Edwardsd1

I'm finishing up a rebuild with my Chevy 350 (86-88 350 block with 305 heads) and I'm having over heating problems. I replaced the heater core (it was leaking before) and the engine temp gauge (I lost the last one it had before the rebuild), I had a shop check the head gaskets and they said they were fine (and there is no coolant in the oil). I spent an afternoon putting in coolant, running the engine (getting the coolant through the system) and every time it still started to over heat (always went over 210 and half way to 260) and on my last go round I revved the engine to around 2000 a couple of times, to make sure it was still running smoothly and then coolant started pouring out of where the heater core is. I thought maybe it was coming out of the hoses. I've worked through the same process today, even tried to "burp" the system until coolant started boiling over the the top of the radiator. The heater core didn't leak at all today, but the engine is still getting too hot. I don't have the thermostat on. Every time I run it and then let it cool the coolant level goes down a little. Any suggestions?

kevinkpk

You need a tstat in as a flow restrictor, else the coolent will cycle to fast and not cool in the radiator. The tsat has to work, check it with 190 deg water on you stove, drop it in, it should open. Also need to know air conditioning, ect.? You can bypass the heater core by tying the inlet, outlet together if you suspect a leak in the core.

Edwardsd1

I've taken the air conditioning off completely, but I'll want the heater to work (I live in Texas, but I'm planning to take my truck to school in Minnesota next year, where I will certainly need a heater). So, should I just drain the system again, and then put the thermostat back in? Also, I'm hoping there is not leak in the heater core, since I just replaced it, and it hasn't leaked since the one time it did yesterday. I've also been doing all my testing in a hot garage (doors open of course), might that have an effect?

kevinkpk

If you suspect the heater core is leaking, you can bypass it. I'd take a piece of 3/4 copper pipe, and bypass the core. You need the restriction in the return to radiator as stated the flow without it will not allow retention time for the coolent in the radiator to dissepate heat.

joes_place

you may want to recheck your ignition timing

kevinkpk

1) If the heater core is leaking, you will have "steam" out the vents in heat or defrost, and or coolent on the floor board.
2) Does this have a clutch fan?
3) Reinstall the tstat.
4) Setting in a garage with no air flow (other than fan?) anything will eventually overheat. Check your fan, if it had a/c it had a temp controlled clutch fan, that thing should be turn faster than the engine.

Edwardsd1

The heater core is not leaking any more, I think it may have been to much pressure and it leaked out of the hoses since I didn't have the heater on (I didn't know you were supposed to do that when refilling the system, kinda new at this stuff).

It does have a fan clutch, which I can spin with relative ease for a number of rotations, so I am going to replace it.

I have re installed the tstat

I'm becoming a little concerned that when installing the heads I have have put the head gaskets on backwards, blocking the coolant channels ( I really hope not, but I accept that it is a possibility).

Edwardsd1

The engine is still over heating, sitting in the garage, no hood on (and of course the garage door is open). I've replaced the radiator cap, fan clutch, water pump, and had the radiator rodded. The thermostat was tested (it began opening at around 180degrees, which is what it was rated for), and reinstalled. I've set the timing at 4degrees advanced (according to my Haynes guide it should either be 4degrees or 8degrees). I'm thinking of taking it a shop to see if they can figure something out (maybe use an infrared thermometer to possibly pinpoint a part of the engine that may be getting hotter than they others). Any other suggestions?

kevinkpk

So this thing is running in a garage without air movement? Untill it gets airflow through the radiator I cannot help you.

Edwardsd1

Just got back from a 5 minute drive. Still over heating.