There have been two threads recently on modifying the stock thermostat (a modification that isn’t discussed much anymore) and I recently got to check the new thermostat I just bought out of the box and then with a few different thickness shims. My goal is not to get a real cold thermostat, but rather get one to open around 180 degrees with good flow by the time the thermostat is in the low to mid-190’s. I am hoping that with the DeWitts radiator I have on order and this slight modification to the thermostat, I will be able to keep the engine temperature in a narrow range from 185 – 195 degrees from spring right through fall while ensuring my oil temps are over 200. That’s the goal; guess we’ll see how things work out in the coming months and if the oil doesn’t heat up enough I will re-install the stock unit. The other thing worth noting, the temperatures I am trying to achieve are based on how I typically drive the car as I don’t race the car so extended high RPM runs are simply not in the cards.

In the first photo the thermostat has been disassembled. You can see one of the shims that I made and the hole into which it is installed. The thickness of the shim will alter the opening point by lowering it, or as is the case if you get to approximately 0.100” thick shim, the thermostat will barely close.



One of the problems I ran into was how to measure data so it wasn’t subjective and I could repeat the test fairly well between the different shims and get a good comparison. After some messing around with the test, I decided to take the temperature at three points in the opening sequence. First, by hanging the thermostat such that the neck was downward, it was easy to trap air behind the rubber door that opens in the thermostat. The first data point would then be when the thermostat opened enough to release the trapped air. This doesn’t take much movement at all and you can barely see the rubber door move at all when this occurs since the movement is so slight. The second point of measurement would be when the rubber lip on the seal was even with the flat mounting surface of the thermostat (see the photo). Finally, I took a third measurement when the rubber lip was 0.2” from the same flat mounting surface. While this seems to be a precise number, it is actually the width of my flat screwdriver that I could hold in the water and use for a measuring tool. With one edge of the screwdriver against the flat mounting surface of the thermostat, when the lip was even with the other edge of the screwdriver blade that is when I wrote down the temperature.

Below is a photo of the shim installed prior to re-assembly of the thermostat.



Next was the method of heating up the thermostat so it was immersed in water. In the next photo you can see I bent up a coat hanger and hung it from a small stick across a large pot of water (my wife thinks I should be committed at this point ). The wire next to the thermostat is the thermocouple that was tied into a Fluke Meter for measuring the temperature.



Below is the Fluke Meter that was used to monitor the temperature, which is accurate to 1/10th of a degree.




Here is the data that I obtained, noting each shim was tested several times to obtain these average values:




It appears that with the 0.098” shim, the thermostat is barely closed. The 0.058” shim didn’t quite get me to where I wanted to be. The performance of the 0.075” shim, which seems to seal the thermostat better when it closes down again, will hopefully provide me the temperatures I am trying to achieve in the motor. However, if it is too cool the data will be used to make adjustments as necessary to get to my final goals.

So for now, when the motor is re-assembled in the spring, the 0.075” shim will be the first candidate and hopefully the last.

 

Great post! Thanks for taking the time to get some accurate data, pics and a good write up. I have a spare stock thermostat that I was thinking of modifying and this is the perfect way to get started.

Keep us posted on its performance this summer.

 

Will do. The key will be to keep the oil temp up above 200 degrees.

 

Awesome information Bob, I'm still stuck looking at water pumps and haven't considered the thermostat yet. This will save me some time! Did you go with the Evans pump?

 

good info. takes the 'guess work' out of the equasion.

 

No, I spent the money on a DeWitts instead. I thought that I could better hold consistent temperatures with the radiator and a slight tweak to the thermostat. When my stock pump goes, the Evans or Edelbrock will go in as a replacement.

 

So the ultimate goal is to make the engine run between 185 to 190 regardless of ambient temp? You have collected some data on how the shim affects the thermostat opening, but what is really important is how it affects flow..right? It is possible to calculate (depending on how ambitious you are) how this difference affects the flow allowed. In any case, this mechanical function is only one variable; however, the desired temperature will largely be dependent on the cooling fan settings. How do you plan on correlating the data you have captured with the cooling fans settings? I'm assuming you are trying to achieve an oil temp above 200 F to rid the oil of possible condensation, if so, wouldn't the desired oil temp be above 212 F?

Nice that you are posting your experiment, and sorry for all the questions, but I'm just trying to figure out why you are trying to achieve such a narrow window of temperature operation.

Thanks,

 

On the 2004 & up style thermostat, installing a .150 spacer will keep the ECT at ~172*F-174*F at highway speeds. Then set the fan temps to suit.

Russ Kemp

 

Bob,
Did you look at the Evans thermostat? Do you know what they do to increase the flow through it versus a stock unit?

Russ K,
Good information, under hard driving conditions what does this do to coolant temp?

 

Yes, I spoke to Evans on this but they wouldn't guarantee it would flow more than stock in the stock pump so I elected to just buy a stock unit and try that first. Total investment so far is about $35 including shipping.

 

This is the first step in the process. I know how the car runs now with the stock thermostat with regards to temps when cruising, etc. Obtaining a slightly lower opening will allow me to set the fans at around 195 on/190 off and with the De-Witts cooling should occur quickly. From everything I have read here and on oil boards that I belong to, the optimum oil temperature is 200-210 degrees. As far as temperature band, I am trying to reduce the wide swings and also keep the temperature close to where it will be tuned, so keeping the band narrow should ensure that I don't introduce knock retard due to heat on the road that I may not have seen during tuning.

In a nutshell, I am trying to establish a slightly lower floor for temperatures and upgrade my cooling efficiency with the radiator and fan settings that will stop any temperature swings.

 

Where is the oil temp with that coolant temp?

 

Very maticulous, great data and a good looking post.

Thanks

 

The oil temp is ~180*F-190*F.

Russ Kemp

 

I see. Well, provided you drive the car the same all the time i.e. no spirited driving, hard acceleration, etc. I think you can achieve close to what you desire. I guess I've never considered modding the cooling system since I don't auto-x the car, and mine runs around 190 all the time with the current fan settings.
Good luck.

 

Under hard driving, the ECT will rise once the cooling capacity is exceeded. Then a larger rad would be needed.

Russ Kemp

 

A Fantastic Write Up. Now I See Where The Shim Is Supposed To Fit.
My Thought, For What It Is Worth, Is That By Installing The Shim/spacer, You Are Actually Increasing The Water Flow Opening More Than You Are Actually Lowering The Opening Temp. By Doing This, You Are Able To Pump More Water Through The Cooling Radiator And Back Through The Engine.
I Would Love To See A Flow Test To See If That Is Actually The Case, But Logic Tells Me Yes (althought The Wife Often Questions My Logic).

Another Question: Is The Thermostat Housing Aluminum? So By Installing An Aluminum Shim There Is No Galvanic (?) Issues.

Any Comments?

 

Housing is aluminum, although I am unsure of the alloy. The shim I used was 6061. Guess I will see if a galvanic issue comes up but I suspect the Dexcool should protect it.

Temecula? My nephew sells Harley's at the Temecula Harley dealer.

 

Hey vettenuts,

Thanks for sharing your "science project" with us!

Your temperature monitoring gizmo is especially interesting. Is that some sort of 4-20 milliamp thermocouple? And is that Fluke meter designed only for temperature monitoring, or is it multi-purpose?

Also, is one of your goals to make sure the oil temperature is hot enough to "boil-off" any condensation?

Am I asking too many questions? Again, thanks for the thread and please keep us updated with your discoveries.

 

It is a normal Fluke meter with the option of measuring temperature. I was fortunate and borrowed it from work for a few days

I send my oil out to Dyson analysis for review quite frequently. One of the things that I am always cautioned on is to make sure the oil gets over 200 degrees. Not only removal of condensation, but its optimum for minimizing friction as well. There is a lot of good information on oil over on bobistheoilguy.com.

It will be interesting to find out where the motor actually runs temperature wise when I get this installed with my AFR heads. But if I am off, I think I have enough information at this point to alter the thermostat to get where I want to be.