what should the normal operating temp. for a 1968 400 yt block on a 80degree day be? I'm running about 190 to 200 depending on traffic at speed about 35 to 45mph. I have a 160 degree thermostat in the car right now what is the stock thermostat set at from the factory?
I'll preface this by saying "in my opinion", that running temp is fine, but I'd go with at least a 180 degree stat, not sure what the 400's spec'd out at for the stock application, but I'm running a 195 degree stat in my 350 and rarely see north of 200 degrees.
Engines are designed to run within a certain temp range. Putting in a 160 thermostat logically would just mean that your engine is going to take longer to get to a normal operating temp. A clutch fan puts out a lot more air than a flex fan. Upgrade if you want to run in the 180s. 210 IMO is the edge of safe driveability. 180-200 is fine. I run 185 to 195 normally with my 69 with the stock flex fan. I've got a clutch fan in my 79 TA, and the TA runs at 180 flat with the clutch fan, really hot days it might be at 190.
Putting a 160 thermostat in would NOT make the engine take longer to get to normal operating temp. If you coolins system is up to snuff it would NEVER get there. The purpose of a thermostat is to SET the normal operating temp. If you are running a 160 stat and your car is running 190 to 200 your cooling system is inadequate. A couple degrees above or below the stats rated open point is normal but if you are that much above your stat rating you have cooling system issues.
Tstst only tells the system when to open....down in hot Texas I ran 200-210-up to 220F in the summer for 10 yrs....it would be 180-190 in "winter".... I just replced my radiator to a large 3 core aluminum and it brought my 220F down to 190F at 80-85 mph...in 85-95F weather.
running 190-200 is not too hot....if it stay there... what does it run in same temperatures in idle and in speed? like 80 mph?
That's what I figured. Also, when that stat is opening at 160 degrees, I doubt it will ever shut again during that drive cycle. The system is not letting the coolant stay in the radiator long enough to release the heat(not that you have an overheating problem) I'd go with a new stat, see where you are at and then start looking at other components if you think you have an issue, ie. fan/clutch/radiator/timing. Also, did you put that 160 in, or did you get the car with it?
That's what I figured. Also, when that stat is opening at 160 degrees, I doubt it will ever shut again during that drive cycle. The system is not letting the coolant stay in the radiator long enough to release the heat(not that you have an overheating problem) I'd go with a new stat, see where you are at and then start looking at other components if you think you have an issue, ie. fan/clutch/radiator/timing. Also, did you put that 160 in, or did you get the car with it?
exactly! that Tstat doesnt make water colder...it just releases the water at a set temperature...it doesnt mean it stays that temp.....some people take e Tstat out thinking it will cool better...it runs too fast then...if you take a Tstat out install a washer with a hole about the size of open Tstat so it slows down, have time to cool...
I was under the impression that the main purpose of any cooling system thermostat was to allow the engine to reach operating temperature ASAP. Good for the motor to run properly plus allowing interior heat ASAP.
Another function is to keep the radiator out of the loop during cold winter conditions, which is also trying to maintain a proper engine operating temp.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
This is from a burned out memory, lol. Got my 1st car(68FB 350 HO - w/o gauges) back in 75. Had a factory clutch fan with shroud. Stock radiator. No baffles in front or top. Drove-n-street raced it all summer no overheat prob. Installed a 70 RAIII engine w/a TH350 trans next spring. Drove-n-raced all spring no prob. But noticed it was so hot under the hood with both engines. Installed a set of aftermarket gauges in July. It was run'n 210. So of course i put in a 180. Then it was about 195. So...put in a 170. Now it was about 185. It felt like it was slower, so my buddy run me in his 68 Roadrunner. We tested each other whenever one changed som'tn. Sure enough, it had. So put the 180 back in and ran him again. It was back. From then on i found all my HP Pontiac street engines like about 190 "at the line" best.
The purpose of the thermostat is to keep the engine temp where the engineers believe it performs the best. Yes it does help it warm up faster than no thermostat but it also allows the coolant to flow at a slower rate through the radiator. If your cooling system is up to snuff your engine should never run above the stats temp rating. What I am trying to say is changing to a higher temp stat is NOT going to solve your issue. Look at all the things in the previous posts to resolve your problem. I put a 180 failsafe in my new engine last night.
Ok, i'll make a correction. Not that i doult it. From 72(oldest GM Pontiac catalog i have), GM only sold 195* replacement stat's for all 66 and up Pontiac V8's. Now i'm gon'a have to dig around and find some i've had since the 60's. Ya, i'm a "reforming" hoarder, lol.
You might want to test the thermostat. Rumor is that some of them are not opening at the rated temperature (probably because they're sourced offshore and not properly tested before shipping).
Also, there are also a couple different types of thermostats, here's a good thread:
