Alvin

This post is to reflect the experience I have learned first hand w/ SBC's and LT1's. No part of this information was gathered directly from another source. It is not intended to be a "God's Law" or "Final Conclusion" as there are many opinions on this subject.

Background
The optimal operation temperature of an engine is such to provide efficient combustion without excess heat scrubbing, to stay within the metallurgy limits of the internal components, and finally to prevent fuel/air charge to be near spontaneous combustion temperature after the compression stroke.

1. Efficient Combustion
Internal combustion engines work on the principle on releasing heat in fixed and ideally isobaric (constant pressure during power stroke) chamber to displace a piston.

When there is a temperature difference between to spots you have a potential difference for heat transfer to happen. So what this means is if you have heat flowing down hill all the time. In this case heat will flow out of the combustion chamber and into the heads, the block, the piston etc. This heat is now wasted energy and obviously if you have a greater difference between the combustion and engine/coolant temperature you will have a higher potential to waste more of this otherwise useful heat.

2. Metallurgy limits.

Very simple. We would love to run our engines at a very high temperature to reduce the "downhill" for the heat that we intend to do work with but unfortunately this isn't possible due to material limits. Those limits include thermal expansion and obviously ductility at high temperatures (this is the root of wearing) and melting point.
3. Heat exchange to fuel/air charge

During the compression process you create tons of heat. This heat is compiled with any heat scrubbed off the intake, head, and cylinder walls during the intake and compression strokes. If enough heat is transferred to the fuel/air charge you'll run into pre-ignition. This is very hard on a engine and definitely ruins performance.

On to real world.

The L98 typically calls for either a 195 or 190 degree thermostat from the factory. The LT1 calls for a 180 degree thermostat from the factory. What is the difference for?

The reason why is simple.
The difference is because LT1's thermostat controls water flowing into the engine whereas the L98 thermostat controls water flowing from the engine. Obviously there will be a hotter temperature leaving the engine than entering the engine so therefore appropriate temperature thermostats where chosen to deliver the desired engine operating temperature. *The change in temperature between the inlet and exit sides of the coolant WILL happen if any heat transfer took place.

My choices in thermostat.

For LT1 160 thermostat (180 operating temp)
For L98 180 degrees (slightly less than 200 degree operating temp)

Why? Well, because I've seen better results with those combos but I'll try to justify them here.

The L98 (and gen 3 and 4) uses a traditional SBC style cooling system. In this system coolant is sent to the block, then the heads, then the intake and finally back to the radiator. The LT1 uses a unique reverse-flow cooling system where coolant is first sent to the heads, never sent to the intake, then sent to the block and finally back to the radiator.

Remember #3 from above? Let the LT1 capitalize on the reverse flowing coolant system and try to keep a cool dense air charge into the engine by offering a cooler head temperature. We can do this without worrying about ruining number #1 because water entering the block is now warmer than what we allowed to entering the heads.

Why do I choose a 180 for the L98?
Because I have found it to be a nice fine balance between numbers 1 and 3 from above. It allows us to run a hotter tune in the engine, keep the efficiencies up, and gives us a little more wiggle room when it comes to the quality of fuel we use.

CFI-EFI

Interesting observations and opinions. I, for one, find no argument.

RACE ON!!!

OldCorvetteFan

Alvin -

Good post. I like the way you put together your rationale.

Steven

JackDidley

I agree on the L98 for sure. 10 years ago I had a Hyper chip and they said to use a 160*. Took forever to warm up in the cold weather and did not run any cooler in the summer. I have been using a 180* since then.

Alvin

Cool, Can it be a sticky?

STL94LT1

I vote for "sticky" and "locked", before the arguing starts.

vader86

I've asked for a thermostat sticky several times.

87 rag

Thanks Alvin,
It might be time for me to switch.

byebyeL98

Sticky! Let us never debate the subject again

TorchRedlt4man

I agree totally with your reasoning, Alvin!

Corvette Kid

Arguing, here?
Alvin, any thoughts on the 160 in an LT1 as it relates to fuel economy? Very well explained ideas, BTW.

