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Discussion Starter #1
91 4.3l tbi vin Z. I am replacing the thermostat. Should I use rtv/silicone? Or install it dry?
 

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ACDELCO 10105135 GM Original Equipment $1.28 @RA

Fel-Pro makes a fancy one with a rubber O-ring molded in for 5x the price. $7.71 RA
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Discussion Starter #5 (Edited)
Napa sold me a rubber ring that fits around the outside edge of the thermostat. I was told that is all I need. Then I watched several youtube videos replacing thermostat on vin z and everyone says you only need the rubber ring and nothing else. What do you think? To make things more confusing, my Chilton manual says no rubber ring or paper gasket, but to use a 1/8" bead of RTV on the water outlet housing thermistat seat. Obviously when I take off the housing it will be clear to me whether or not there is a flat paper gasket there or if it is metal on metal with just the rubber ring.
 

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That's the only way to find out. Please let us know. I for one thought all TBI engines used the paper.
Do yourself a favor and throw that usually incorrect Chilton manual in your fireplace. They are worse than inadequate, which they are, but also have many errors in them.
 

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Discussion Starter #7


I am not sure what I will find when I remove the water outlet housing. To be prepared, I got supplies for all 3 options. I got the water outlet fiber gasket. I got the gasket maker. I also got a Napa Auto rubber o-ring and I got an Orielly Auto rubber o-ring. Orielly did not have the 4.3tbi o-ring in stock, so I purchased the 5.7tbi o-ring. You can see the difference between the 2 different o-rings in the picture. I will make an update after the repair and inform everyone as to what exactly I found. Shocking that I was not able to learn more about this repair on this forum.
 

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Curious as to how much help you expected for a job the requires taking out 2 bolts, cleaning the surfaces, and reinstalling 2 bolts?
To help you out I photgraphed the complete step by step procedure from one of my old GM S10 service manuals. Since they are very thorough it's an 11 step procedure. 12 if you include making sure there are no leaks since that step isn't numbered. If you right click on the pics you can open them in a new window much larger.

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94 4x4,01 Blazer
2001 Blazer 4dr 4wd LT
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to make life even easier- remover radiator cap (for pressure relief- and drain a bit of fluid out the drain petcock to lower your level at thermostat- less leakage on the block.
 

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Discussion Starter #10
Thanks slayer. Those are the same instructions as the Chiltons manual. I will report back.
 

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Discussion Starter #11 (Edited)
It was a flat fiber gasket. I used felpro. It took 2 hot-cold cycles to get the 2 bolts tightened down. I did not use any RTV. When I first started it and got it up to temp, it seeped a little coolant. Then I tightened up the bolts. Then I let it cool down and then I got it back up to temp and tightened the bolts again. No leaks after that.
 

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Glad to hear you got er done.
Glad to hear Chilton got one right.
 

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Discussion Starter #13
Going to post these pictures incase it helps someone in the future.

1991 4.3z tbi 5speed 4x4 144k miles

I pulled the radiator cap off and pulled the drain plug and let out 1 gallon of coolant.

I disconnected the upper radiator hose from the thermostat housing.

The old thermostat was rusted pretty good. I believe I needed a 14mm socket. A deep well 14mm socket will make things easy but I was able to get the job done without it.



I filed and sanded the housing and manifold. I kept the old thermostat in the housing to prevent anything from falling into the manifold while I sanded.


I installed the new thermostat with no RTV or rubber o-ring.


I installed the felpro fiber gasket dry with no RTV.


I installed everything in reverse of disassembly and tightened it up by feel with no torque wrench.

I added coolant and kept the radiator cap off and started the truck. After about 20 minutes of idle, the new thermostat opened and burped out the air bubbles. I added more coolant and I put the radiator cap back on. I found a small leak and tightened the housing bolts.

I turned off the engine and let it cool. Then I turned it back on and let it idle again until the thermostat opened. I found another tiny leak. I tightened the bolts more. Then I repeated 1 more time cooling down and warming up and tightening the two housing bolts until there were no more leaks.
 
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