View Full Version : Opnions Please - 180 vs 190 degree thermostat

SC Spyder
04-10-2009, 08:23 AM
In the interest in improving fuel millage I am considering exchanging my 180 degree thermostat for a 190 and the O2 sensors.

To date, the best (average) millage I've seen is about 28 mpg and I see where some of your (much heavier vs my 2700 lb) cars are delivering that and better so I am wondering, if replacing the O2 sensors and or the thermostat will improve that.

If you don't mind I'd like to here your opinions.


04-10-2009, 08:47 AM
I'm running my car with a 180 which I've tuned it for and she gets 30+ mpg. My car typically runs around 188 for normal cruising etc, and when I race it, it'll get to about 194 which is the highest I've seen it. Thats with a stock rad and the a/c condensor installed and properly running fan. I actually have to alter the tune to exercise the high speed mode of my fan because it doesn't come on with normal driving ;).

The stock tune your running is geared for the 195 tstat, and unfortunately the fans are setup to not come until 220 and 228 which is too high.

If your not going to get a chip, then stay with the 195. If you go to a 180 without getting your tune adjusted, then the car's mileage could suffer and you'll increase the risk of over heating.

In my opinion, a 180 is better for our cars as that is less wear and tear on the motor because of heat.

Unless the O2 sensors are fouled up, they should last for quite a long time with no noticable degradation. Things that will foul them is coolant leaks, running rich or lean, overheating conditions, running leaded fuel and age (what doesn't age affect :rolleyes:).

ps in all this speal, to sum it up, get a tune :).

SC Spyder
04-10-2009, 09:20 AM
ftuner - Please correct me if I am wrong ... the cost of installing a chip is not only the chip but because it does not compe programmed for the vehicle or have any info on it and must be programed buy the installer and that should obviously be done with a Dyno tune.

Do any of the chips available have a base program (is this refereed to as a MAP?) already on the chip so a person could install it then at another time have it "Dyno tuned".

04-10-2009, 09:41 AM
Initially you can get a base tune for your setup without the need of a dyno etc. Since your setup is close to stock so to speak, then its more just optimizing the existing stuff thats in it, and changes to the fan on temps etc can be made.

So your paying for the chip and a base tune. Either myself or Dave Dalke can supply you with this. Later when your ready, you go to the dyno and gets things really dialed in.


04-10-2009, 12:56 PM
>In the interest in improving fuel millage I am considering exchanging my 180 degree thermostat for a 190...

I would try that...maybe, if nothing else, just as an exercise to gather data - and maybe higher, to the stock SC stat (192~197?). Problems associated with running too cool include low mpg., rough idle, hesitation and stalling.

I would consider 28 mpg. to be a decent target for the Spyder and change stats primarily to deal with issues that may be generally related to running below optimum temps.

Have you ever run it with a higher stat? How old is the ECT? Sorry if I missed it...was the block fresh or used?

What type fuels are they selling there now? Do they sell one type specifically for winter months and another for summer (doubt it). We're just switching over out here.

XR7 Dave
04-10-2009, 02:00 PM
Gear ratio is the biggest factor that affects mileage. Running the motor at high vacuum due to the light weight of the vehicle greatly increases pumping losses during cruise minimizing fuel economy gains due to light weight.

If you could lower highway cruise rpm to about 1500 mileage would increase significantly.

SC Spyder
04-11-2009, 10:09 AM
KMT - the engine is fresh 2 - 3 k miles (stock 93 with a 0.030 over bore), 2 1/4" true dual exhaust with 2 1/4 crossover, high flow Cats & 3 chamber Dynomax mufflers. On the intake side, K & N on a 15" long stock dia intake, 5% overdrive Jack shaft pulley and A/C & Power steering delete.

The (ECT) Engine Coolant Temperature sensor is new (3k miles), I run 93 Octane fuel and injector cleaner every 3 - 4 tanks, not sure if/when they switch blends down here.

I have not tried a different temp thermostat yet. When I put the motor together 18 months ago, I had intended to chip and dyno tune immediately but I have been self employed (some call it unemployed, I prefer to refer to myself as a consultant or in some cases ... contract labor) for over a year so that has had to take a back seat for now.

