, and have adequate airflow through my radiator. True, that when the vehicle is not in motion, the coolant temp will climb towards the "on" temp of the fans, except that now I have a 12 degree head start, which means that my fans aren't forced to come on very often. This saves the fans and it saves the energy to power the fans. My combustion chambers operate a little cooler, the intake ports are a little cooler, and the power-robbing heat-soaked aluminum intake manifold runs a little cooler. I have a cooler air-charge entering my cylinders. Net result: 2 free Ft. Lbs. of torque and one point lower octane requirement (which I take advantage of by advancing the timing a little to obtain even more torque).

 

So here in the middle of failure stories, you have a success story. When it's time to replace this stat, I'll probably use the same part again (if it's still available).

[Legacy777]

The analog voltage from the temp sensor tells the ECU when to change from open loop to closed loop operation. I don't know exactly what the threshold figure is, but I'd always heard it was right around 160* F. The genuine Fujji stat I installed lists it's opening temp as 160* F which would explain why I'm not experiencing any adverse effects on fuel mileage (It's not forcing my motor to stay in closed-loop any longer than the stock stat does).

I don't get what you're trying to say with your last statement in quotes...you talk about going from open to closed loop earlier, which the temp sensor is a contributing factor in the ECU's decision to go from open loop to closed loop and back, along with a few other sensor inputs, like the O2 sensor and so forth. However upon startup/warmup I would venture to say that the ECU is open loop. Would you agree?

 

I spend virtually no time idling or sitting in traffic jams, and have adequate airflow through my radiator. True, that when the vehicle is not in motion, the coolant temp will climb towards the "on" temp of the fans, except that now I have a 12 degree head start, which means that my fans aren't forced to come on very often. This saves the fans and it saves the energy to power the fans. My combustion chambers operate a little cooler, the intake ports are a little cooler, and the power-robbing heat-soaked aluminum intake manifold runs a little cooler. I have a cooler air-charge entering my cylinders. Net result: 2 free Ft. Lbs. of torque and one point lower octane requirement (which I take advantage of by advancing the timing a little to obtain even more torque).

I don't think that 12 degree of head start is going to last you your entire drive to really make a difference. I could be wrong, but I sort of doubt it.

 

As for your other claims of stuff running cooler and more power, do you have any proof/data to back those claims up, or are they more or less like the "butt dyno?

[blitz]

I don't get what you're trying to say with your last statement in quotes...you talk about going from open to closed loop earlier, which the temp sensor is a contributing factor in the ECU's decision to go from open loop to closed loop and back, along with a few other sensor inputs, like the O2 sensor and so forth. However upon startup/warmup I would venture to say that the ECU is open loop. Would you agree?

 

Exactly. The stat I've installed doesn't contribute to holding the vehicle in the fuel-wasting, open-loop mode any longer than the stock stat does. Reason: the stat I've installed remains fully closed until the transition to closed-loop's been made. I make no mention of "earlier" anywhere, somehow you managed to interject that.

 

If a person were to install a stat that opened at a temperature below the ECU's switchover to closed-loop mode, it would have the effect of holding the vehicle in open-loop longer or possibly indefinitely (depending on ambient temps and how cold the stat is). That's not a good thing.

 

I don't think that 12 degree of head start is going to last you your entire drive to really make a difference. I could be wrong, but I sort of doubt it.

 

When I come to a stoplight and there's no airflow, the coolant temp rises to the fan's on-temp. When the vehicle is back in motion, the coolant temp drops back to the point dictated by the stat, PROVIDED: that the cooling system's capacity has not been exceeded.

 

As for your other claims of stuff running cooler and more power, do you have any proof/data to back those claims up, or are they more or less like the "butt dyno?

 

Matt, c'mon now. The torque loss to heat buildup in the aluminum intake is painfully obvious. It's an accepted fact that a 10* F reduction in air temp is equivalent to a 1% increase in air density. I'm not discovering magical gains with what I'm doing here, I'm just struggling to prevent losses, in small increments. You yourself have done the TB bypass in seach of a 3 degree reduction in intake air temp. Why? Me thinks you just trying to pick a fight at this point, but if you're engaging in playful banter, OK I'll play along.

