Over heating truck

[the turtle]

Hey guys I got a problem with my 88 Chevy K2500 5.7l truck. I haven't had it a long time, but I've put 3 thermostats in it and I'm still having trouble with it getting hot. So I put a thermostat in it when I got it back towards August, as it was running hot. It was running up around the 210-220 mark. So then it would go up past 220 and then come back down. This continued and got worse as it went. So I got another one and had the same problem, so I was thinking maybe it had an air pocket or something. I pulled it out and drilled a couple of 1/4" holes around the base for it to bleed past. That worked fine, but then it hardly got up to 3/8 on the gauge. With winter coming on, I wanted it to get warmer and warm up quicker. I bought a new thermostat....spend a few dollars more and get a "better one". I put it in yesterday and now I'm back to the same thing. It just buries the gauge fairly quickly.

So I've noted that it's not pushing coolant past the cap, which I would attribute to a head gasket failure. I noted just a little bit ago that the upper hose was really hard, like it was pressurized. Upper hose was not warm or hot to the touch like coolant was flowing through it. I also noted that while it's running and the cap is off, it pushed coolant up out of the radiator and then goes back down, but comes back up again. It's sort of like it's pressurizing inside the system and then it's not and it keeps going through this cycle. I used my tester to see if there was any combustion fumes coming through the coolant and the test fluid did not change colors that I could tell, so I think I'm good there. I'm not 100% sure of this. The other weird thing is if I'm driving down the road and it gets hot, I mean the gauge shows 280 and the check gauge light comes on, so I shut the truck off while coasting (it's a standard tranny). Then I refire it after coasting awhile, the temp has come down, sort of like the thermostat opened up or something and now is letting coolant flow.

I'm really out of ideas for where to go next. If this was the first thermostat, then I'd think it was the thermostat, but I just don't see 3 thermostats doing the same thing. I'm wondering if I should look at the fan clutch or the water pump or something else? Anybody got any ideas or had any experience with this situation? Should I get yet another thermostat and just replace it again to see what happens? I'm contemplating putting back the thermostat that I drilled the holes in so I can drive it more than say 2 or 3 miles before it gets so hot that I worry about it. I'm hoping I don't have a blown head gasket, but I guess it's possible. I'm lost and not sure where to go now. Thanks, Jason

[msims]

you should've shut it off way before 280

[Larry Jr]

see how easy the fan turns by hand, if the fan clutch is weak it will spin fairly easy, a good fan clutch will have resistance. something you might do is buy a new radiator cap. believe it or not a bad cap will have the same issues you are describing

[the turtle]

I figured I'd pick up a new cap and probably a fan clutch. There's some resistance, but lighter than I'd like or feel like there should be. I'm not 100% sure the gauge is right even. I say this because I have an infrared laser thermometer and 220 is as hot as I've found, minus the exhaust manifolds by accident. That was somewhat alarming until I realized where it was hitting. I also am not sure because I pretty much had to drive it half a mile or so the first time it happened and I've found no ill effects from this. Thank you sir for your input. I felt like I should lean that way, but needed/wanted someone to put me over the top for my decision.

[msims]

does it get hot enough it's boiling coolant out or is the gauge wrong ????

[the turtle]

I've found no sign of actually over heating other than the gauge. Its just weird that it pushes coolant out, with the cap off, in spurts. Just pushes it up over the top of radiator, not like way up and out. Also the upper hose being hard/pressurized is weird to me as well.

[zziggy]

Was the water pump changed before you got it? Was a STD rotation pump used by mistake?

Other than changing to a new water pump to be sure and a new radiator plus a 50/50 mix of coolant. The stock t'stat is a really hot one, a 210 or so. For emissions sake.

[the turtle]

Factory thermostat is 190 and that's what in it. I really just can't believe 3 stats would be bad in a row. I'm not saying it's not possible, but unlikely I'd think. I'd had contemplated putting a new pump on as well and probably will anyhow here shortly. I just need it fixed before something big goes wrong due to this problem, especially a freaking $5 part.

