I have done a search and read over 100 threads on this topic and hear a lot of conflicting answers to the question, "what temp of thermostat should I run?" I am somewhat on the fence too. After consulting with a well known race shop who builds alot of fuel injected motors for street, race and marine, passed me a short paragraph when people ask them this same question and to draw my own conclusions:

"coolant tempeture has a pronounced effect on performance....Both air/fuel ratio and ignition timing are altered depending upon coolant temperature. Lower temperatures result in RICHER MIXTURES AND MORE AGGRESSIVE SPARK TIMING. High temps have the OPPOSITE EFFECT."

Now it didn't say at what low and high temps this takes place and what the optimum temp is but for me this says 160 will perform better than 195. Yes mpg will go down but performance will go up, there is always a trade off. As far as more wear and tear with running lower coolant temps the race shop said they have seen no hard evidence that points to this.

 

I run a 180 in my 400 when it does street duty.

And to a point, engine performance goes down if the engine is running too cold (enter the theories of heat transfer here).

 

I run a 180 in 91 TPI Z and a 87 TPI GTA
I also run a fan switch that comes ON at 189 degress . Car makes closed loop no problems.
Also I change the tranny fuild to synthetic and change the filter.
Now that the engine is much cooler (fan did come on at 220) the 700R4 will last. The excessive heat cooks the trannys in these cars and that is the fix.
Also make CERTAIN your under car aid dam isnt damaged.
Ill get the part number for the temp cooling switch for the pass side head if anyone wants.

 

I installed a 170 degree thermostat in mine, available at your local GM dealer, although not a usual stock item so it had to be ordered. # is 10220957
I have had it installed for quite some time now. I have noticed no ill affects with gas mileage,,,I actually just checked it the other day,,,,all city driving with no highway and I got 19.4 mpg with an 88 Iroc with the 350 TPI (L98) and the last highway trip I made about a month ago it got 26.2 mpg.
My biggest gripe is the fans come on too late. I changed the temp switch in the head to turn on the second fan sooner, but the lowest temp switch I could find was the Hypertech and it doesn't come on until 200 degrees and shuts off at 185.
I would rather see it come on around 190 degrees and shut off around 175.
The main fan is controlled by the computer and comes on around 220 so I will have to reprogram to change that.
Formulabruce, I am interested in what your on/off temps are on that switch you have. I would like a part number if possible.
I also agree, everything else runs cooler as a result, not just the engine, I also have better A/C performance, it cools the car down much faster than before, trans temps are also critical, the cooler the better in my opinion. I run cool thermostats in ever car I own, have been doing it for over 20 years with no problems.
I read another post about grounding the fan relay with a switch to have the fans run when wanted and still retain the stock functions,,,,thats a nice idea too,,,if I only knew which relays controlled a factory dual fan setup Too many freakin relays on this car,,,,Grrrrrr Larry.

 

on at 189 , off I think is 175
I have done extensive research on these and the one I use is small and has a wire and a small sleeve it threads in.
I dont have the info here at work, I will get ya the number tomorrow with a pic
I was able to put in a 180 (had a 170 like yourself) and it runs better, rather it seems more closely controlled with the 180 and this particular switch.
one fan is green wire controlled, to ground, the other is A/C and temp overload computer controlled but can be grounded as well.
If you do what I do, it will not be needed

 

On my car (see sig) there are two relays. the one on the rad support on the passenger side is the primary (run by ECM). The second is on the passenger side next to the evap canister (run by temp switch in the block). Just run a connection from the green/white wire,at the second relay, to a switch. then a wire to ground from the switch.

now your off and running

 

Thanks guys,,,,,I am with ya Formulabruce, I am hoping that once I reprogram the computer and adjust that fan to a temp of my liking, and possibly have the second fan come on a little sooner with a different switch in the cylinder head, that I won't need to run a toggle switch to the relay,,,,

Thanks Roads88,,,I will look for those tonight,,,I should know where they are anyway for piece of mind in case one ever quits out on the road,,,probably a good idea to carry some spares in the car for emergencies. Thanks again,,,Larry.

 

With a lower temp fan switch you will not need the toggle. I removed mine.

the switch is just a bitch to get at with headers.

 

FYI the fan switch I run is a echlin part, get it at NAPA, you may see it on their website, use the search on left and punch in that part number.
its got a long sensor, and its a 1/4 pipe thread, so I use an adapter that amounts to a sleave and install in the pass side head, yeah its a pain.
with a 180 T stat you will never need a switch if your radiator is in good order.
part number #FS158

on at 189 degrees
off around 181 Thats a guess, as I dont have the exact OFF number.
keeps her cool and my tranny loves me again

ps youll need a end (also at napa) to make the connector snap into the harness, the one it comes with is male since it has a short wire. price is a bit steep at 44.99 still worth it

 

hypertech makes an on/off switch for 176/166 to be used with a 160 stat

 

Ya thanks Don, I am aware of that Hypertech switch, it's just not the right temps to work with my 170 stat. And the Hypertech switch I have doesn't come on until 200 which is higher than I like,,,,it shuts off at 185 which isn't low enough for my liking, and Hypertech doesn't make anything in between Thanks though.
Thanks also Formulabruce for that part number,,,I will check that out for sure. If I can get both of these fans to come on and off when I want them to there should be no need for the toggle switch just as Roads88 mentioned Have a great weekend fella's,,,,Larry.