Hi All, I'm still overheating!!! It's a 68 conv, rebuilt 289, and Itried a 160 and a 180 thermostat, 3row radiator,2 new caps,tried flex fan and stock fan, back flushed it, shroud. I'm at a loss here. Funny thing is it won't overheat at idle, but on the highway!at idle the temp goes to 160 andstays there. I'm wondering ifthevacuumadvance is a factor. When I rebuilt the motor I didn't replace/rebuild the old distributor (did petronics), but it's definitely working as if you remove the hose the timing changes. Is it possible that it's not advancing enough (or too much) and that's why it's only overheating at higher rpm?? Is there a way to test it?Thanx

 

It could be timing or fuel mixture or a combination, maybe minor detonation. Has the radiator been professionally cleaned?

 

Have you put in a new lower hose?

Overheating at speed is indicative of a blockage in the system. 'sometimes' the lower radiator hose can collaspse.

 

Yeah, I think you may have timing issue. Do you have it hooked up to ported or manifold vacuum? Should be ported and when you unplug it at idle you should not see a difference.

 

There should also be a spring in the lower radiator hose as well.

 

+1 for all above post.

I have to ask ....how do you know its overheating? Could it be a faulty gauge?

Can you get a non contact thermometer? (barrow one??) Take a reading of the top of the radiator VS the bottom of the radiator (How much difference is there?)

Take a reading of the thermostat housing (is it above 180?)....How much?

-Gun

 

Just got my 72 rag back from the shop who rebuilt my motor. Same symptoms you described. There are2 things I have learned over the past couple of years. 1) Working on my 68 Cougar. The fan blades MUST be half in and half out of the shroud you installed. If not adjust by cutting, or adding spacers. 2) Working on this Cleveland that is in the rag. It must have a water restrictor plate. But the problem with mine WAS, the passenger head gasket was put on wrong. Adn had blcoked the water ports.

Would set and idle all you wanted, but as soon as you took off driving it would overheat, discharge the water. You might consider that if it has been opened up.

 

It is not timing. Head gasket or some sort of blockage seems more likely. Run a pressure test to see if the system is holding.

 

I would suspect something more significant than timing. Some sort of restriction
that effects higher rpm more than idle. Head gasket, correct water pump etc.

Jav

 

I was thinking this, but was debating on whether to say it yet....

This could happen easy enough.... almost happened to me and I knew better. In the process of assembling the engine the head gaskets went on and off a couple of times, and I think someone might have been playing around with one of them as well.

In any case, after setting one of the heads in place, it had occurred to me that I did not "visually inspect" the head gasket placement just prior to placing the head. Took it back off and guess what... it was backwards... almost tragic...