 

Mmm..., I just went back and re-read my earlier post (the one in question here), and I had the term "open-loop" & "closed-loop" erroneously switched at one point. Apoologies if that causedconffusion.

[Ranger83]

How did you document these gains, then? Or you're basing it on your calculation?

[Legacy777]

Exactly. The stat I've installed doesn't contribute to holding the vehicle in the fuel-wasting, open-loop mode any longer than the stock stat does. Reason: the stat I've installed remains fully closed until the transition to closed-loop's been made. I make no mention of "earlier" anywhere, somehow you managed to interject that.

I think your switching of open loop and closed loop in your previous post is what had me confused

 

 

When I come to a stoplight and there's no airflow, the coolant temp rises to the fan's on-temp. When the vehicle is back in motion, the coolant temp drops back to the point dictated by the stat, PROVIDED: that the cooling system's capacity has not been exceeded.

Again, I'm going to ask, where did you get your data, how do you know it drops back to the point dictatec by the stat? Have you taken readings from the ECU?

 

I'm not trying to argue here, just to discuss. I have watched the temps for my car on the select monitor and seen what the normal operating temp range is. Bottom line is the ECU controls what temp range the engine is going to run at, NOT the tstat. All the data and info I've read/learned supports my opinion that putting a lower temp tstat in a stock car without modifying the ECU is a waste of time and won't change things.

 

The reason I'm asking for data or proof is not to argue, but to learn if my opinion is incorrect, and can be proven incorrect by data/facts.

 

Matt, c'mon now. The torque loss to heat buildup in the aluminum intake is painfully obvious. It's an accepted fact that a 10* F reduction in air temp is equivalent to a 1% increase in air density. I'm not discovering magical gains with what I'm doing here, I'm just struggling to prevent losses, in small increments. You yourself have done the TB bypass in seach of a 3 degree reduction in intake air temp. Why? Me thinks you just trying to pick a fight at this point, but if you're engaging in playful banter, OK I'll play along.

 

Mmm..., I just went back and re-read my earlier post (the one in question here), and I had the term "open-loop" & "closed-loop" erroneously switched at one point. Apoologies if that causedconffusion.

I think you mean Josh....not Matt.

 

As for the "accepted" fact.....I don't think so. That may be a good rule of thumb, but in any good experimentation or engineering testing, you support/dispute a rule of thumb or practice by testing and real data. If you could show me a 10 degree drop in air temp via sensors across a range of engine operating conditions, then yeah I'll believe that rule of thumb.

 

Yes I have done the TB bypass mod to reduce heat soak in the TB and intake. Has it helped, yes. By how much, I don't know, and I'm not going to begin to try and quantify how much gains/improvement/etc were had by doing this. Without doing a lot more testing, I can't give that info. Qualitatively I can say that throttle response is better, the car feels a little more peppy, and the TB is a little cooler.

 

Again....I'm not trying to pick a fight, just have a discussion. If you can provide data/facts to support what you're saying, I have no problem saying I am wrong, but until then, I'm going to go on my opinion based off the facts and knowledge I have learned.

[blitz]

How did you document these gains, then? Or you're basing it on your calculation?

 

I used the calculation and driving impressions. Before you begin howling, allow me to explain. I make a living on my ability to make subjective judgements (audio) and I've gotten good at getting past the mental gymnastics that go along with it.

 

A couple summers back I fabricated a set of 1/2" thick intake manifold thermal spacers in an attempt to reduce the intake manifold heat-soak power losses. It was painstaking work to trace out and router the parts by hand (I used a really hard & dense paper-based phenolic). I secured the necessary extra manifold gaskets and longer intake manifold bolts, and after installing the spacers and driving around for a day, I pulled 'em back out. Why? Simply, they made my car slower. Granted, it was only a little tiny bit slower, and given the amount of time and work that went into the project it would've been tempting to convince myself that the car was actually a little faster, but I don't play that game. The mistake was that I used the gaskets (rather than the ports themselves) as a template to cut the spacers, causing turbulance in the ports.

