1988 Chevy 1/2 ton overheating

[Treal]

I have a 1988 Chevy 1/2 ton pickup with a 350 cid engine automatic transmission that has 70K miles. It overheats at an idle after a long drive because the coolant is pushed up to the reclaimer and the radiator is low. The coolant stays in the overflow even after the engin cools off. I believe the problem started after service on the cooling system, new antifreeze/flush and thermostat replacement. No problems driving local streets 10 to 20 miles but on a trip,every time. The hoses are almost new and I have replaced the cap... any suggestions?

[BOOZER]

If you had no problem prior to the service I'd be double checking that the t-stat was put in correctly, the spring toward the engine & that the system is purged of all air pockets.
Lets start with that, & hope your not seeing small bubbles with it running at the neck.

[Treal]

The thermostat is in correctly and is working. I needed to
add a little coolant after inspecting the t-stat and did notice
a few bubbles at the neck but they stopped when the
radiator was full. What does the bubbles mean?

[BOOZER]

If the bubbling stoped your OK. If it continues you
would probably have a head gasket problem. You would continue to see small bubbles unlike the large
ones you get as you purge the air from it.
Shout back if you still have problems.

[CK4me]

Sorry, this post is a little long.

I just wanted to share my experience to date for the above post.

I'm actually going through the same thing right now on my 1993 4.3L. I'm comparing it to my 1994 5.7L and the cooling system appears to be the same.

I'm new to the board but this is what I noticed with mine:

Around town it's fine but eventually, or on long drives, the coolant bottle level rises over the hot mark and does not return to the radiator after the engine cools. I also notice that the radiator seems to hold pressure "far after" the engine should be cool. (several hours).

Since I have 146K on the odometer on the same water pump and I beleive the same thermostat, I decided to do Pump, new cap, all hoses, thermostat (all bought at dealer) - except the hoses -.

After the parts replacement, Same problem as before - no change. After about 1 - 2 hours after stopping the truck, pressure is still high, coolant is still over the Hot Mark and the top hose is very "hard". Sometimes, you can remove the radiator cap 1st thing in the morning and still have some pressure in the system. I don't notice this on my other truck.

Bad thermostats are sometimes common so I swapped it out. No change.

Unless I have some trapped air in the system. (Beleive me, I really think I have this thing purged. I've never had a problem on the other truck). I really hope this is the case.

I know the coolant is never going to "return from the recovery bottle" while there is 16 psi in the radiator! As the owner of an old Jaguar V-12 and and Oldsmobile 455 (now 468cid), I've had my share of "cooling issues" thats for sure.

Could someone correct me if I'm wrong.....

From what I understand (about some of my newer cars with similar systems): instead of an old system with just an "overflow bottle". The systems that use "recovery bottle" like this one, need the cap on the coolant bottle functioning properly. I'm not sure if this system works the same, but other systems I've seen, "bleed some of the pressure" into the bottle after the engine is stopped. As everything cools, the pressure above the coolant level in the recovery bottle is higher than the pressure in the radiator/engine and helps to "push" the coolant back into the radiator. If the Black cap on the recovery bottle is "inoperable, cracked or leaks, the recovery bottle won't hold pressure and coolant won't "go back into engine". (My other car actually has no radiator cap on the radiator at all, it's on the recovery bottle.)

I'm going to try to a new Recovery bottle cap tomorrow but really don't expect any change so If anyone has any ideas, please let me(Us) know. My next step is to test the coolant for exhaust gasses with the test strips that are available.

I'm also going to do a pressure check and see exactly what it is at the cap. I'd appreciate any advice from anyone who had gone through the same problem. I just wanted to add my current experience with the above post. It's very possible, as the above post said, that a head gasket (or worse) could be the culprit. - I never like when a cooling system holds pressure like this. (although I don't get any visible bubbles in the coolant or bottle while its running.).

[dirt49er]

how long did the small bubbles last for??? and is there white smoke coming out of the exhaust, because you might have a bad head gasket. pull all of the plugs and look at them, if they are a little black on one side, and a little white on the other ur ok, but if one of them, or a couple have a whole bunch of wihite shit on them, then you have a bad head gasket.. another thing that you might check is the hose that runs from the radiator to the coolent overflow jug if it might have something in it. because when there are 15 lbs. on it the water will pass, but when it goes back, it has no force at all.

[dirt49er]

also you can go to the smog check shop and have them take off the radiator cap and place the sniffer above it to tes for hydrocarbons, and thats another sign of a bad headgasket.




and to the guy above, your head gasket is fine if it holds pressure for that long, check the thermo one more time...

[CK4me]

and to the guy above, your head gasket is fine if it holds pressure for that long, check the thermo one more time...

I agree. It's holding pressure throughout the night so I think I'm fine as far as the head gasket goes. I also used the pressure tester that replaces the radiator cap and it holds pressure just fine up to 25 pounds. No white smoke at all from exhaust and plugs are fine. Also,, The test strips indicate no exhaust in the coolant eitherl. Unless 3 thermostats are bad, I can't imagine I still have air in the system. Always something interesting......!

I 'm going to remove the T-stat altogether for a day or so and see if the coolant returns as it should. A Service Bullletin for my 3500 suggests drilling a 1/16" hole in the T-Stat to help the "coolant return". Most systems like this will usually have a small hole or "jiggle pin" in the thermostat. This one does not. I may try a small hole in one of the thermostats as a test. I'll remove it first and see.

Thanks for the Input. THis one is a bit confusing in that I have no head gasket symptoms and all of this started after the replacement of the pump and draining of the system. I usually say "there are no coincidences".

[SaintC]

For some reason, we are all conditioned to believe that if we have an overheating problem, it must be the water pump or thermostat. Me too.

I was having similar problems with overheating, and replaced all the usual suspects with no luck.

Then I called a mechanic and asked him what he thought the problem was. He asked me if my radiator was over 5 years old. I said yes (it was 10 years old) and he said replace it. Don't rod it, don't clean it...replaced it.

I did just that and I have not had a problem since.

My 2 cents

[eagle12]

I have a 4.3 v6 '90 c/k which had thermostat problems. I was using a seal around the thermostat which I shouldn't have, because it is designed for newer other engines. So it is supposed to sit there loosely in the outlet housing where it would allow the cold fluidto prime untill the hot gets to it. The rtv or gasket which seals the outlet housing walls is supposed to be there only which will allow the thermostat to 'float' in its seat and let some seepage past. I STILL USE THE SEAL BUT I did drill a 1/8" hole in the thermostat flange and it worked swell!! I think I will drill aother on the opposite side because it still seems just a tad slow. Worked to solve this for months!!! Hope it does the trick for you.

[Thunderbolt]

My vote for the original posters problem is the clutch on the fan. Very commom to the C/K's.