160* thermo change or keep?

[phenomic]

I have a 97 z28 lt1 camaro with 113k miles on it. I believe it ahs a 160* thermostat because it is a common modification, the guy i bought the car from said something about he changed the thermostat to lower temps. It came with a hypertech reprogrammer that can advance timings or something and other stuff and it recommends the thermostat. I dont have the advanced timings or anything enabled right now but i could do it.

Its turning to the winter and i heard the 160 is too low from the stock 180 i believe. My temp gauge says that the car is running at about 170. It stays pretty consistent at that unless i rev it up for a while during idleing.

I am wondering if this little drop in coolant temperature is hurting my gas mileage because i am only getting about 13mpg at the time with a full tuneup (my distributer may be going and my o2 sensors could be causing this as well).

 

[7TFord]

Yes! If you're running too low an operating temp then your gas mileage will suffer. So does engine wear. An engine will have increased wear if not run at the correct operating temp even in summer. If the engine oil doesn't reach a certain temp also there is an increased chance of sludge formation.

 

[phenomic]

I see exactly what you mean and i understand it as well. I noticed almost everyone who has an upgraded lt1 on some other forums seems to have the 160 stat thermometer. My car came with it so ill look around. It seems to be a commong modification so i was wondering what i should do?

 

[Marlin]

A 160 stat is BAD for most F/I cars. If the temp stays to low the computer will not go into loop mode and keep running at a set stream as it thinks it is still warming up.

The lowest I would go is 180. Warm enough to get the computer thinking, but stays cools enough to make some power. That factory temp should be 195. So even 180 is a decent drop, but 160 is way to much.

 

[wileyE]

The 160 just fools the manifold coolant temp sensor into thinking it cold and needs more fuel and timing, thus slighlt more power (not always though). Better to run the stock stat and fool the sensor with a resistor if you want to play around with it.

I had a tranny guy tell me that he loves the hot coolant temps the new cars run. It's good for business.

 

[kevm14]

quote:

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Originally posted by Marlin:
A 160 stat is BAD for most F/I cars. If the temp stays to low the computer will not go into loop mode and keep running at a set stream as it thinks it is still warming up.

The lowest I would go is 180. Warm enough to get the computer thinking, but stays cools enough to make some power. That factory temp should be 195. So even 180 is a decent drop, but 160 is way to much.

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Pretty much all cars these days have heated O2 sensors. My Caprice does not. Yet, in the ECM calibration, the min temp for closed loop is 123*F coolant temp. If my Caprice can hit closed loop that cold with an unheated O2 sensor, a car with a heated one can probably do closed loop as soon as it feels like it (usually after some timer expires).

LT1s use a 180* stat as stock. But with the reverse flow cooling, that means coolant is entering the head at 180. By the time it comes out of the block, it's around 195*. A 160 stat in these cars will leave you with 170-175* coolant temps. Still, I don't really like colder than stock stats. Oil temps are an issue and so is efficiency. 195*F is a pretty efficient range. BSFC goes up as coolant temps go down.

quote:

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The 160 just fools the manifold coolant temp sensor into thinking it cold

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There's no fooling, it really is that temp. And as temp goes down, required spark advance goes up, because, again, the engine is less efficient, so the burn needs to be started sooner in the compression stroke. One of the primary reasons cars may accelerate faster with colder stats is because the intake air temp is decreased. Colder air = a denser charge (more O2 per volume). But on LT1s, the intake manifold is not water cooled, so there is less of a reason to run a cold stat, imo. My LT1 has the stock stat and I intend to keep it that way.

 

[Ryan00TJ]

On my H/C LS1 I run a 160 stat during spring and summer and actually just changed it back to stock a few mins ago for wintertime. I am running ported Stage II 5.3L heads at 10.8-1 Compression and during those hot summer days the IAT's can get pretty hot especially after a few track runs. It's a good mod to have during the summer. For winter it needs to be taken out as it keeps the motor too cool. MHO

 

[clutcher]

Yup, I have to agree with Marlin. On OBDII vehicles closed loop starts at approx. 195 degrees. Running around in open loop just wastes fuel. In California when we have a 4.0 OHV Explorer (thermostats always stick open) and we try to smog them they fail the smog test due to elevated emissions. The vehicle is not very efficient at that stage. We install a new thermostat, verify approx 193 degrees, closed loop, reset keep a live memory (KAM) and perform readiness tests (OBDII drive cycle), retest the vehicle and it comes through with flying colors. Our customers usually state that the vehilce runs better too. Those car were designed to burn lean and clean. There are other ways to gain horsepower (chip, cat back systems, and intake).

 

[454MAG]

Specifically speaking about the LT1 motor the 160 degree stat is a good thing. This motor becomes a real dog when it gets hot -- over 200deg. Timing is retarded and knock and resultant timing retard occur. This is a fairly high compression engine at 10.5 to 1. Also the tranny seems to shift sooner making thins seem even slower. I have a 94 formula with the LT1 with 205k mi. I have kept the 160 stat in since 48k. When I replaced the water pump at around 180k I thought I left a plug wire off or something-- It was the 180deg stat that comes in the pump. I quickly pulled it out and performance came back. The LT-1 really likes cooler temps. I do mostly highway driving so the stat controls the temp more than the fan control switch but even in hot weather stop and go traffic you start out 20 deg cooler. Also plenty of heat in the winter.

 

[kevm14]

quote:

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Originally posted by clutcher:
On OBDII vehicles closed loop starts at approx. 195 degrees.

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Uh, no. There is nothing special about OBD-II vehicles that would allow you to make a (wrong) blanket statement like that. If anything, OBD-II would want to enter closed loop even sooner than OBD-I, since there is constantly pressure to light the cat off sooner as the years pass (cats need a 14.7:1 air/fuel ratio to work properly, and you can guarantee this only in closed loop mode).

 

[clutcher]

I monitored the live data on a 99 Explorer today and found closed loop started at 192 degrees. OBDII requires that the onboard computer monitors and actively performs diagnostic tests on vehicle emission systems. It is much more sophisticated and supports more data than older OBDI systems. I spoke with 3 local Chevy smog mechanics and 2 Ford mechanics (all drivability techs-including myself) and we all agreed that closed loop starts for Ford at 188 to 193 degrees and GMC is 180 to 190 degrees. Although the Chevy guys did say that a 160 degree thermostat could give you a bit more zip, but it is not worth it when the time comes to have an annual emissions test. Also the car suffers from high under hood temperatures, According to the CA state smog inspection manual it states 190 degrees to verify closed loop operation.

 

[454MAG]

Phenomic

Just reread your original post. If your only getting 13 mpg there is something else seriously wrong. I consistently get 24.6 MPG hwy and around 20 around town driving hard with my lt1. This is with the 160 stat, 205k miles, cold air intake and cat back only.
It is probably time for an Optispark, plugs and wires. Be sure to change the water pump when you do the opti. Is the car throwing any codes ?

 

[phenomic]

I know something is wrong with my fuel usage. It is mostly short trips, high traffic, lots of stops. So i dont expect to get great gas mileage but im goin for 15-18.

I changed just about everything on my car (Fluids, filters, plugs, wires, brakes, some other stuff). Im trying to find the source. I believe my opti is going too like you said. I have 113k and i keep hearing people getting way better gas mileage. I am changing my water pump tomorrrow due to a small leak on the back and i got a 180 stat to go with the new pump (the leak may have killed the opti)