Benefits & Disadvantages of various temp thermostats on engine performance

[Chris 96 WS6]

I'm going to try to define the question well enough that it fits the "high-end" discussion parameters for this forum.

Last week I failed emissions testing, my hydrocarbons were twice the allowable limit of 220. I think I have it were it will pass now thanks to some idle timing adjustments and putting the stock thermostat back in.

But that's not my main point....this whole thing got me thinking about ideal engine operating temperatures and what you give up at each temperature.

So what are the ideal temperatures you want to see in an engine? LT1's are reverse cooled of course, so the heads see the coolant first and are thus cooler with the 180 stat than a typical Gen I with a stock 195er.

So then, a 160 stat in an LT1 would put those temperatures even lower. Any adverse effects on oil temperatures?

A hotter combustion chamber produces a more complete burn, right? (to a point, of course, too hot produces preignition). Yet a hotter overall operating temperature increases heat soak and increases air intake temps, reducing the total HP potential of the intake charge. A cooler chamber can tolerate more timing advance, but if the burn is incomplete, is there any advantage? Is there any justification for splitting the difference, say, 170?

I'd like to see some in depth disscussion here. What's preferrable, what produces more power, what produces better longevity, etc. etc.?

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1996 Trans Am WS6, A4, GTP Stage I heads, CC 304 cam (210/220 .500/.510 114LS), Comp 1.6 ratio Pro Magnum roller rockers, FLP long-tube headers, Flowtech cutout, Dynomax Ultraflow muffler PN# 17227, BMR rubber/poly tubular LCAs, Lakewood adj. PHR, LT1 Edit for OBDII, LT4KM, 52mm TB.
Member of MTFBA (Middle Tennessee F-Body Association)
10/27/01: 13.22@106 w/2.1 60ft and lots of KR.

[Tab92bird]

I'm pretty curious on that subject myself...which is part of the reason I haven't gotten a lower temp one.

ttt

[Mr. Horsepower]

<font face="Verdana, Arial" size="2">Originally posted by Chris 96 WS6:
I'm going to try to define the question well enough that it fits the "high-end" discussion parameters for this forum.

Last week I failed emissions testing, my hydrocarbons were twice the allowable limit of 220. I think I have it were it will pass now thanks to some idle timing adjustments and putting the stock thermostat back in.

But that's not my main point....this whole thing got me thinking about ideal engine operating temperatures and what you give up at each temperature.

So what are the ideal temperatures you want to see in an engine? LT1's are reverse cooled of course, so the heads see the coolant first and are thus cooler with the 180 stat than a typical Gen I with a stock 195er.

So then, a 160 stat in an LT1 would put those temperatures even lower. Any adverse effects on oil temperatures?

A hotter combustion chamber produces a more complete burn, right? (to a point, of course, too hot produces preignition). Yet a hotter overall operating temperature increases heat soak and increases air intake temps, reducing the total HP potential of the intake charge. A cooler chamber can tolerate more timing advance, but if the burn is incomplete, is there any advantage? Is there any justification for splitting the difference, say, 170?

I'd like to see some in depth disscussion here. What's preferrable, what produces more power, what produces better longevity, etc. etc.?

</font>

Chris, this is an excellent question. I'm doing my typical run through the forum as there are some threads I've neglected for lack of time. I'll answer this question sometime this week. I'd like to get some of my notes and show you some of the differences we've seen in many of our tests, so I'd like to put down some hard numbers. Alot of theory too.

Take care,
Chuck

[Soma07]

That would be great Chuck! I've always wanted to see some hard numbers on the thermostat issue.

