*Could someone give me straight story on the impact of lower thermostats & mileage

[>>>>head]

fellow junkies
I recently picked up my LS2 GTO from the shop that rebuilt the motor (1,500 miles ago). Basically the motor is fresh (new pistons, rods, cam, bearings, oil pump, rebuilt heads, etc). I told the builder that the primary purpose of the Goat was being a daily driver.

When I went to pick up the car the builder told me he installed a 160 degree thermostat. I was under the impression that a lower thermostat hurt mileage if for no other reason then it keeps the motor in an open loop condition longer. Furthermore, it loads the cats with fuel which helps shorten their life. I suspect the builder wanted the lower thermostat to help the dyno numbers. My mileage is definitely lower (4-5 mpg) but I am not sure how much that is due to a fresh engine.

So what is the story with lower T-stats on modern, computer controlled engines?
Thanks








8888888

[Barry Donovan]

it is about thermal dissipation.

An 8 cyl is an easy one to judge by mechanics who have been around them.

headers, wrapped not wrapped, radiator material.

size of engine bay.

if you refer to new gto, the FWD looknig chassis. I'd be going 160 too...ECU or not. they aren't a miracle.

[Scott Liggett]

The LS engines are built with tight clearances that the engines literally pick up power as they loosen up after 50k miles. It is not out of the question that it will cost mpg to move a tighter engine.

If your engine and its tune are set up for the factory 195 thermostat, it could be effecting the mpg too. You can tune for max power or max mpg, but mostly you have to find a comprimise.

[squirrel]

I know a cheap way to find out. Put the correct thermostat in, and see how it does on gas.

In a DD, I really see no advantage to a colder thermostat. I run 180 or 195 in my old rides.

[milner351]

I'm not sure why he would have put a 160 in it unless he's afraid of it running hot.

I don't see why a relatively stock engine in a car it was designed for with relatively new components would need a 160 tstat.

I'm sure if that was a GM rebuilt engine going in at the dealer - it would have a 195 tstat.

[DanStokes]

I'm with John on this one (but then I USUALLY agree with John!). I'm guessing the mechanic was Old School and probably thought he was doing you a favor. If the engine runs hot with a 195 there's something wrong - bad rad, cooling fan issue, or the engine wasn't assembled correctly.

Dan

[anotheridiot]

we used to leave thermostats out unless we were worried about winter heat. if its an LS engine, the intake is sealed off from the block so there is no heat transfer to rob power from your air fuel charge. I had a 97 lumina and a 98 malibu, both with the 3.1. The cooling fan never comes on the malibu, the fan is on within minutes on the lumina. with all the fuel changes the computer does to actually cool the block, you figure that 160 is just gonna let that coolant circulate all the time regardless of the fan. Just figure that fuel is gonna burn less efficiently in a cooler block and end up with lower mileage.

Dont really have an answer, just some ideas why he might have done that.

[Scott Liggett]

Back in the 80's during the 350 TPI days, shoving a 160 thermostat increased power. You were able to increase the hp by a percentage for every 10* cooler you could get your engine to run. This was also the era when they discovered running the engines at a hotter temp lowered emissions. That was when 220* running temps became norm.

Of course, running a engine that cool, you would get piston slap because they didn't get hot enough to expand to their correct size.

[dieselgeek]

If the ECU wasn't retuned for it, you should put the OEM rated T-stat back in before you ruin more than a set of cats. Running around in Warmup Enrichment is not good for a lot of things.

[DanStokes]

THERE'S your answer. Scott LIVES this stuff.

Dan

[>>>>head]

Thanks for your feedback. After reading your thoughts & then talking to the builder, I am leaving the 160 T-stat. With ~ 1,800 miles, 2 oil changes and replacing the cats, the mpg is close to her old numbers

[OldMachinist]

You asked for advice and got it from DG who I assure you is more knowledgable than your engine builder. Install an AFR gauge and if you are using a stock ecm it should read 14.7-1 with the engine at operating temp.