[msims]

can be any number of things ,,,wrong rotation on the water pump,,impeller rusted off waterpump ,,,fanbelt slipping ,,,fan clutch bad usally at highway speed u get enough air through the rad to keep cool ,,, if it's not getting hot enough to boil i'd think sending unit bad or temp gauge bad or wrong sending unit to match your instrument cluster ,, could be timing too fast or too slow overworking the motor

[zziggy]

Put an actual thermometer on it.
Or a heat reading gun at the radiator.
A different temp gauge.
A different sender.

[the turtle]

My IR temp gun, which ain't no cheap one, shows 2-210 degrees on the heads. I put a new temp sender in it real quick tonight and thought maybe that would solve the issue, but it doesn't. Gauge still goes up to max at like 280 and the idiot light comes on, however, the temp gun shows about 170 at the stat housing and 180-210 on the heads depending on exactly where you put it. I'm about 100% convinced now that I just need to put a manual gauge on it, figuring there must be something wrong with the factory one in the dash. There's no way it can go that high and not push water out of the overflow tank or at least smell like it's burning up or something and there is absolutely no sign of overheating, except the stupid gauge! I'll go ahead and flush the system, change the water pump, and fan clutch, just because it probably needs it anyhow, but I think I'll have to let it warm up a tad before I do that. It still kills me that I can drive down the road and that thing gets up there, but yet I turn the motor off, coast for 2 or 3 blocks, start it back up and it's dropped from say 250ish to under the 210 mark. I just don't see that happening in real life. There's no way you can lose 40-50 degrees of temp in just a couple blocks of coasting. This was the biggest thing that I felt pointed to a gauge problem.

I mean if I'm wrong, please feel free to comment, but if it was an airflow problem, coasting with no fan running at all wouldn't kill that much in temp, as well as no water circulating in the system. If it was a airflow problem I'd think at freaking 20degrees ambient, such as this morning, it would not gain that much when I'm doing 55mph down the high way! If it was a water flow problem, then shutting down the engine and the water flow would not help the situation at all from my point of view. I also find it hard to believe, based on my original theory of stuck stat, that two 1/4" holes that I drilled in the 2nd stat would make that much difference! None of it makes since, but since I've hit at least 280 degrees by the gauge on multiple occasions, and have no ill effects such as knocking, water in the oil, oil in the water, no odor of burning up, etc, I just can't buy that it's actually over heating, not to mention the dang IR temp guns says otherwise. I just don't see it. Also I've been working on my Google-Foo when I have time with this matter and I've found several people having similar issues and finally putting a manual gauge on it to find that the gauge/sender setup is evidently the problem.

Anyhow, guys thanks for your opinions and feel free to point out anything that I'm overlooking or not seeing clearly! The last thing I want to do is need to replace the dang engine in my truck at this time of year.....or any other time! Now with that said, I wouldn't mind putting in a built engine, but I think my hot rod days are mostly behind me! This old truck wouldn't last long that way I don't think. Thanks, Jason

[the turtle]

Ok just a little follow up on the situation. I replaced the temp sender for the factory gauge and same problem. Put a mechanical gauge on tonight, which I should have just done last night but it was really cold! The mechanical gauge shows that it gets up to maybe 220 and then cycles and goes back down to 180 or so. I was certain that it would be something along those lines after some testing, searching, and my experience with mechanical workings. So I'd say problem fixed and the gauge was the problem the entire time!

FYI I'm still going to flush the system, change the water pump, fan clutch, and radiator cap, as well as the lower hose and heater hoses. I changed the upper when I put the 1st stat in after buying the truck. Anyhow, I'd like to thank you guys for your time and information. Thanks, Jason

[msims]

if it running ok why change stuff,, u must have too much $$

[the turtle]

Negative on too much money. Just figure I could do some preventative maintenance and eliminate the possibility of a failure when it's most inconvenient! Hopefully anyhow. Also I'd be curious what will happen this summer when I get the A.C. up and running again. The good thing is that I can do this stuff when it's convieniate for me.
Thanks Jason

[amcamx]

There is supposed to be a 15 degree difference, between the inlet, and outlet hose, of the radiator.
If it is less than that, the coolent may not be moving, or the outside of the radiator could be dirty, or the radiator could be bad.