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Discussion Starter #1
I just bought a 2000 gmc savanna with 100000 miles. Doesn't overheat at idle or running @ 70. But when I take off from a stop the temp gauge goes up really fast and then comes down real fast. I took the muffler off to help with exhaust gasses, still has the converter. 4 inch pipe not here yet. I'm guessing maybe one of the thermostats may be sticking? Anyone else come across this?
 

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I'm not sure if it is correct, but I get a small temperature rise when I accelerate pretty hard on my truck, but it gradually comes down. I'm with lovoltage, check your coolant level. While you're thinking about it, you may also want to check the radiator for gunk, mostly because you are thinking about the cooling system.

By the way, Welcome!
 

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Fan clutch engaging too late is a possibilty. Clutch finally engages and temp drops rapidly. From new the fan clutches were not calibrated correctly. 15 years and 100,000 miles later, it could be missing much of it's fluid.
Removing the muffler won't do much if anything. Removing the "converter" or soot trap may if it is plugged. Some areas require yearly inspections and removing the converter isn't really a option. They can be "gutted" and reinstalled ,to look as though it has a converter.
 

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Discussion Starter #5
I ordered 2 180 degree thermostats and new fan with fan clutch from ssdiesel. I'm going to flush the radiator. Hopefully all this will fix it.
 

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I ordered 2 180 degree thermostats and new fan with fan clutch from ssdiesel. I'm going to flush the radiator. Hopefully all this will fix it.
The 195 (maybe 190) thermostats are the correct ones for these diesels. The lower temp stats will probably only mask the real problem. Check and clean the other stuff as suggested earlier.

The stock fan and clutch are sufficient to cool these engines IF THE FAN CLUTCH IS ENGAGING AT AN APPROPRIATE TEMPERATURE. The fan clutch may just have gunk build up in the bimetal spring or just need adjusting.

I'm afraid you may just be wasting $ until you fix the actual problem.
 

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Do any of the other gauges seem to move? Just wondering if you have a ground problem messing up the readings?

Have a scan tool? If so compare the readings the computer is seeing to see if the temp is actually swinging that fast.
 

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I agree, I wish you would have asked us before you spent money (especially from SS Diesel). Contrary to popular belief, a cooler thermostat is NOT always a good solution especially in these diesels. The stock cooling system is just fine when it's in proper working order. Stock Delco thermostats and a functional fan clutch goes a long way, as well as a clean radiator. I almost bet your only problem was cheap parts store thermostats. My truck did the same thing when I had a Stant thermostat. I tried two of them and finally bought an AC Delco and never had another issue again.
 

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Discussion Starter #9
Well after messing with it today and reading other posts, I'm pretty sure it has at least a blown head gasket. The top radiator hose is hard. If I take off the radiator cap to relieve the pressure and put it back on and start it. The top hose is soft and I can get heat in the cab as it starts to warm up. As it warms up the heat gets cooler and the top hose gets harder. Which sucks because I just bought it. I dove it home 2 hours @ 65 down the interstate without a problem and the temperature was fine.
 

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Its normal for the hose to get hard after getting to full temp. Its also normal for a rig this age to have a somewhat plugged up heater core, I have one that acts as you describe. It was better after a flush but went back to its old ways the next winter.

What is not normal is if its cold and the hoses are soft, you start it and the hoses get hard well before it gets to full temp. Thats a sign of a head gasket as well as the lack of heat. Lack of heat could be air bubbles not letting coolant circulate or stop leak someone dumped in to mask the head gasket issue plugging the heater core. Stop leak will usually be somewhat visible around the pressure cap and neck area. It kinda looks like a brown slime in those areas.
 

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Its normal for the hose to get hard after getting to full temp. Its also normal for a rig this age to have a somewhat plugged up heater core, I have one that acts as you describe. It was better after a flush but went back to its old ways the next winter.



What is not normal is if its cold and the hoses are soft, you start it and the hoses get hard well before it gets to full temp. Thats a sign of a head gasket as well as the lack of heat. Lack of heat could be air bubbles not letting coolant circulate or stop leak someone dumped in to mask the head gasket issue plugging the heater core. Stop leak will usually be somewhat visible around the pressure cap and neck area. It kinda looks like a brown slime in those areas.




^^^This
 

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Discussion Starter #12
Well decided to change the thermostats any way to see if that would help after the flush. Whoever decided to put that motor in a van should be shot! It'll be a couple of days before I can get enough time to put it back together.
 

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Be sure to bleed the cooling system after you put in the thermostats. The bleeder screw is on top of the stat housing. An air bubble in the system will cause exactly the problems you are having. To bleed. Start up engine get it to op temp. Turn heater to warmest setting. The open bleeder till all the air comes out.
 

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So here's where I'm at. I replaced both thermostats with 180 degree. I replaced the fan clutch because it was weak and new radiator cap. The first time I started it I bled the sys. and the temp still crept up slowly while idling so I cut it off thinking head gasket. So I got a block tester to see what would happen. I started it with cap off but the water would come out until the thermostats opened. I put the cap back until around 180. It released pressure but stayed at 180. I put the block tester on and it would start bubbling by itself. I left it on for 3 or 4 minutes and the liquid stayed blue. I done this 3 times so I'm thinking maybe head gasket not blown? I put the cap back on and let it idle for another 10 minutes or so and the temp stayed around 180. I let it cool down to hook everything up to take it on a test ride. After doing all that I top it off and start it up. I crack the bleeder just to make sure no air. The temp trys to creep up so I take the cap off. It cools back to 180. I top it off and put the cap back on and let it idle for a few minutes, still 180. I take it down the road at 60 come to a stop and turn around still 180. Head back and come to a stop. After I turn on my street It starts to heat up. Pull in my drive way and try to take off the cap. After getting it off and hot water coming out the temp goes back down to 180. So now what?
 

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I started it kinda cold again. There was still some pressure on the top hose. It crept up to almost 210 so I to the cap off and it went back down to 180. I top it off again bled the sys. and put the cap back on. It idled for about 40 min at 180. I hit the bleeder screw a couple more times. Went down the road again. When I came to a complete stop it was @180. When I took off again it went up to 210 fast turned in my driveway and went down to about 200 and stayed there. When the gauge is at 180 the heat works. When the gauge goes up the heat blows cold. Is there still air in the sys. causing all this?
 

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Have you read Post #8?
 

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So why does it stay at 180 with the radiator cap off? Riddle me that batman
It is not just about 180F t-stat.

Are SSD t-stat ACDelco? Not sure, if they do, then you are fine.
A lot of aftermarket t-stat are not good.

The 180F t-stat will not solve any temp spike issue, either.
I know it is not logical but this diesel actually needs heat.
Have you checked the temp sender, and if you replace sender, make sure they are ACDelco also.
 
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