CentralCoaster

Damn. He smartly dodged all the juicy points.

jfb

If you recommend a 180 stat for L98's and claim the coolant temp is slightly below 200, then the thermostat is wide open and it does not control the engine coolant temp. Except for warmup time, you might as well not even have a thermostat in your L98 because the L98 will run at the same temp as with the 180 stat. I use the recommended 195 stat in my 87 and above 35 mph, my coolant stays at 195 and the thermostat controls my coolant temperature. All of my previous cars used a mechanical fan, conventional coolant flow, and a 180 thermostat and the temp stayed at 180, even at stoplights in the summer. The 180 thermostat controlled the coolant temp because the radiator had excess heat ridding capacity even in high summertime temps. I think people ask about and use 160 stats because their previous cars too stayed at the stat opening temp and they think their C4 would do the same if they used a lower opening temp stat. The higher temps in C4's than previous experience with past cars cause concern because whenever I saw my temp exceed 180 in previous cars, I knew I had some kind of cooling problem. The point I have always made in C4 160 stat posts is that a lower opening temp stat will not necessarily provide a lower coolant temp. In the winter, when the radiator has much higher heat ridding capacity, your cooling sytem may run at the opening temp, and 160 F is too low for engines. C4's have radiators sized to maintain 195 coolant temps above 35 mph and (from my experience) air temps up to 90 F. Even at 90 F and idling with the a/c on, L98's don't run dangerous coolant temps. GM says in owners manuals to shut the engine off at 260 F and let it cool off. Except when I had a bad head gasket leak, I have never seen 260 F in my 87 vette and I have the original engine with 209k miles and I drive it everyday in every kind of weather. In future posts about 160 stats installed with claims that the coolant temp runs higher than 160 F but lower than the 180-195 stat, you can expect to see me there still trying to explain that if both stats are wide open, then the operating temp must be the same.

Aardwolf

180° is working wonderfully in my L98.

jeff32463

My 88 has run much better since I switched to the 180* stat. Better consistent throttle response. Just my novice opinion.

Steel Breeze

It is a delicate dance we do, because of so many variables. Weather, fan on of temps, outside ambient air temps, and etc... I think like Alvin, around 200* most of the time. The high heat situation that GM engineered into our cars for emission control, is just plain to hot IMO. Heat like that eats up alternators, wiring etc. The alternator usually has 2 cooling fans. 1 for the diodes, the other for the stator, and rotor. Imagine your alternator trying to cool when all it has to pull through the fans is 230* air. Don't count out the poor bearings either. Reason for all this alt. talk, is I just rebuilt mine, and could see the effects of high heat on the internals. Example: 2 out of the six 50 amp diodes had been hot enough they were all bubbled, they checked ok, but I bought a new set. No way was I running those... My .02.

Corvette Kid

Heat is the big killer of alternators. That's why they're generally larger, the higher the amp rating, to better dissipate the heat. Many manufacturers tried smaller, high amp ones but most went back to a larger case where practical because of reliability problems. Anyhow, I digress. As usual, good insight Steel Breeze, on yet another good reason to moderate temps.
Since I've installed the new and larger engine, I've been on a quest to diminsh underhood temps. And of course part of this is obviously better controlling and regulating engine temps. Although coolant temps are only up slightly, oil temps are up a bit more than that. And one thing I never before considered in dismissing the 160 stat for LTx engines was the reverse flow. I long ago quit reading and responding to these threads because it was something I was tired of arguing about. But oddly enough I was looking at the engine and thinking about this just the other evening, while replacing the remainder of the coolant hoses on my car that I hadn't already replaced. Then I saw this thread. And since it was by Alvin, I decided to give it a read. I'll be visiting my daughter next week. Her husband works for Jegs. I'll have him pick me up a Hypertech stat (at his discount) and I'm going to give it a try. Damn shame if it works, I just got done installing a new GM one with the new engine!

sami85L98

damn, i just replaced 160* yesterday, previously had 180*. have to drive today to see actual diff. Drove last night for 5-6 miles after replaced. Temp stays between 179-183 w/160*, and previously with 180* temp stays 183-195 only in night time driving.

Make this sticky.

rick lambert

Nice...well thought out post Alvin I'm actually pro 180 in the L98 and anti 160 in the L98....don't know anything about the LTs, so I don't comment. I think however, if we get the desired running temps of around 180 it really doesn't matter which.

STL94LT1

OK, here's something else to look at when running a 160* stat in an LT1. On a cool day I will see ~176* on my digital temperature gauge. But, 185* on my analog gauge. The digital gauge measures the coolant temp entering the engine, and the analog gauge measures the actual engine coolant temps. So, to me even if the digital gauge says 176*, the engine is really running 185*.