Caprice overheat...ahhrrgg!

[royal0014]

I'll try to make this short: 1991 Chevy Caprice, 5.7l V8 (ex cop car). 252k on the clock.

'Couple weeks ago the car ran hot on the wife one morning. No big deal, put in a new t-stat and all was good, she says. This past Monday I needed the car to go to work. 100 mile round trip, no problem. Did notice that the temp was running cool, just barely above 100?.

Tuesday afternoon, I had to go get the wife from Tennesee (VERY long story that I could post in SHT :facepalm. About 400 miles round trip, again, no problems, temp stayed just above 100?. Go to work Wed. night, back home Thurs. morning (another 100 miles). Get about 10 miles from home when I notice the car running hot, near redline. Gauge maxes at 260, so I'm quessing 240-250. Turn on the heater, and it blows cold air, so I know the t-stat stuck closed. Pull over, wait about 20 min. for it to cool off. Pull the t-stat out, pour about a half-gallon of water down the hole, and drive on home. Temp is ok.

Later in the morning, I drive the car to town for another 'stat. Take the 'stat and reciept in to the parts house (Advance). I exchange it and upgrade to what the countergirl said was their 'super-stat'. If it fails, it is supposed to stick open, not closed.

Ok, how do they engineer a stat to fail a particular way

Get home, put new 'super-stat' in car. Doesn't need water, block is full at stat housing, radiator is full. Later I go to pick up my son. Go about 5 miles at 50mph or less, and I watch the temp steadily rise. When it gets too hot, I pull over. Turn on the heater again, only this time it's blowing HOT air. So the stat should have been open, right? About the time I stop, the temp starts to drop. Gets to about 220?, which is mid-scale on guage.

Well, I chance it and continue on to get my son. Temp stays just below 220? there and back, about 15 miles.

So what the heck happened to make it run hot with the new stat open? Have not touched it since I got back home with it. I'll get out there in a little bit and make sure the radiator is full, burp it.

Sorry for the long post. Thanks in advance. Sure someone here will have some Pearls of Wisdom


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[wifisher]

Re: Caprice overheat...ahhrrgg!

Originally the car is running cool. This IS a problem. Usually it is a tstat stuck open. This will cause long term damage if it is not corrected.
When motor is hot heater will work regardless of tstat. Coolant flows through the heater core with tstat open or closed. Did you check coolant level at this point? Usually no heat is from low coolant. This would also explain the overheat. Could have had an air bubble in it. When you open a cooling system, always run the car until the tstat opens, and check level in radiator. Not the overflow. Do this before driving.
220 is a little too hot. Did you verify this temp at the motor. Your gauge may be off a little. Use a non-contact thermometer and check temp at tstat housing. Should be near tstat rating. If the motor is running this hot, I would suspect a dirty radiator. Be sure that the radiator is clean on the outside and air can flow through it properly. Fins are straight, not full of bugs etc. If clean then it will need a flush to remove scale and crud from inside. There are kits available to do this at home, or any repair shop can do it. This will probably fix your overheat issue.

 

[MTboatguy]

Re: Caprice overheat...ahhrrgg!

Sounds like your radiator needs to be serviced, take it to a shop that specializes in cleaning and rotting radiators, the older they get the more plugged they get and cooling efficiency goes down resulting in less water flow through the cores in the rad.

 

[royal0014]

Re: Caprice overheat...ahhrrgg!

Hey guys, thanks for the replies

Checked the level in the rad., a little low, but visable. Puke tank was empty. Cranked up and let it idle until stat opened. Topped off rad, which did not take much, and filled puke tank to 'hot' level.

Drove it to town. Temp stayed between 160-190, even in traffic.

Letting it cool off now and I'll check all again. Hopefully it just had a bubble yesterday.

Thanks again


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[j_martin]

Re: Caprice overheat...ahhrrgg!

Like they say, the t-stat wasn't the problem, except the first cheap stat you put in opened too early.

Cooling system failure of some kind, It's time to check the radiator for blockage, an exhaust gas test (at the radiator, there isn't supposed to be any.) Could be anything. Somehow the coolant is getting overheated and dumped out, or more likely dumped out, then overheating.

One I chased like this for almost 2 years turned out to be a heater hose intermittent leak in an out of the way place. Would run fine for months, then suddenly dump coolant and overheat. Honest, the only fault was that durned hose.

 

[jeeperman]

Re: Caprice overheat...ahhrrgg!

when cold open the petcock drain at bottom of rad.
My bet is you will get only drops or dribbles even if rad is full.
Run a wire into the petcock if possible to break thru the sludge.
Might not get any more rad water because the lower tubes and side tanks of rad are full of sludge.
It could be so bad that half of the tubes are sludged up and only the side tank with the lower hose is still open.

Then if your low on water, it is worse than being that low with a clean rad.

 

[wifisher]

Re: Caprice overheat...ahhrrgg!

when cold open the petcock drain at bottom of rad.
My bet is you will get only drops or dribbles even if rad is full.
Run a wire into the petcock if possible to break thru the sludge.
Might not get any more rad water because the lower tubes and side tanks of rad are full of sludge.
It could be so bad that half of the tubes are sludged up and only the side tank with the lower hose is still open.

Then if your low on water, it is worse than being that low with a clean rad.

I won't even bother with those drains. They clog up way too easy. They are also known to break off when you try to open tham and create more of a headache. If you want nothing more than draining the system, use the lower rad hose. If you think it is dirty, just flush it.

 

[Bob_VT]

Re: Caprice overheat...ahhrrgg!

OLD School...... Have you checked the hoses? Is a hose worn to the point where it can collapse when hot?

 

[bigdee]

Re: Caprice overheat...ahhrrgg!

OLD School...... Have you checked the hoses? Is a hose worn to the point where it can collapse when hot?

I like old school....I am an "OLD SCHOOL" guy too and Bob_VT makes a good point. I have seen people replace the bottom radiator hose with an upper radiator hose...the difference is the lower one is stiff and usually has a coil of stiff wire inside that keeps it from collapsing.

 

[royal0014]

Re: Caprice overheat...ahhrrgg!

Yep, old school is simple. Had not thought of a hose collapsing. I'll have to check that.

Drove to work last night and back this morning, no problems. Temp stayed right at 160?.

Problem may be an occasional coolant dump like JM said, or maybe just a bubble in the system. Time will tell

Thanks all for the replies....


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[Hiya Bayaya]

Re: Caprice overheat...ahhrrgg!

Had similar problem I had an air bubble in the system, ran the car with the rad cap off for approx. 1 hour to let the fluid circulate well and heard a burp come out and fluid circulating, at that point capped the rad and filled the reservoir bottle. No problem after that.
Good luck

 

[jeremy_nash]

Re: Caprice overheat...ahhrrgg!

I had a similar problem with my old 89 caprice. my issue ended up being the fan clutch was bad. I used a few strips of metal, drilled a hole in the strip for the bolt on the clutch, and welded them to the shaft. spaced evenly apart and never had another issue.

 

[fat fanny]

Re: Caprice overheat...ahhrrgg!

Check to see if your system has a bleader valve if it has one it should be located in one of the steel crossover lines in high point of the system. As said the air in the system can stay there for some time and it needs to be blead out burping the cap to get the air out works but can take forever the system needs to be closed to maintain it;s operating pressure.

 

[Lion hunter]

Re: Caprice overheat...ahhrrgg!

I would definately check into having the radiator cleaned. At 252K it probably needs it and if your car uses the radiator to cool the tranny everytime it gets hot it is hard on the tranny.