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Temperature fluctuations in a 2000 Chevy Blazer

Around January 1, 2010, my car was starting to overheat, and when I brought it in, the shop replaced my radiator (it was rusting from the inside). The car was running great thereafter until the last couple weeks, when I started noticing that the temperature would fluctuate as I was driving.



It typically goes from 190ish to maybe 230, but generally stays between 190 and 210.



Last weekend I took it for a spin, and the temp stayed relatively constant at highway speed, but when I pulled off the highway and into the city, it started to creep up again in slow traffic. I stopped to get a car wash, and as I was waiting in line, it got up toward 230. At that point I put it in park, revved the engine, and it dropped back below 210 fairly quickly with some higher RPMs.



The temp also doesn’t fluctuate all the time, because my girlfriend kept an eye on it for me when she went out shopping, and had no problems.



One thought I had was that the fan motor was going, but other than that, I have nothing. Does anyone have any insight?



Thanks much.

You are right in the range of DexCool damaged vehicles. I submit that a proper flush of the rest of your cooling system was not done and your radiator is clogged, but I would make absolutely sure this is not a simple "need to bleed’ situation.

Do you see any streaking on the hub of the fan (indicating its viscous fluid is leaking), I am going out on the limb here as I only just think this is viscous coupled. Is there resistance to turning the fan after engine is warm? (you want resistance)

Do you know what I mean when I speak of “DexCool damaged”?

Old school - Thanks for the help. I checked out the DexCool stuff, and the Blazer is in the group. I went out and looked at the car, and there wasn’t any streaking on the fan hub. I did notice, though, that my coolant level was quite low (not sure why I didn’t look earlier). It was still bright green, however, so I think they flushed the system, but that there’s a leak somewhere. Does that sound plausible?

Very possible, check around the sealing edges of the intake manifold.

In my experience the 4.3 was not the worst in regards to how many ended up with intake leaks, it was the 3.4 (used in the Venture van) that was really bad, but even the 5.7’s could leak coolant, into the engine, and out on to the ground.