 

I've said it before, I got suckered into buying an e-ram electric supercharger. After installing the unit, I routed the activation switch temporarily into the cockpit so I could control activation manually, then took a drive, came back and pulled the e-ram out. No bones about it, it made the car slower. It might've been only a 2 ft. lb. loss in torque, but I could feel it. I wanted very badly to feel more power with the e-ram installed but it wasn't there.

 

Bottom line is that I'm just being honest about what's worked for me and what hasn't. I've got no reason to BS.

[friendly_jacek]

Interesting discussion here.

If I were to take sides in this argument:

 

"When I come to a stoplight and there's no airflow, the coolant temp rises to the fan's on-temp. When the vehicle is back in motion, the coolant temp drops back to the point dictated by the stat, PROVIDED: that the cooling system's capacity has not been exceeded."

 

vs.

 

"I have watched the temps for my car on the select monitor and seen what the normal operating temp range is. Bottom line is the ECU controls what temp range the engine is going to run at, NOT the tstat."

 

I would choose the first explanation. I observed the temp via OBD2 reader too and I am not convinced that ECU controls engine temp.

For example, during high speed hwy driving in mildly hot day with moderate load, the engine temp received by ECU is constant at 180F. At idle, it fluctuates between 180-212F.

How could possibly ECU regulate the Hwy temp?

Heck, I will buy the lower stat and do before and after measuments.

[blitz]

I think your switching of open loop and closed loop in your previous post is what had me confused

 

 

 

Again, I'm going to ask, where did you get your data, how do you know it drops back to the point dictatec by the stat? Have you taken readings from the ECU?

 

I'm not trying to argue here, just to discuss. I have watched the temps for my car on the select monitor and seen what the normal operating temp range is. Bottom line is the ECU controls what temp range the engine is going to run at, NOT the tstat. All the data and info I've read/learned supports my opinion that putting a lower temp tstat in a stock car without modifying the ECU is a waste of time and won't change things.

 

The reason I'm asking for data or proof is not to argue, but to learn if my opinion is incorrect, and can be proven incorrect by data/facts.

 

 

I think you mean Josh....not Matt.

 

As for the "accepted" fact.....I don't think so. That may be a good rule of thumb, but in any good experimentation or engineering testing, you support/dispute a rule of thumb or practice by testing and real data. If you could show me a 10 degree drop in air temp via sensors across a range of engine operating conditions, then yeah I'll believe that rule of thumb.

 

Yes I have done the TB bypass mod to reduce heat soak in the TB and intake. Has it helped, yes. By how much, I don't know, and I'm not going to begin to try and quantify how much gains/improvement/etc were had by doing this. Without doing a lot more testing, I can't give that info. Qualitatively I can say that throttle response is better, the car feels a little more peppy, and the TB is a little cooler.

 

Again....I'm not trying to pick a fight, just have a discussion. If you can provide data/facts to support what you're saying, I have no problem saying I am wrong, but until then, I'm going to go on my opinion based off the facts and knowledge I have learned.

 

We've both removed the coolant hoses from the throttle bodies on our engines because we both know that adding heat (by any means) to the intake airstream costs power.

 

I've discovered a paint-on, chemical-resistant, thermal-barrier which I intend to apply to the inside of my manifold and intake ports to keep the intake air cool (as soon as I locate a spare manifold). After I do that, I may swap back to the 192* thermostat. But until then, the 180* is the best I can do to reduce intake manifold and port temperatures.

[blitz]

Here's a quote from Jim Bell (founder of Kenne-Bell Superchargers).

 

"• 130 degree hotter air charge from exposed underhood filters can result in 14% (1% for every 10 degrees) decrease in horsepower."

[Legacy777]

Interesting discussion here.

If I were to take sides in this argument:

 

"When I come to a stoplight and there's no airflow, the coolant temp rises to the fan's on-temp. When the vehicle is back in motion, the coolant temp drops back to the point dictated by the stat, PROVIDED: that the cooling system's capacity has not been exceeded."

