The Truth About Running Colder Thermostats

[Vettezuki]

So what's the deal. As usual, there seems to be two schools of thought.

1 - Especially for "high" performance engines, that is higher compression or forced induction, lower temp thermostats are "good" and "helpful". Run a colder thermostat than stock

2- That's horse shit. Engines are designed to run optimally in an operating temp range, arbitrarily forcing the temp down is not useful. Run a stock thermostat regardless.


FTR, I have a moderately high compression engine, somewhere north of 11:1. I'm currently running a stock stat, which I think is 190. Would I get any benefit in any context from running a colder stat?

[Damian]

I have 160 degree thermostat in the Goat and I think it runs much smoother than before.

[BRUTAL64]

Cooler is better. Just make sure the computer is set to use the cooler temp. If you don't it'll look for the 190 temp and not find it.

Cold air and fuel make more power.

Ok, before someone else states it---engines make more power at 200 to 220 degrees. But, that is a racing engine. What you need is to have enough temp to get the oil up to about 180 to 200 degrees so that all the water vapor is steamed out.:boggled:

[BRIAN]

Cooler is better. Just make sure the computer is set to use the cooler temp. If you don't it'll look for the 190 temp and not find it.

Cold air and fuel make more power.

Ok, before someone else states it---engines make more power at 200 to 220 degrees. But, that is a racing engine. What you need is to have enough temp to get the oil up to about 180 to 200 degrees so that all the water vapor is steamed out.:boggled:
nuff said:hail:

If your wondering, the car will run richer at a cooler temp than what the ECM is tuned for thinking the car hasn't reached operating temp.

[enkeivette]

Cooler is better. Just make sure the computer is set to use the cooler temp. If you don't it'll look for the 190 temp and not find it.

Cold air and fuel make more power.

Ok, before someone else states it---engines make more power at 200 to 220 degrees. But, that is a racing engine. What you need is to have enough temp to get the oil up to about 180 to 200 degrees so that all the water vapor is steamed out.:boggled:

Isn't the oil typically 20 behind the coolant? So wouldn't you want a minimum of a 200 degree tstat?

[BADDASSC6]

Brutal got it right for the most part. Decreasing the charge air temperature increase the air density therefore more O2 make it into the motor.

I like running lower temps simply because it helps with longevity of the motor.

Race engines do like to run hotter, but many times thats a materials issue. The comp cams spring that many lsx guys run are significantly stiffer than stock. The result is that they can become brittle when cool. As a data point my car runs 205-210 on the track and oil temps get ~255-270.

As far as the car running rich when cool, I don't really see that as an issue since most modern cars have charge air temperature as one of the variables they monitor.

[Vettezuki]

Brutal got it right for the most part. Decreasing the charge air temperature increase the air density therefore more O2 make it into the motor.

I like running lower temps simply because it helps with longevity of the motor.

Race engines do like to run hotter, but many times thats a materials issue. The comp cams spring that many lsx guys run are significantly stiffer than stock. The result is that they can become brittle when cool. As a data point my car runs 205-210 on the track and oil temps get ~255-270.

As far as the car running rich when cool, I don't really see that as an issue since most modern cars have charge air temperature as one of the variables they monitor.


Do you run a MAF tune or Speed Density? I was considering switching over to Speed Density. . .

[BADDASSC6]

Do you run a MAF tune or Speed Density? I was considering switching over to Speed Density. . .

Nope, MAF and I would recommend staying with it. Who did the tune on your car?

[Vettezuki]

Nope, MAF and I would recommend staying with it. Who did the tune on your car?

Z-Industries
http://www.z-industries.com/

The tune I'm running was done on and ostensibly for 91 Octane (it included mods to the computer not to through codes for my swap which doesn't have things the F-Body does.)

It will run in the winter on winter blend 91 acceptably well, but not in summer, it'll ping. It's also EXTREMELY mild tune, something like 18 degrees total. The motor supposedly was "only" 11.1:1 or so, but it must be higher than that not to be tunable for 91. The previous owner ran an agressive tune on 50/50 race/stree gas. He had headers and an LS1 intake and I have stock manifolds and an LS6 intake. He made about 430WHP in his C5 and I make about 390 in my C3.

[Damian]

Z-Industries
http://www.z-industries.com/

The tune I'm running was done on and ostensibly for 91 Octane (it included mods to the computer not to through codes for my swap which doesn't have things the F-Body does.)

It will run in the winter on winter blend 91 acceptably well, but not in summer, it'll ping. It's also EXTREMELY mild tune, something like 18 degrees total. The motor supposedly was "only" 11.1:1 or so, but it must be higher than that not to be tunable for 91. The previous owner ran an agressive tune on 50/50 race/stree gas. He had headers and an LS1 intake and I have stock manifolds and an LS6 intake. He made about 430WHP in his C5 and I make about 390 in my C3.

