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Discussion Starter · #1 ·
Hey guys,

I have a strange reaction in engine temp I don't understand. Here are the known elements.

Temp gauge is accurate (verified with laser)
Outside temp is 80 degrees.
Have spring in lower rad hose.
13 lb rad cap.
Stock hood baffle is in.
Griffin alu rad for high hp motor.

Here is what's confusing me. I had a 180 thermostat in, and it ran between 200 and 240. To high for me. So I took the therm out and it ran between 140 and 160, real stable.

So I put a 160 therm in figuring it would be stable at 160 but it runs between 180 and 200.

If it runs at 160 with no therm, why 190 ish with a 160 therm. Is it possible to get this to be steady at 180 degrees?

Should I just run it without a therm to keep it at 160 degrees?
 

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Trifive Automotive Electrical Wiring Expert
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You have some bad thermostats. I went through 7 thermostats from all different manufacturers until I found one that holds my temp at 178 steady. I tested so many thermostats in a pan of water on the stove that my wife thought I would soon learn how to boil water. :) 180 degree thermostats from the same manufacturer, didn't open at the same temp either.
Also, make sure you have all the air out of the cooling system after changing thermostats. My Ramjet is bad about trapping air and causing temperature fluctuations until I bleed the air out.
 

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It's a mystery why you have such a big difference between no thermostat and a 160º thermostat. I suspected that your 180º thermostat was defective. The big spread between the 160º and the 180º doesn't seem right either if the 180º thermostat wasn't defective.

Were all these tested on the same day under the same driving conditions?

Things really don't add up.

On the other hand, if your 160º thermostat results are consistent, there's really no reason not to continue with it. 180º-200º is just fine. Though I expect it's going to run cold when the weather is cooler.
 

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Discussion Starter · #4 · (Edited)
yup, all testing on same day, same outside temp. It's funny, I bought the 160 therm at NAPA thinking that the quality would be better than Autozone 180 I had.

One other thing. Would drilling holes in therm, or just running restriction washers be a solution.
 

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yup, all testing on same day, same outside temp. It's funny, I bought the 160 therm at NAPA thinking that the quality would be better than Autozone 180 I had.

One other thing. Would drilling holes in therm, or just running restriction washers be a solution.
The HP thermostats you can find at Summit and Jegs come predirilled to allow some flow and avoid trapped air. Another possibility to check is your timing: retarded timing or lack of vacuum advance at low rpm can rapidly boost engine temps. On mine, vacuum advance is locked out, initial is 18 degrees with a total of 38 degrees. Consequently it will tend to run hot at idle and the low rpm levels of congested traffic.

My key over the years has been the loss of coolant. Oil temperature is the final arbiter. If the radiator doesn't boil over and lose coolant, the engine will not suffer as long as the oil temp stays under 230. Additionally, I use the rear boss in the passenger side cylinder head to locate the temperature sensor. Head temps are more reliable than intake manifold temps.

paul
 

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Discussion Starter · #7 ·
Thanks, my MSD ign also has the vacuum locked out. My coolant temp sensor is on the head also. I don't know where my timing is set at and I guess I never asked the shop who built the motor.

It's kinda like the motor likes more coolant volume flow. I did look in the radiator and saw what I thought was good turbulence in the top tank.
 

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A little OT but I was told that it is really hard to get a working thermostat first up. The parts counter man told me the reason was that every time a customer returned a T'stat that was faulty, it was put back onto the shelf again, so the content of faulty T'stats rose as a %. For that reason, I closely examine the packaging to ensure it has not been opened and resealed before.
Regarding the cooling issue, have you considered air pockets as a problem?
I had a similar problem, but on a stock 283, then was told that the only way to ensure that air pockets did not exist, was to fill the engine with the top hose neck unbolted (twist it around so it's pointing up) filling using the T'stat housing (T'stat removed) until the water appears at the T'stat housing, refit T'stat and top hose neck and continue the fill using the radiator. This way you can avoid air pockets. This method solved my problem.
 

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My personal opinion is that there aren't THAT many defective thermostats.
And while I'm sure that some returned ones get put back on the shelf, I doubt that many get returned, and many if put back on the shelf are going to show that they are used.

About the only way to determine that a thermostat is defective but not simply stuck closed is to put a suspect one in a pan of water on the stove and bring the water to a boil. A good thermostat will open to about 75 degrees if it's a blade style - I've seen a defective one open only about 30 degrees. Or if it has a vertical movement, it needs to move more than 1/2".

On the timing, retarded timing will produce a lot of heat in the coolant. No vacuum advance is a big part of that. That's one reason you need it. You will also see part throttle performance gains once you fix the timing if it's off.

Thing is though, timing problems causing temperature rise in the coolant don't go along with the wild variations between the thermostats.
 

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ONLY "STANT" thermostats here. never a problem, since i`m 15.
In NZ we cant get Stant commonly, only a brand called Tridon which unfortunately is packed in clear plastic moulded sheet which can be restapled, so that's why the faulty T'stats perpetuate when returned for replacement or credit.
 

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either you run a restriction disk,drilled or a balanced t-stat
my thought is with no t-stat your flowing enough water . a t stat is a restricting flow to much . to test theory drill two holes in plate of the 160 .and see if max. temp drops .you will get a longer warm up but not as slow as open.
also do you know what the water pump flow rate is. ....race belt driven pump are cut back to not loose horsepower at rpm but barely flow enough at idle.
a good pump has a plate on the back of impellers to increase low/mid speed flow
 

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Ok, a 2013 thread revived......But while we are all reading, most modern thermostats have either a bleed hole with a jiggle pin in it, or an air bleed notch on the valve plate. If you are overheating and then fine after drilling holes in your thermostat, you probably filled the system up wrong, trapping as bunch of air. I always filled with the top heater hose off until coolant got there, then closed it up for the final little bit. You can't just fill from the radiator (meaning the system from the bottom) and expect all that expelled air to make it past that little hole in a thermostat. There are some high flow water pumps that might need more flow than a standard stat, but they have high flow stats for that situation.
 
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