I know my car seems to run faster when its cooler but I'd also like to know why

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Jason
93 TA, M6

[TrannyGuy]

The lower thermostat thing has always been a puzzle to me. I've heard too many differnt things about it. For one someone once told me that if you want your engine to run cooler you put a higher temp thermostat in it like if your car has a 180 stock you run a 190 and it will run cooler. That makes absoulutly no sense to me but the logic behind that was that since the thermostat won't open as soon the coolant in the radiator gets more time to cool thus doing a better job of lowering combustions temps. That seems logical to me, for some reason I can't agree with it, even though i've heard many people say it's true. To me it just makes more sense that if you had a colder thermostat like 170 instead of 180 that your thermostat would open sooner and recirculate quiker to keep a lower temp. I'm still not sure which one is correct yet. As far as you failing for hydrocarbons... The thermostat is really going to have more of an effect on nox, because nox forms at high temperatures. Hydrocarbons is the result of unburned gasoline, which could mean a few different things. Too rich mixtures too lean mixtures, bad catylitic converter, bad ignition system, etc etc. I wouldn't suspect engine operating temperature as an issue unless your normal coolant temp was never getting hot enough for your vehicle to go in close loop which would in turn make your car run rich, which may also make people believe that lower coolant temps make their car faster when in fact it's only because their car is running richer since it never reached close loop. I'm just trying to think of an explanation, not sure if this is true.

[Chris 96 WS6]

Thanks Chuck, look forward to reading your comments.

I've heard of the 160 not allowing the oil to get hot enough to boil out water, leading to bearing damage in the long term, but I think the guy swapped it back out before anything adverse happened. I don't think that's the norm, but its certainly something we've never heard a definitive answer on.

The ultimate goal would be to get the engine nice and hot but maintain a cold intake air charge. There is definitely a balance, and I remember watching NASCAR Winston Cup last year and Larry McReynolds commenting on the ideal temps they like to see for coolant and engine oil. Whatever those temps are (don't remember exactly what he said), would be the goals, and I wonder which temp thermo gets you closer to those values?

[Camaro73]

I like the LS1's approach... composite intake= cooler intake= more power.

If I could get my engine to run at about 195 degrees, yet keep the intake manifold cool, and the inlet air temperatures down, I'm in good shape.

Alas, the aftermarket hasn't jumped on this yet.

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John
'71 Camaro
350, 4 bolt, 212/218@.050", Edelbrock RPM heads, 3.42 posi, blah blah blah

I wanted to bring this back to the top in the hopes that Chuck would post his comments.

[Steve in Seattle]

<font face="Verdana, Arial" size="2">Originally posted by Chris 96 WS6:
I've heard of the 160 not allowing the oil to get hot enough to boil out water, leading to bearing damage in the long term, but I think the guy swapped it back out before anything adverse happened.</font>

hmmm... you have a point about the water not boiling out. since the water and oil don't combine, the water would retain its own vapor pressure (boiling point) separate from the oil.

If the water's from a coolant leak, I dont' think you'd be able to evaporate it out anyway... the coolant has already raised the boiling point beyond even stock thermostat temps. Besides, at that point you've got worse things to worry about.

If the water's from condensation inside the crank case and engine, yeah you may be able to validate that. But I'd be aweful curious to see the accumulation rate of moisture in a daily driven engine vs the oil-changing frequency.

Anyone have some numbers to post regarding % water content in oil they recently had analyzed? (say after 3000 miles or so)?

If you neglete oil changes, accumlation may be an issue, but again, you'd have worse things to worry about damaging your engine if you try to pull a Mobil 1 "reccomended" 15,000 mile oil change.

I'd bet the dirt and metal would kill you faster than the water contect.

BTW, this may be a good theoretical discussion, but my baby's been running a 160* stat for 30,000 miles (of 107,000 total) and still runs like a champ. I've seen the gains on my 70 mile commute each day, and wouldn't go back to stock unless Chuck SWORE it'll blow up my engine at 150,000. (the goal is to run this baby to 200,000 miles without a rebuild ).

[rskrause]

<font face="Verdana, Arial" size="2">Originally posted by Steve in Seattle:
hmmm... you have a point about the water not boiling out. since the water and oil don't combine, the water would retain its own vapor pressure (boiling point) separate from the oil.

If the water's from a coolant leak, I dont' think you'd be able to evaporate it out anyway... the coolant has already raised the boiling point beyond even stock thermostat temps. Besides, at that point you've got worse things to worry about.

If the water's from condensation inside the crank case and engine, yeah you may be able to validate that. But I'd be aweful curious to see the accumulation rate of moisture in a daily driven engine vs the oil-changing frequency.

Anyone have some numbers to post regarding % water content in oil they recently had analyzed? (say after 3000 miles or so)?

If you neglete oil changes, accumlation may be an issue, but again, you'd have worse things to worry about damaging your engine if you try to pull a Mobil 1 "reccomended" 15,000 mile oil change.

I'd bet the dirt and metal would kill you faster than the water contect.

BTW, this may be a good theoretical discussion, but my baby's been running a 160* stat for 30,000 miles (of 107,000 total) and still runs like a champ. I've seen the gains on my 70 mile commute each day, and wouldn't go back to stock unless Chuck SWORE it'll blow up my engine at 150,000. (the goal is to run this baby to 200,000 miles without a rebuild ).</font>

Oil gets a lot hotter than the coolant.

Rich Krause

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'95 Z-28 383 with Vortech, NX kit, etc.
"1FASTZ28"

[Chris 96 WS6]

The primary questions I'd like to see answered are these:

1) Does a 160 stat in an LT1 allow proper combustion chamber temps to be reached? e.g. there is such a thing as too cool a chamber.

2) Ideal oil temp is somewhere around 210-220, right? What is the 160's effect on this.

If I were running a 160 in a gen I small block my concerns would be somewhat different. Since the heads receive the coolant last in a traditional small block, I'd be less concerned about chamber temps and even more concerned about insufficient oil temps. I ran a 180 in my old '85 Camaro and thought it was more than sufficient...I don't think I'd run a 160 in a Gen I.

[Steve in Seattle]

My understanding of the oil/coolant temp relationship is that oil is typically ~30*F higher than the coolant in the engine.

A 160*stat, running coolant at ~170*F would corrospond with engine oil being at ~200*F. (which is below the pure boiling point of water, not that it matters if you change your oil ).

Considering the mutigrade oils avilable, I'm not so sure you'll see any difference between 15*F change. Especially since its only at cruising temps that anything's affected. stop and go driving has the engine temps get to the same level eventually (the 165 to 180 zone is the only difference).

[wile2k]

<font face="Verdana, Arial" size="2">Originally posted by Mr. Horsepower:
Chris, this is an excellent question. I'm doing my typical run through the forum as there are some threads I've neglected for lack of time. I'll answer this question sometime this week. I'd like to get some of my notes and show you some of the differences we've seen in many of our tests, so I'd like to put down some hard numbers. Alot of theory too.

Take care,
Chuck



</font>

Chuck, can't wait. Then we can just post a link to this post under that huge discussion (argument? ) going on in LT1 tech. Thanks for lending the knowledge.

[Chris 96 WS6]

Still waiting eagerly for Chucks input

[MadMax350]

Here is the deal with engine temps. First of all, water will vaporize at any point above freezing. You don't have to have the water boil out of the oil, it will do it anyway. Your engine oil is formulated to take this into account and prevent the buildup of acids caused by oil-water contamination within its normal usage life. Afterall, how hot does the oil get in your lawnmower?

I don't think the moisture in the oil should be the biggest concern here.

The biggest concern sould be on cylinder wear. It has been proven time and time again that too cold of a thermostat will cause stock engine failure. This is due to the stock engine pistons and rings being designed to run with a 195 or 180 theromstat (depending on what came stock). Someone I knew put a 160 stat into his 94 Z and now wonders why he has serious blow-by just a year later. The damage comes from the piston's and cylinder wall's abaility to transfer heat and the difference between the two materials. If you put a 160 stat into a stock (lower ended) engine, you will scoar the cylinder walls. This happens because the pistons are not expanding to their "designed" size and this, in turn, puts more stress on the piston rings. You can rebuild your engine using better materials for the pistons and rings and run tighter clearances that will last longer under a 160 stat if you choose. It just depends on how much it is worth to you. I don't think the minute gains you get from using a 160 stat are worth it.

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1987 Trans Am GTA WS6
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1987 Pontiac Fiero
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1988 Pontiac Grand Am
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1966 Plymouth Belvedere II
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http://dtcc.cz28.com

[This message has been edited by MadMax350 (edited February 12, 2002).]