random overheating
 

Hey guys i have had an issue with random overheating for a little while. It happens both at an idle stop and driving. its a very gradual overheating and i think the thermostat is working cause the upper radiator hose is hot and ive changed it out twice. I am running two electric fans and an aluminum rad, and pretty much the only thing i have not changed is the water pump. does this sound like it could be the culprit?? its a 454 with what i believe is a 4 core rad ( i dont know how to check this) and im not sure what the fans are rated at but they are pullers and seem to pull through quite a bit of air. my timing has also been set recently... any suggestions on where to start?

Re: random overheating
 

First I would check the gauge. Have you verified that it's correct?
Not that a new pump can't be bad, but how old is the water pump?

Re: random overheating
 

The gauge is only 2 months old and its mechanical, also i know its overheating cause it spit my overflow cap off and spit antifreeze everywhere! the pump came of an 82 that i pulled for parts, thats why im leaning towards that being bad. Im just not sure cause i always thought that if your overheating at a stop you have airflow issues and if you overheat while driving you have waterflow issues, i overheat doing both! thanks for the help!

Re: random overheating
 

Before replacing the pump, I'd take it in to a shop to do a leak down test on the radiator to see if you have a head gasket leak somewhere.

I had a similar issue on a Chevelle I used to have. Gradual increase in temp and eventually spilling out the cap. IIRC, mine turned out to be a hairline crack on one of the heads.

On some but not all radiators you can look in the cap opening when engine is cold and see the bubbles.

Re: random overheating
 

i did a pressure test on the rad a month ago and it held pressure fine but i guess i should just rent it again to double check. and i just took it to a shop last week, they didn't do a pressure test but could not duplicate the overheating, only overheats when im around! SOB!

Re: random overheating
 

One other question: do you have an overflow container?

My 68 overheated on me until I installed an overflow tube.

Re: random overheating
 

yes i do, and i also put a new line on it also, it blew the cap off of it though so i need to find a new cap!

Re: random overheating
 

anyone have any recomendations for who to buy a water pump from? or if i could rebuild it myself? i haven't seen any online other than high performance stuff and dont really want that.

Re: random overheating
 

You cant rebuild the water pump yourself. A brand new one is too cheap to even try to bother with it. Just make sure you buy a NEW pump and not a rebuilt pump. The rebuilt pump will likely leak as soon as you bolt it up to the engine.

Re: random overheating
 

I agree with above recommendation. The old ones with all the screws all around used to be rebuildable with a new gasket. But now they're cheap. A few years ago I paid $15.

One other thing: sure seems to me that you're building up a lot of pressure. I'd definintely do another pressure test.

And to check the water pump: One thing I've did on another vehicle is remove the thermostat and fill the radiator. You can see the water circulating without having to wait for it to warm up.

Re: random overheating
 

Are you sure the radiator cap was any good and that it is a 18 psi cap for a closed system. Also make sure your coolant is in good shape and not over protected.

Re: random overheating
 

Have your cooling system checked for CO2. If theres CO2 gas in cooling system you have a blown head gasket or a cracked head. I use a co2 detecting dye kit from Matco. But there is a backyard method... if you have a battery powered co2 alarm in your house, warm the truck up with the radiator cap off, put a funnel in the radiator neck then place the alarm in the funnel, if it goes off you have combustion gas in the cooling system.

Re: random overheating
 

Unless there is a huge build-up of sludge or rust on the impeller, which is not likely, water pumps do not "fail" to pump water. The only thing that can really happen is bearing failure (which makes noise) and seal failure (which causes a leak). Water pumps just don't miraculously quit pumping.
They are not "positive displacement" pumps, like an oil pump. It is simply a "propeller" that is in the water and "suggesting" that it should move.

As far as checking for the amount of cores. You simply look through the radiator cap hole. You should see the ends of the cores, if you can't see them, that is part of your over-heating problem.

Re: random overheating
 

Alright!! Thanks for all the great info guys. Looks like ill start with a pressure test and then the c02 test and hold off on changing the water pump for now as its not leaking or squealing. I have a bad feeling it’s a head gasket :banghead: