My son's 87 L98 started overheating and his biological father replaced the thermostat and radiator cap while he was visiting him. It still ran hot and was boiling into the overflow pretty quickly so I put a 160 deg therm and another new radiator cap on since I have bought some that were just crap.

Per forum info, I pulled the radiator, flushed it, cleaned the critters and straightened fins and same with AC condenser, removed debris and scrubbed plenum, replaced both hoses, refilled and burped. Still same thing. Now I'm thinking blown head gasket.

Right about the time I was going to take it to my mechanic I kept thinking everything is leading me to the radiator cap (Mr Sam Adams whispered it in my ear) so, I crimped the ears on the new cap a little and burped it some more to try one last thing before I spent more money and problem solved.


Turns out the plastic spout was worn enough on the back side to not hold the cap close enough to pressure up. It did take quite a while to burp all of the air out once I got it to pressure up.

EDIT:
It has occurred to me that I have not posted the information which led me to my conclusion. Once the engine neared operating temps, the radiator would begin to boil over into the overflow. I could lightly apply pressure on the new radiator cap and it would quit. That should have told me enough but I was not connecting the dots out of frustrations and confusion. By crimping the tabs on the new radiator cap it made up for the worn plastic on the radiator fill spout and held the cap close enough to allow it to properly seal the system and prevent the coolant from escaping into the overflow.


Hope it helps

 

Interesting problem.

Thanks for taking the time to post this.

 

Why did you install a 160 thermostat? That won't do anything to the coolant temp. The stock thermostat was wide open and the 160 will also be wide open. Finding out why the system couldn't get rid of heat was the correct thing to do. The cooling system is under 15 psi pressure to increase the boiling point and does not aid heat transfer. Cleaning the radiator and condenser fins will make the big difference.

 

Now you tell me!!!

 

If your stock thermostat wasn't stuck closed, then installing a lower opening temp stat will not cure overheating. System pressure has nothing to do with overheating. Clogged fins DO have an effect on heat transfer and can cause overheating!!!!!

 

Take your radiator cap off and see how long it stays cool. If the cooling system cannot keep coolant in the system it won't matter it you are using a milk jug for a radiator.

 

jfb, thank you for the information. My experience with working on vehicles is always a learning process and your info will be useful the next time.

 

I only posted this because I did a fairly comprehensive internet search for possible solutions to the problems my car was displaying and did not find anything relating to the solution I ended up with. I just wanted the next person banging their head against the wall to have a little more information than what I had.

I am a disable Marine with limited physical abilities and can't do a lot of the things I used to. I also have to admit to the fact that the meds the VA has me on interferes with my thought process and somewhat skews logic. I deal with it and do what I can but it does add to frustration level. Even so, I always try to rely on myself before I am required to spend money to have someone else do what I cannot.

I was following what someone else had already started and it has been my experience not to trust what someone else tells you. I automatically default to "undo what someone else has done".

I agree I did not do enough on my part to correctly troubleshoot once I was faced with the task. That's what happens when you get one shade tree mechanic following another shade tree mechanic's work.

Anyone looking for a possible solution to their overheating please check the plenum for debris.

No debate this was the original cause to the overheating that lead to the actions that someone else took which ultimately compounded the problem. The information I was going on was second hand and after the fact. I was getting confused after performing the recommended actions. It was still overheating but apparently with different symptoms than it started out with and I did not know the original symptoms.



I always eliminate the most obvious and inexpensive possibilities first and thermostats/radiator caps are cheap enough to just replace. There is still a limited heat transfer even if the fan is not on if the coolant is at least circulating. It has been my experience that in 100+ degree ambient temperatures that the sooner the coolant begins circulating, it at least begins to transfer some of the heat away from the engine sooner.


In hind sight I now come to the conclusion that the radiator cap (on the car when the original symptoms started) already had the modification done to it that made it correctly fit the worn plastic fill spout on the radiator. I had know way of knowing this and don't see any reason why someone else would think of it either.

 

Thanks for your service.



And, again, thanks for posting this ... it may help the next person.

 

A thermostat opening sooner (lower temp) does absolutely nothing to the final operating temperature during overheating. The coolant temperature settles at the temperature where the radiator gets rid of heat as fast as the engine makes it!
When I read that someone tries a 160 F thermostat to help their overheating problem I try to educate them about how automobile cooling systems work without giving a course on thermodynamics or heat transfer AND without insulting them. My efforts are rarely appreciated (not directed to you)! I sincerely hope your overheating problem is fixed. At least it isn't intermittent which are the hardest problems to fix.

 

jfb, I appreciate the input. I took auto mech in high school way back in the 1900's but mostly retained enough to keep me off of the side of the road and do minor repairs to save myself some money. It's definitely a perishable skill that needs refreshing. I sincerely meant that your information would be useful the next time and I do appreciate your taking the time share your knowledge. It will help me and others who read this thread.

ghlkal, thank you for the props!!

 

You could easily replace it. My local NAPA had one in stock for $120. It is just about the least expensive part to replace on a Corvette.