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Discussion Starter · #1 ·
I know this has been an issue with the 6.5 and has been discussed for years.
I have a 1995 C2500 Suburban. New heads were installed about 30,000 mile ago. Had a blown head gasket on the forward right hand cylinder.
Installed new heads and at the same time upgraded the water pump to a HP, new Hummer 10 blade fan and Hayden severe duty clutch and changed from single T-Stat to dual.
I'm the original owner, bought it new. Never really had heating issues until I did these up dates.
So if i'm sitting for a even a short period of time the temp starts to climb and of course going up an incline, same thing. When driving temps stays around 190 or so, as best as I can tell from the factory gauge.
The stack is clean and I even within the last couple of years installed a new Radiator, and not one from the local Auto parts places, a high quality radiator.
I don't drive this Suburban much anymore, Maybe 3,000 miles a year to go from the Dallas area to southern Colorado. Going through New Mexico in the summer can be a little bit of a challenge to keep the temp down, especially with climbing a grade or idling.
Last year I installed another new Hayden clutch, however that didn't help.
Any thoughts or advice?
 

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Never trust a thermostat. The indicated temperature is the full open state. Test it in boiling water using the "curtain area formula" of cylinder head theory. What is this?

Valve lift to diameter ratio yields curtain area, think of the area of a curtain of valve opening..circumference X opening height must equal pi ×radius squared.

With circumference being pi X radius X 2, minimum height is half the radius. Measure the valve opening, the valve must open 1/4 of this diameter.

A thermostat is constantly adjusting its opening to regulate temperature, it doesn't just open or close. As such, it loses coupling fluid through the fit of the piston in the bore. Under this coupling fluid is an elastic diaphragm which keeps coupling fluid from contaminating the wax pellet which is the expansion element. When the wax melts, it expands. This pushes on the diaphragm, pressurized the coupling fluid which then pushes the power piston that opens the valve against the closing spring.

Thermostats are calibrated by selection of wax and piston geometry. The bulb containing the wax can be crimped to decrease volume and open the valve.
 

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I know this has been an issue with the 6.5 and has been discussed for years.
I have a 1995 C2500 Suburban. New heads were installed about 30,000 mile ago. Had a blown head gasket on the forward right hand cylinder.
Installed new heads and at the same time upgraded the water pump to a HP, new Hummer 10 blade fan and Hayden severe duty clutch and changed from single T-Stat to dual.
I'm the original owner, bought it new. Never really had heating issues until I did these up dates.
So if i'm sitting for a even a short period of time the temp starts to climb and of course going up an incline, same thing. When driving temps stays around 190 or so, as best as I can tell from the factory gauge.
The stack is clean and I even within the last couple of years installed a new Radiator, and not one from the local Auto parts places, a high quality radiator.
I don't drive this Suburban much anymore, Maybe 3,000 miles a year to go from the Dallas area to southern Colorado. Going through New Mexico in the summer can be a little bit of a challenge to keep the temp down, especially with climbing a grade or idling.
Last year I installed another new Hayden clutch, however that didn't help.
Any thoughts or advice?
When you installed the dual stat mod did you also install a Bypass Restrictor Fitting ( BRF) onto the water pump crossover to help balance the coolant flows?
 
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Discussion Starter · #6 ·
No I did not installed a BFR. I know Leroy sells them. Lot of opinions about those. I guess it couldn't hurt to installed it.

I guess i could put my old single system back on and see what happens. Again, lots of opinions about how much better the dual is.
Thanks all for your input.
 

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No I did not installed a BFR. I know Leroy sells them. Lot of opinions about those. I guess it couldn't hurt to installed it.

I guess i could put my old single system back on and see what happens. Again, lots of opinions about how much better the dual is.
Thanks all for your input.
Years ago Bill Heath did the research on the cooling issues and found that adding a bypass restrictor fitting helped. Which he added to his cooling upgrade kits.
You can read the review from Bill here:
 

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1984 k10 Burb 4" lift and Hummer 6.5 with a HX35 turbo. 4l80e. Also 2008 Silverado LMM
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My 6.5 turbo was solid until I converted from a v-belt to the factory serpentine drive system. I installed 2200cfm elec fan at same time. Truck would get hot at low speeds and sometimes at higher speeds (ie 75mph). The high output water pump and rear coolant exit mod did not help. I sold it before I was able to try the hummer fan and HD clutch.
 

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Years ago Bill Heath did the research on the cooling issues and found that adding a bypass restrictor fitting helped. Which he added to his cooling upgrade kits.
You can read the review from Bill here:
I have never had an overheat problem with my 1994 6.5 (46,000 miles total), although when I replaced the passenger side head gasket (makes sense now having read the attached) I did replace the thermostat with a cooler opening one from Rock Auto. I have only ever towed a Toyota Yaris (Echo) behind it, so not much weight. The main thing being, we do not get the high summer temperatures in the UK that you get in some of the States. So, even though this has never been a problem for me, the attached was a very interesting and informative read. Background reading & knowledge is the key, should you ever encounter a problem. Once again, thank you for the information Dually & other "informed" contributors.
 
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