Fhead Overheating

This has been an ongoing battle and I'm at wits' end.

No bubbles in the radiator while running, no milky oil, no major leaks (radiator has coolant droplets on the bottom of it), the temperature gauge is accurate and tested against another gauge, the temp. gauge probe is installed in the rear of the cylinder head. I added a bypass to the cylinder head and there's another hose to bypass the would be heater core. New water pump, the fan belt is tight, the fan is facing the way it should. The timing isn't too far advanced. New 160*f thermostat tested in boiling water, it opens and closes as it should, and I drilled a 1/8 hole in it to help with bleeding the system. I have flushed the engine block and radiator separately twice and the coolant is clean. I'm running a 50/50 pre mix coolant. New radiator hoses and they don't appear to be collapsing. The radiator was taken to a shop and they soldered and cleaned it, they also tested the cap and said it was good. I don't have a fan shroud but the fan is ~1 3/4" or less away from the radiator and I can feel it pulling air from the grill. It doesn't boil over even at 220*f on the gauge. Driving around slow is fine but as soon as you get moving down the road at higher speeds (35 mph+) the temperature starts to climb fast.

I've been wanting to replace the radiator since it has coolant seeping from somewhere and am ready to pull the trigger on a new one but I would like someone else's opinion on the matter.

 

What size are your pistons?

 

No idea. I never took the cylinder head off this engine.

 

Its odd how it heats up while driving faster. It looks like you covered all the basics. My only suggestion would be to add a shroud. Have you tried running without a thermostat?

 

Odd. At speed the fan or shroud wouldn't even be necessary. Suggests the overheating is load-related.

Define "overheating." It is not actually boiling - why not? Have you checked actual temps at different parts of the engine? A handheld infra-red sensing unit is $10 and extremely useful for all kinds of work.

Off-the-wall WAG... "since it has coolant seeping from somewhere"..." I never took the cylinder head off this engine. ... A tiny compression leak, under higher engine load, is creating a bubble in the cooling system, and a hot-spot near the temperature sensor/sender.

 

Alternate approach... What was the last thing you did before the overheating issue began? "New" water pump? Radiator "re-conditioning?"

 

Bad head gasket or crack in the head or block possibly. Get your coolant tested for combustion gases.

 

I didn't check to see if the thermostat opened while in the vehicle. I never tried to run without a thermostat. The issue has always been there. I fixed the radiator and water pump because it wouldn't hold coolant. I too suspect an engine problem and might just be trying to avoid it. I'll get the combustion gas tester.

One thing I forgot to mention is there isn't much movement in the radiator. I don't see the coolant moving much even at higher rpm.

 

x2

 

I agree that you could likely be dealing with a head gasket or crack. You also need to verify that the thermostat is opening.

 

water pump...?

 

Agree with baldjosh, if the coolant isn't moving in the radiator, it implies a closed thermostat or a non-working water pump. Did the impeller fall off the new pump when after you installed it?

 

I hope not. It moves some but not much. It looked exactly like the old one. I'll go buy a combustion gas tester. Might be time to get more serious about the firebreather.

 

Maybe the guy at the radiator shop left a shop-rag in it... who knows?

How about a pool... I'm betting on the head gasket or a crack at cylinder #3.

 

Ha, Brutal!

 

Well, the test was a pass. I'm going to pull the thermostat again and run without it and see how it does.



After 4 minutes of pumping instead of the 2 instructed on the package and the engine was warmed and running at 210*F. I also had it at 2k rpm while testing.



Just to be sure I had good test equipment I stuck the tester against the exhaust and pumped on it. Turned yellow almost instantly.

 

The thermostat is working correctly and the water pump is pumping.

 

I know you shouldn't do it, but I can turn the engine over with the fan. I'd think it's tight enough and I do have the correct diameter belt on there.