You ever think of running Torco?

[BRIAN]

As far as the car running rich when cool, I don't really see that as an issue since most modern cars have charge air temperature as one of the variables they monitor.
Gotcha, modern cars being 2000 up??

[BADDASSC6]

http://dagostinoracing.com/index.php?main_page=product_info&products_id=2175

Ben,
Call the guys up at cometic and see which head gasket would work for you. Their thickest gasket is .074 which would drop your compression ratio by almost .5. They are $89 each. Felpro makes some thicker head gaskets too. I did this on my old mustang. It was a 96 with 2001 heads and I need to drop the compression a bit due to the procharger.

The other options is to have some material removed from the bowl. Talk to Ron. They recommended speedomotiv for some port work I was interested in.

Other options are to get it tuned again by someone else. This will only help if the original tuner was bad.

Cheaper band aids:
I would try running colder plugs and see if Adam will let you borrow his wide band to make sure that there aren't any other issues causing you problems.

[BADDASSC6]

Gotcha, modern cars being 2000 up??

No like 94 and up. My 96 Mustang had it with OBD II.

[enkeivette]

http://dagostinoracing.com/index.php?main_page=product_info&products_id=2175

Ben,
Call the guys up at cometic and see which head gasket would work for you. Their thickest gasket is .074 which would drop your compression ratio by almost .5. They are $89 each. Felpro makes some thicker head gaskets too. I did this on my old mustang. It was a 96 with 2001 heads and I need to drop the compression a bit due to the procharger.

The other options is to have some material removed from the bowl. Talk to Ron. They recommended speedomotiv for some port work I was interested in.

Other options are to get it tuned again by someone else. This will only help if the original tuner was bad.

Cheaper band aids:
I would try running colder plugs and see if Adam will let you borrow his wide band to make sure that there aren't any other issues causing you problems.

:iagree:

Dropped my CR 4/10ths with a .61 Fel Pro MLS. They are also reusable, I'm on my second use.

[enkeivette]

While you're at it install some 1.7 or 1.8 (whatever you LS guys use) rockers to compensate for the hp loss.

[BADDASSC6]

I honestly think he will make more power. one of two thing is going on here:

1) his compression is much higher than 11:1

or

2) There is another problem that hasn't been diagnosed

If it's number one than the reduction in compression will allow him to get more aggressive with the timing. This will make up for the loss.

Ben do you have a OBD scanner? You could keep if in your car and see if it throws any codes when it starts detonating. What have you done so far to eliminate the common culprits?

[SeanPlunk]

I honestly think he will make more power. one of two thing is going on here:

1) his compression is much higher than 11:1

or

2) There is another problem that hasn't been diagnosed

If it's number one than the reduction in compression will allow him to get more aggressive with the timing. This will make up for the loss.

Ben do you have a OBD scanner? You could keep if in your car and see if it throws any codes when it starts detonating. What have you done so far to eliminate the common culprits?

I agree. Ben, I think you should take the car to CMS and have Ryne re-tune it.

[Vettezuki]

Thanks for all the tips guys.

Damian,
I do run Torco and with it it's totally fine. I could crank up the timing.

Adam,
Stock rocker ratio is 1.7. I pass smog just fine, but my cam, while mild, is about as big as I can go before running into trouble. Changing rockers effectively changes duration right? I am afraid changing rocker ratio may cause a sniffer problem.:huh:

Carlos,
I've definitely thought about the cometic. My suspicion is that CR is indeed substantially higher than the advertised 11:1, hence the reason I can't run any timing at all. Of course with a lil Torco, I could keep that higher CR and crank up the timing and it should make more than if I dropped the CR and turned up the timing right?

[Vettezuki]

Thanks for all the tips guys.

Damian,
I do run Torco and with it it's totally fine. I could crank up the timing.

Adam,
Stock rocker ratio is 1.7. I pass smog just fine, but my cam, while mild, is about as big as I can go before running into trouble. Changing rockers effectively changes duration right? I am afraid changing rocker ratio may cause a sniffer problem.:huh:

Carlos,
I've definitely thought about the cometic. My suspicion is that CR is indeed substantially higher than the advertised 11:1, hence the reason I can't run any timing at all. Of course with a lil Torco, I could keep that higher CR and crank up the timing and it should make more than if I dropped the CR and turned up the timing right?


I run Torco to make the ping problem never appear. I run 1 quart per 15 gal of 91, which is supposedly the equivalent of 93. I believe it because I mixed Toluene before that and it came out to the same result for the same output 93. Of course I have no idea how much timing I could put back in before the problem would reappear. If I'm at 18 total (my recollection) could I get to 30-34 with the mix I run? I don't know. I'm willing to run 1 quart per tank, but not more.