Dave - I am currently running 3:00 - 1 final drive. Around town the transmission up shifts between 45 - 50 and the RPM drops to around 1200 RPM. Out on the highway at cruise (70 - 80, love the Florida highway speed limits) the engine is in that 1500 - 1800 range.

04-11-2009, 11:10 AM
Interesting thread. Not to hyjack this thread, but this thread go me thinking in another direction for Frazier or Dave. If you go to a 180 tstat, chip assumed, would that actually lower the temp at the radiator ? What I'm getting at is to increase the efficiency of the a/c by lowering the evaporator temp, especially in traffic in the hot dallas sun.

XR7 Dave
04-11-2009, 11:29 AM
If you raise your fan on temps to 200 deg will the engine run warmer? That all depends on how good your cooling system is. On my XR7 with a 180 deg thermostat and a Griffen radiator, it rarely gets to 180 deg. Most of the time it runs 160-170deg which is probably too cool for good efficiency. On the other hand my stock XR7 also has a 180 deg thermostat but I set the fans to come on at 200 deg and the car normally runs between 190-200 deg. So whether or not there is something to be gained by changing thermostats is a function of how warm the motor actually runs. With a 180 deg thermostat you should run 190 deg min most of the time. If your car runs at or below thermostat temp, then I'd raise the temp to 192, but no higher. With a 192 thermostat set the fans to 200 deg.

SC Spyder
04-11-2009, 12:32 PM

I am running a 1966 Mustang, 4 core radiator. It was referred to as a Desert Core and it cooled the previous 351 without any problems.

Typically, with an air temp of anything less than high 70's the indicated water temp appears to be 180 ish. While in city traffic, with stop and goes, the temp will climb until the fan comes on 220 ish then drip back. On the highway, there is never a problem. Of course the hotter the air temp, the warmer the motor will run. On cool days, below 70, the indicated temp barely reaches 180. On those times when the motor is cool and I am sitting at a traffic light, I do smell gas.

04-11-2009, 12:56 PM
>engine is fresh 2 - 3 k miles

The engine might not really be broken in yet - in which case I wouldn't look too close at mpg other than as a data point for later use. Same might go for temps, as they can run higher when fresh, but that all depends.

>I have not tried a different temp thermostat yet. When I put the motor together 18 months ago, I had intended to chip and dyno tune immediately.

OK, no problem - t-stats and labor to replace aren't that bad so while you wait for a chip, up the stat.

04-11-2009, 01:40 PM
With a big rad like that (wish we could run that ;) ) you could be running too cool so going up to a 190 or so tstat could be great for you.

Also, I'm not too sure but I think having such a temp change like you have at stop-n-go from 180 to 220 back down again would put more stress on the motor.

From what I've read, and others could correct me, but what we need to do is to try to set the operating temp to be consistent, except of course when things get extreme. Like Dave mentioned, and in the case of my car, she'll stick around 188 on average with a 180 tstat and the low speed fan set to 190.

This is where using the QH in your case would be great because you could log a day of driving and start fine tuning your cooling system with that information ;) so you can reach a "stable" operating temperature for your car.


XR7 Dave
04-11-2009, 02:12 PM
You should not smell gas unless you don't have a purge canister properly connected. Regardless of engine temperature you should not smell gas other than perhaps on a cold start in the morning. The car runs closed loop regardless of engine temperature, so the old idea of a rich mixture when engine temp is below 180 deg went away with the carburetor.

04-11-2009, 04:04 PM
>On those times when the motor is cool and I am sitting at a traffic light, I do smell gas.

Originally Posted by SC Spyder... (http://www.sccoa.com/forums/showpost.php?p=804376&postcount=20)
"565 Canister Purge circuit failure. I don't have the canister any longer!"

SC Spyder
04-12-2009, 12:21 PM
ftuner - The early mustang radiator is almost the exact same size with the exception of the thickness. The lower hose is located on the passenger side so a new lower hose is needed. See the attached photos.

XR7 Dave - The purge canister and associated parts didn't make the cut but maybe I'll revisit that. There might be room under the nose for those parts.

ftuner - I like the sound of the Quarter Horse system, sounds a lot like the Holley Projection system that the Spyder had with the previous engine (351). Nice system and easy to tune.

Gentlemen, thank you all for your thoughts and I think for the short term I will replace the thermostat and look into reinstalling the vapor canister system.

I appreciate your input.