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1995 GMC 6.5 TD thermostat

S

Steak&Eggs

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Location
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I noticed the engine temp running high than normal and thought I would get a new thermostat. I guess it came with a 195 degree from the factory, I thought I would get a 180 degree and see how that worked.

I checked the local parts stores and only found stock replacement and $30 cost - I thought that a little steep so I found this on ebay (supposedly Higher flow) High Performance MotoRad 2065 180 Thermostat for Chevy GMC - they do not list any engines, only year and make and those start at 96... (mine is 95) carid has what looks to be the same unit but they only show their part number not the motorad number. So cant seem to cross the numbers.
Its on ebay here: https://www.ebay.com/itm/2863209322...dUXyB3pNm25+eoXo2Y0oEN8N--U=|tkp:BFBMytHarphm

I will take out the original and see if it looks the same.....

What is the thinking on replacing the 195 degree unit that has been in the engine since it was new with a lower temp 180 degree unit? Or should I stick with the higher temp? It never has ran over temp previous to this...

Thanks, Larry
 
Could also be the fan clutch not locking in like it did before so many miles.
You can do a test on Your old stats by hanging them on a string in a pot of water.
Heat the water and when the a stat falls from the string read a thermometer thats also hanging in the water.
 
iirc dual stats didn't come out until 97. there is a one of a kind much saut after 96 style, but anything older should have a single stat with a block-off plate like the ones in the link I posted above.
 
While your in there with the thermostat, when was the last time you flushed the cooling system? I mean pulling the block drains, removing the coolant recovery thank and rinsing it out and possibly even going as far as pulling and flushing out the radiator?

I wish I had a video of when I flushed my 95, but I had pulled the recovery tank which is a pressurized type mounted up on the firewall (my radiator does not have it's own cap) I had thought it was clean, but when I pulled it and hosed it out there was a massive amount of mud inside! and I do mean a massive amount... I couldn't get my block drains out due to their location and where the motor mount brackets were on the block, but I flushed everything else out. ran water through everything until it was clean, then still with the garden hose flowing into the top rad hose with no stat installed, started the engine and even more muck came out of the block! it was unreal the amount of crap that was trapped in the block, radiator and recovery tank!

Oh yeah, if you radiator is of the OEM type and still original to the truck having the garbage plastic tanks, be prepared to replace it or have the tank replaced! the hot side (top rad hose side) gets very brittle due to the heat cycles. best thing you can do is get an all aluminum champion radiator. preferably one that is for an older rig that has the radiator cap on the tank. one of these days I will do that on mine, I ended up having the plastic tank replaced on mine because it was cheaper for me at the time.
 
Another tip... do NOT use the GM orange DEXCOOL !!!! go back with the old school green antifreeze, and these diesels do not need any PH modifiers like the newer diesels need. those additives actually do more harm than good on these old IDI engines. the GM dexcool gets very corrosive, I have seen it eat aluminum as well as when it dries on the block from a leak and you use a power washer to get it off, you will see that it has eaten the block paint down to bare cast iron. all of these environmental gurus came up with "friendly" coolants among other things but they all have their cost to the end user... shorter vehicle life...


depending on your budget, and not if but when it happens were you have to replace the water pump, start saving up your loose change for a water pump that was made for the 2000+ model 6.5. these pumps use a spin on type fan clutch, but there are good options available along with using the 2010 model express van duramax fan and electro-viscous fan clutch. @ak diesel driver had a good writeup on this here in the fourm and is well worth the investment especially if you do towing and hauling.

essentially you use the WP from a 2000 truck same engine 6.5l, the plastic fan blade from a 2010 duramax express van along with the electronic fan clutch, a hayden electric fan controller made for dual electric fans, and if you so desire, an led in the cab to see when the fan is on.

the fan controller can be wired up so that when your AC is on, the fan clutch is on too along with an override switch in the cab to manually turn it on if you need it like with towing/hauling on a grade incline.

we can get you the part numbers and it's all a direct bolt on, no modifications needed other than maybe trimming the fan shroud for the electrics on the fan clutch and with this upgrade, you will find out in a hurry if you need new motor mounts, there is maybe a 1/4" of clearance for the fan blade in the shroud!

Note: you can also use a normal fan clutch with this setup as well, we can find the hayden part number for it as well if you don't want to wire in the electric one.


I did this upgrade to my 95 a couple year back and let me tell you when that fan clutch kicks in, there is a tornado under the hood! instant driveway clearing leaf blower LOL
 
@Will L. led me to a test.
It destroys Your fan clutch but is a sure fired way of testing to see if the fan clutch has failed.
He advised me to drill a hole a little smaller than a sheet metal screw through the fan clutch, then install that sheet metal screw through the fan clutch, locking it solid.
Now take it for a drive with the fully engaged fan clutch.
 
Use only ACDELCO, GM or something else that's recommended on this forum.

A lot of people have wasted time and money on aftermarket thermostats.

Check everything before replacing your thermostat.

Has your cooling stack been cleaned lately?

Check your thermostat in a pot of water.
 
A lot of good info ! I needed to be reminded to flush the system - though I probably would have thought of that when I was replacing parts. Since Leroy is a sponsor I think I'll get the thermostat from him. After all it has been a working truck all its life and no issues, so I guess it will work OK. The electric fan mod sounds like a great deal but out of my price range now! I will verify the failure of the thermostat before replacing it!

I was working in Delta Alaska at -60 below and came out one morning to plug in the truck and noticed coolant on the ground under the left side of the radiator... I plugged it in and went back inside for coffee - when I came back out the leak had stopped. It did not leak much - about a cup or so. I guess the plastic and AL do not shrink at the same rate. If I replace the rad it will be all AL! I left the rig plugged in all night after that!

Thanks, Larry
 

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