KingD

I have a 1966 327 350. I pulled the original motor and replaced it with a '66 327/250 bored 0.030" and put in a slightly larger cam. All new bearings, gaskets, bolts all torqued to the specs. It has about 500 miles on the rebuild.

I replaced the radiator with a new Harrison radiator, hoses, water pump, and a 160 degree thermostat (yeah, I know it calls for a 180 degree, but put this in after the 180 did not work at first).

After running for about 15 minutes, the temp slowly climbs up to 220 - 240 at idle before I shut it down.

It stays at 160 when cruising at 60 mph. Once it idles or is in stop and go traffic, it climbs right up to 240+ in a few minutes.

I tested it in my garage and at 15 minutes it read; gauge - 220, out of the intake manifold and into the top of the radiator - 205, into water pump from radiator - 208.

I would think the fluid is not circulating in the radiator, but I drained it and put in fresh antifreeze mixed with distilled water. All travels through the radiator and expansion tank okay.

Before the rebuild the original engine and setup did not over heat.

What can I do?

Dennis

Sky65

Put the 180 back in. The thermostat controls the minimum operating temp not max. I would be sure all air has been bleed out out of the cooling system. Check timing, initial, vacuum and mechanical. Make sure your vac advance is hooked to manifold vac. Also your new engine may need more initial advance than the old one.

Tom

Powershift

Although I am not as strong as SKY65 regarding the thermostat. 180F is ideal, but a 160F should work as well, especially during the summer.

I would also concentrate on the radiator area. Is the proper fan shroud in place, perhaps even consider the air conditioning radiator seals and shroud extension. Check the location of the fan blades in the shroud, also the condition and temperature setting of the fan clutch.


The 327/250 is more prone to air entrapment in the block than the 327/350, so make certain you double check for any air. You can pull the thermostat housing (again) and fill everything from this point to get air out.

What water pump did you use?? A lot of the cheaper rebuilds use a stamped impeller which may not be as efficient as an original cast impeller.

I'll probably think up a few more things to check tonight, and can re-post tomorrow. Others will also add to this.

Larry

JohnZ

Do you mean a DeWitts stacked-plate aluminum restoration radiator, or something else? It makes no sense that your I.R. gun shows 205*F into the top of the radiator and 208*F out of the bottom of the radiator; you should show 25*-30* of cooling between those two points.

Powershift

Unless all his cooling air is bypassing the radiator.

PS: I can still remember the radiator on my 1965 BB MOPAR. 4 blade fan, direct drive, and no radiator shroud. It was fine in the summer if you stayed above 40 MPH, but in stop and go traffic at idle you were a sitting duck. FWIW

Larry

KingD

The 180 thermostat did not perform any different than the 160. Yes, a new DeWitt's Harrison radiator.

The fan blade and shroud are original and worked great before the rebuild. How do I know if the clutch is performing? It spins and moves air from the radiator across the engine.

I purchased the water pump from Corvette Central.

I will check and be sure to pour more coolant into the thermostat port. But, if the coolant is flowing won't the air bubbles end up in the expansion tank?

KingD

How do you bleed the air out of the cooling system. That may be the issue.

I do have the vacuum advance connected and have checked/set the timing before and after connecting the vacuum.

GUSTO14

The best way is to simply drill a couple of holes (1/8th - 3/16") in the outer rim of the thermostat to allow air to equalize on both sides of the thermostat. It won't significantly effect the operation of the thermostat, but will aide in keeping air from getting trapped.




Good luck... GUSTO

wombvette

Classic symptom of not enough air flow through the radiator at low speeds.

KingD

Drilling a hole in the thermostat may take care of it, but it seems to diminish the purpose of the part. If it did not come this way from the factory, then how did GM solve this problem without drill bits?

KingD

The temp rises faster with the rebuilt engine than the original engine. Does a larger cam make that much of a difference?

Nowhere Man

Run the engine to operating temp with the radiator cap off That will burp the system and let all the air out. Drilling the t-stat is fixing a problem that never existed

KingD

Will remove the expansion tank cap and run it today. Sounds like a plan. Thank you.

Powershift

Make certain to install and lock the the cap before shutting the engine down. If coolant gets to over 200F (or so) and you shut the engine down with the cap removed, the coolant will boil over from the expansion tank or radiator due to residual heat in the block and no coolant movement..

This normally does not happen with a 160F or 180F thermostat installed, but will with a 195F thermostat or if you are having cooling issues where the engine temperature is up.

A 327/300 engine (or 250 HP engine) has a tendency to pocket some air in the system. I should eventually work its way out as Nowhereman stated above, but to make certain, fill thru the thermostat housing or drill a 1/8 inch hole in the thermostat if none is provided. I have a few GM/DELCO NOS thermostats for our cars, and they actually have two small slits in them to vent off any trapped air. Not certain all thermostats made today are like this.

It sounds to me like your main issue is airflow across the new radiator when idling. So I would concentrate on this area. As JohnZ stated you should see a 20F temperature difference (at least) across the radiator from top to bottom.

The hi-po cam may also be contributing to the problem. Therefore you need to pay more attention to airflow across the radiator and ways to improve it. The AC components I mentioned earlier are a good start.

What parts were re-used from your old engine and what parts were bought new?? If a new fan clutch was purchased, it may also be a source to the problem.

Larry

BD104X

You said you went with a larger cam, but you reset the timing. With an aftermarket cam, your factory timing specs are null & void. You may need to retard the timing a bit.

Powershift

The distributor vacuum can may also not be correct or working properly if the vacuum is different. The entire distributor initial + centrifugal + vacuum advance curve needs to be checked and verified. An incorrect vacuum can may contribute to the hot idle issue.

Larry

GTOguy

I agree with wombvette. There is not enough air going through the radiator core at slow speed to cool the engine. Never mind thermostats and air pockets. If these were the problem, it would be running hot going down the road, big time. The fact that it only gets hot in traffic means it's an air flow/fan issue.

Powershift

I also stated this back in Post #3 and #5 and #14....and said it was the most likely cause. However, there may also be some other issues at play here. Particularly idle vacuum and engine vacuum advance and timing. Trying to cover all the bases for the OP as he may have multiple issues.

BD104X

What you're saying makes perfect sense, but OP said he was not overheating until he made changes to the engine. If the engine is running hot to the point where a correctly operating cooling system can't keep up, you will notice it at low speeds first when there isn't enough airflow to mask the condition.

GTOguy

Agreed, Powershift. I just kept seeing pictures of drilled thermostats and had to say something!