350 Won't Stop Overheating
 

Have an overheating problem with the rebuilt 350 in my 1-ton. I'm at wits end trying to figure it out, has to be something simple. Hoping someone here may have an answer...

350, bored .030 over with a Melling MTC-1 Cam and 333882 heads
New stock water pump
New 180-deg thermostat (this is the 3rd thermostat this week we tried).
New thermostat elbow
New radiator hoses top and bottom
Radiator was new about 6-8yrs ago (has been flushed during all this, clean as a whistle, even looking in with a flashlight, no buildup).

- I was able to run the engine for the cam break-in without the thermostat, the pump is pushing coolant, and the engine did stay cool for the break-in run.

- But as soon as I installed the thermostat, it overheats... every time. The pass side of the rad is getting hot (where the heater core cycles through) and the drivers side is cool.

- Confirmed that the thermostat is opening when hot by removing the rad cap, blowing back through the top rad hose towards engine and having the coolant rise/spill over rad fill.

- The radiator fins are clean, the fan is spinning, belts are tight, fan clutch is good, rad does have a fan shroud.

- I've tried leaving the rad cap off to purge it, rigging up a bypass line from pump to intake manifold, pinching off the heater core, pulling different intake plugs or hoses to burp it, etc.

So before I go buy a new radiator, or do something drastic like pull the engine apart... anyone got any ideas?

Re: 350 Won't Stop Overheating
 

How hot is hot? boiling over? That is weird that the radiator is cool on one side.

Re: 350 Won't Stop Overheating
 

This may sound crazy but is your timing advancing correctly when the advance is hooked to vacuum? The radiator temp difference does seem strange though..

Re: 350 Won't Stop Overheating
 

Also it's not sucking a hose flat when thermostat is in and cap on ??

Re: 350 Won't Stop Overheating
 

Got hot enough to boil for a brief minute in the top hose once... I didn't run it as long thereafter so nothing would be damaged.


Believe so, though I will double check tomorrow. It's currently set to 8deg, when I plugged the vacuum advance line back in there was a significant difference, but the mark stayed at 8 last I remember checking...

Negatory on the flat hose, maintains form.


So, I seemed to have licked it. Was a bad (brand new) thermostat of all things. Pulled it out of the truck and put it and another new thermo in a pot of water. (Both are 180's). The new one opened at 180+/-, the other from the truck didn't until the water began to boil heavily.

That's makes 4 brand new thermostats I went though this week until I got one that worked.

Re: 350 Won't Stop Overheating
 

What year is this and do you have a serpentine belt system or V belt. I'm thinking wrong water pump

Re: 350 Won't Stop Overheating
 

It's an '88, still the square body style. Has a serpentine belt but not the setup like the GMT400's. Still turns in the same clockwise direction as the V-belt setups.

Re: 350 Won't Stop Overheating
 

I'd be very suspect of the water pump having the wrong impeller in it. Even with the wrong impeller it'll still look like its moving coolant, its just not able to move enough volume.

Re: 350 Won't Stop Overheating
 

Glad you finally got a good (New) part.

Stuff like that just adds to the issue.:uhmk::sumo::chevy:

Re: 350 Won't Stop Overheating
 

Same thought crossed my mind too... I originally put a new high volume pump on figuring it would only help. Ended up ordering a stock volume pump and changing it out thinking the high volume was too much or wrong impeller.


Thanks, me too!


One last thing... anyone have recommendations for a rebuilt engine break-in procedure? I went for a short 3 mile drive today. Planning on changing the oil before I go on a longer drive tomorrow afternoon.

General consensus online seems to be don't do anything but regular driving, no hauling for the first 500 miles. Maybe 1-2 more oil changes before then.

What do you guys think?

Re: 350 Won't Stop Overheating
 

After you (Think) the Cam is broke in :lol:

You can Drive it like you stole It.:metal:

Just vary RPM a whole lot.
Don't hold it at at certain RPM.

I would keep RPM's under 4 grand for a while:ito:

That's if you can keep your foot out of it.:chevy:

Re: 350 Won't Stop Overheating
 

2nd driving it like you stole it. Did that with my now spare motor (150k plus since the rebuild) (spare motor because truck it was in rusted beyond reasonable repair). Had the heads off around 100k due to popping a head gasket and the cylinders still looked good with visible cross hatching. I did not baby that engine at all, still ran great when the truck it was in got retired and will end up in my GMC when its engine is too tired.

Re: 350 Won't Stop Overheating
 

Thanks for the reply guys... keep forgetting to check back here.

Been driving around for a week now, have to advance the timing a bit more. Seems to be lacking some top end umph on the highway at 2800-3K.

Hauled a Ford 8N carcass home in the bed last week, been driving around with it since (too heavy to unload with my small Kubota, have to disassemble). Truck doesn't seems to notice an extra 1K sitting in the back. So far so good!