[enkeivette]

Benihana, you think too much. Thicker HG = lower comp = 91 only. :thumbs_up:

1.8 rockers = more lift = vroom vroom. Duration is changed minimally. I can do the math if you give me the specs, I think. You can also have them run it without any paper work just to see if it will pass before you take it in for reals.

[Damian]

It would be so nice to be able to hook up a laptop and see whats going on. The only thing Id try is running colder plugs. its a very cheap and easy try at fixing the problem. Are you OBDI or OBDII by any chance?

[Vettezuki]

It would be so nice to be able to hook up a laptop and see whats going on. The only thing Id try is running colder plugs. its a very cheap and easy try at fixing the problem. Are you OBDI or OBDII by any chance?

ODBII. I ordered some cheapy copper colder plugs.

[Vettezuki]

Benihana, you think too much. Thicker HG = lower comp = 91 only. :thumbs_up:

1.8 rockers = more lift = vroom vroom. Duration is changed minimally. I can do the math if you give me the specs, I think. You can also have them run it without any paper work just to see if it will pass before you take it in for reals.

So the official Adam recommendation is:

Cometic HG drop CR
1.8 Rockers
Retune

?

If I pull the heads, I can also install the set of nifty sodium filled valves I have. Right now I'm 99% sure it still has the truck head valves (remember, these are 4.8L truck heads), which are not sodium filled, so they're a bit heavier and retain more heat.

[BRUTAL64]

Brutal got it right for the most part.


I kept it simple. You know how Vettezuki is:inout:

[enkeivette]

So the official Adam recommendation is:

Cometic HG drop CR
1.8 Rockers
Retune

?

If I pull the heads, I can also install the set of nifty sodium filled valves I have. Right now I'm 99% sure it still has the truck head valves (remember, these are 4.8L truck heads), which are not sodium filled, so they're a bit heavier and retain more heat.

I think C6 made the recommendation first, but yeah. FelPro or Cometic, whatever is right for what you need. Then buy some used 1.8 rockers and see if it'll pass.

Don't know if you really need another dyno re-tune, I'd just pull the AFR down lower. If I remember right your motor was stoich at WOT. I'd bring it down a point or two, should help the ping prob.

Drop the CR 1/2 a point, colder plugs, more gas in the mix... should run on 91 all day. If you care about that sort of thing. I would def bet the plug fouling was a result of the Torco.

[94cobra69ss396]

Ben, do you know how much lift your valve springs can take? How about your piston to valve clearance? I wouldn't go installing a set of 1.8 rockers until you know these measurements. If you’re going to replace the head gaskets with thicker ones then you'll gain some piston to valve clearance over what you have currently but you will still want to clay the piston and make sure.

[Vettezuki]

I think C6 made the recommendation first, but yeah. FelPro or Cometic, whatever is right for what you need. Then buy some used 1.8 rockers and see if it'll pass.

Don't know if you really need another dyno re-tune, I'd just pull the AFR down lower. If I remember right your motor was stoich at WOT. I'd bring it down a point or two, should help the ping prob.

Drop the CR 1/2 a point, colder plugs, more gas in the mix... should run on 91 all day. If you care about that sort of thing. I would def bet the plug fouling was a result of the Torco.

FYI, current tune equals:

http://motorgen.com/pic/data/515/BirdRunDyno1.jpg

[Vettezuki]

Ben, do you know how much lift your valve springs can take? How about your piston to valve clearance? I wouldn't go installing a set of 1.8 rockers until you know these measurements. If you’re going to replace the head gaskets with thicker ones then you'll gain some piston to valve clearance over what you have currently but you will still want to clay the piston and make sure.

Thanks for the warning. These are comp cam springs, and I *think* they're good for beyond .600 lift, but not positive on the specs.

[Vettezuki]

You guys keep forgetting about quench. Yep, that'll bite you in the ass. Quench should be around .045. Much bigger than that and you're right back to pre-ingition with your lower compression. :drink:

I don't see where that plug was fouled. It had a lot crap on it, but that didn't mean it wasn't firing. I'd have to look at that plug close up. To be sure.:)

I forgot, what's quench again? I'll bring the plugs with me this Saturday. I already ordered a set of copper autolites on the colder end of the spectrum.

[Vettezuki]

BTW, if I'm running a stock stat, what should I consider going down to???

[BRUTAL64]

BTW, if I'm running a stock stat, what should I consider going down to???

Hypertech set their computer chips up for 160 degree stat. Seems like a good temp to me.:p