 

vs.

 

"I have watched the temps for my car on the select monitor and seen what the normal operating temp range is. Bottom line is the ECU controls what temp range the engine is going to run at, NOT the tstat."

 

I would choose the first explanation. I observed the temp via OBD2 reader too and I am not convinced that ECU controls engine temp.

For example, during high speed hwy driving in mildly hot day with moderate load, the engine temp received by ECU is constant at 180F. At idle, it fluctuates between 180-212F.

How could possibly ECU regulate the Hwy temp?

Heck, I will buy the lower stat and do before and after measuments.

Yes you are correct. If you are traveling on the hwy with adequate airflow to the radiator, there's no need for fans....ie ECU to regulate temp.....and yes in that case, I agree that the tstat is more or less regulating the temp. If the radiator cools the coolant too much, the tstat will close slightly and start to restrict flow, which "should" bring temps back into where they're suppsed to be. I will say however that the OEM tstats have a higher resistance to temperature changes. So they're not going to open and close much if at all due to temperature swings. I found this out when I put an aftermarket tstat in, and experienced weird issues with the temps decreasing.

 

I do think that what I orig. said is not necessarily totally true, because in certain circumstances the tstat is doing more of the regulating of the temps.

 

So I guess depending on what type of driving you do most will inherantly determine what temp control device (tstat vs ECU/fans) is regulating the engine temp.

[Legacy777]

here's a pretty good thread over on nabisco

http://forums.nasioc.com/forums/showthread.php?p=7244879

 

I still do agree with them and what I said earlier that it's really not necessary on a stock engine, and it will hurt emissions and such.

[blitz]

Josh, agreed. The hotter stat temps are tied to emmissions regs, primarily hydrocarbons.

 

IMHO, the problem with NABISCO is the poor S/N ratio. There's a few really knowlegable people that get drown out by a plethora of yuks that hash & re-hash false internet-tech.

[Legacy777]

yeah....you have to wade through a lot of info and take it with a grain of salt until you verify it yourself, or know the person posting it knows what they're talking about.

[slo5oh]

Damn...

Didn't want to start a fight.

 

The last couple posts peg internet information as a whole. Be careful what and who you take advice from. My experience is with high HP 5.0 ho engines, supercharged and N/A. I've seen sooo many people put a 160 (stock is 195) t-stat in and have all sorts of overheating issues in the summer months. Usually the 160 is not blamed since it was put in months earlier. What it comes down to is that, fans or no fans, the cooling fluids don't spend enough time in the radiator to cool off sufficently... so unless you were doing 50mph on the freeway you would always overheat.

Honestly in my soob I'm not looking to make 10 more HP or 10 more TQ... although another 10mpg would make me nut. With a simple basic understanding of engines, electronics, and mechanical parts I know that heat is your enemy. Cooler engines last longer, cooler air is more dense, cooler electronics burn out slower (they all eventually burn out). I know the engine needs to reach a certain temp to run at it's peak. I opted for a set of cast iron heads on one engine in place of the normal alum heads to keep temps in the combustion chamber up... (where the juice likes it)

 

In defense of Blitz:

I read Everything you posted and with my 10 years of tweaking assorted 200 to 600hp engines I'd agree with all of it. The phynolic spacer story amused me, hell it reminded me of a friend that ported his own intake and hogged the thing out sooo bad he probably lost 40lb of TQ, and no way did he gain any HP. There's a little thing called "intake port velocity" that he mangled. But his pride would not let him remove it and start over. It takes balls to admit you spent time and money on something and it failed. I still have some 3" black PVC I bought 2 years ago and was planning on using to bypass the stock breadbox intake... never got around to it though.

 

I'm no pro engine builder... just a garage fiend with friends-a-pleanty. Some of them are smart as hell, some are... well... not. But I learn from them all. Blitz seems to know what he's talking about. Since it looks easy enough to get at the t-stat I will try swapping to a 160 whenever I get around to draining the cooling system.