Hi all.

I am having a little trouble figuring this one out. I have a 1980 Monza with a 350 in it. It runs great but... after running at rpm'* higher than 3000 for any length of time the temp creeps up...and up... and up until it is time to pull over. This might take 15 or 20 minutes. When i open the hood i find the over flow tank is overflowing! Essentially it is pumping all of the water out of the engine...slowly.

If i let it idle... it will run forever( or until it runs out of gas) with no problem, even on the hottest day of summer.

History:
The engine was donated from a car that ran great
I used the same radiator and fan from that car
before i installed it i pulled the heads and had a valve job.

Things i have checked/done:

I have replaced the radiator cap
drained and pressure tested the entire coolant system.
changed the thermostat
removed the thermostat
tried "water wetter"
I installed a temp gage on the inlet side and another on the outlet side of the radiator to
check the temp drop across the core as it was running. I found that it would stay at
180 on the inlet and drop off scale low before it entered the engine again.

Any ideas? I am wondering if it could be developing a steam pocket somewhere (but then when you hear hoof prints don't think zebras comes to mind).

If i got the head gaskets on upside down would that cause it to act this way?
I am just about out of ideas. Soon i will yank it back out and do some exploratory surgery.

Fred: confused:

Sounds like the radiator cap you got is either broken or defective. The engine should very easily be able to hold the pressure. Either that, or you have a clogged radiator or heater core.

it doesn't over heat at idle ???

Is your fan electric or Clutch ?

with air moving through the rad on the road its over heating
but at idle nothing...

Maybe your torqued the heads down wrong ??

its not adding up

Any coolant in the oil ?
if you tromp it does it raise faster ?
then come down a little ?

If your over heating it'* either a clogged water system, radiator, or a collapsed hose. Or teh water pump is bad and not moving coolant. A bad thermostat will over cool, not over heat, water wetter is junk,

If the cap were bad it would still over heat at idle no ??
a bad hose tho... might be ok at idle pressure....

Water pump would give other signs of being bad 9 times out of 10

strange issue and what has me is it isnt over heating at idle

and he said he pressure tested... that would rule out a clogged system wouldn't it

Pressure test only finds leaks, not a obstruction. I'm willing to bet the colant is not moving fast enough to cool when driving, idle needs less cooling. Partially clogged radiator is my guess. Over pressure on top because the coolant can't move threw the radiator.

I am not ruling out a restricted radiator , but it was perfect in the donor car. I put it in there new. it did not see a whole lit of use and looked pretty clean.

the funny thing is that after a drive for 15 min on the highway the water temp was rock solid at 180deg. But when i stopped to check under the hood i found the overflow tank was already starting to fill. i continued on and the tank eventually over flowed. By that time the temp was up around 220. even so, after getting off the free way and driving slowly the temp declined somewhat to around 200, and the tank water was drawn back into the system.

I will have to have the radiator flow checked. but what about the head gaskets? could they be the wrong ones ? on backwards?

Fred

also ...the radiator is a 4 row copper core out of an el camino.

this whole think is making me crazy

clutching at straw here.

That depends on where it gets stuck. I'm 90% sure that my L27 died because of the few times I overheated it during the hot california summer. I replaced the coolant cap, had cooling system flushed, was fighting a upper plenum leak, and turns out the whole reason it was overheating the whole time was because of the thermostat being stuck no more than 2mm open.

That being said, if he'* running the car without the thermostat entirely, it should be running very cold. I think there may be some kind of obstruction.

The head gaskets appear to be symmetrical so installing them either way wouldn't have made a difference.