Now It's My Turn for Help
 

I am having a serious overheating problem which just started last week. Here is a chronology:

Thursday evening: Nice and cool. Took the car out. I was out on the interstate and noticed my temp gauge was pinned! Made it back home with the cap screaming like a tugboat.

Friday: Checked the water and topped it off. Idled the engine and it seemed fine for 25 minutes or so. Shut it off and let it cool. Checked the water level and topped it off. Started it and ran it up to 150 deg. Took it out to the interstate. It was running between 150 and 180. Ran it through the gears getting on the highway. Just after that the gauge went up as fast as a gas gauge when filling the tank. Made it home again with the cap screaming.

Sunday: Pulled the water pump and it seemed fine. It is a Milodon high volume aluminum pump. Everything appeared ok. I pulled the 160 deg. thermostat and cycled it in boiling water five or six times. No problem.

I backflushed the radiator and block and there appeared to be no obstructions.

Monday: Spoke to Milodon. They said it could be an air pocket and to make sure when I fill it to have the car on an incline and check it once or twice to top off.

Tuesday: Re-installed the water pump and a new 180 deg thermostat. Filled with water. Jacked up the front of the car and continued to fill. Started it up and kept topping it off till I felt it was full. Idled it for a bit and it went up to 180 deg. Shut it off and topped it off again. Installed new Stant 25 lb racing cap.

Took the car out on the highway. Initially ran at 180 deg for about 4-5 miles. Made a U turn and ran gently through the gears. Watched the gauge drop from 180 to about 160 and then, suddenly, shot up to 250 in less than 2 miles.

Any ideas,
Roscoe

Roscoe,
Do a pressure test on cooling system to make sure you don't have a blown head gasket.

RD

Cranky,
Thanks....I'm planning on doing that tomorrow.
Roscoe

been there
 

Rosco, I'll bet big it's a head gasket. If the pressure test is negative still do the chemical test of the water.:(

Ditto on the head gasket theory :(
A slight blow-by of high pressure gases, especially when the engine is revving, creates a air pockets which in turn prevent adequate cooling and cause an overheat condition. Been there done that. I hate it!!

Might also be a cracked head. Hopefully its a head gasket.

Drill a 1/8 inch hole in the top of the thermostat, this will eliminate any air pockets. Make sure the hole is not obstructed by the gasket.

I'm leaning toward the gasket. No coolant in the oil. Will pressure test the system today.

Pathenry: I am using a balanced thermostat which came with the hole already in the flange. No gasket needed with CSI billet water neck, it has an 'o' ring.

Roscoe

Roscoe--

It looks like you have received a lot of good advice as to the cause of your problem. You went with the obvious-- the thermostat -not the problem and no obstruction in the cooling system(or is there?). I do not know what you are using for a lower hose or how old it is but with that high volume water pump you may want to consider the possibility that you are collapsing the the lower hose under high rpm conditions - running through the gears. I hope your problem is not the head gasket or worse yet a cracked head. Let us know what you find.

ERACER I

Eracer,

Thanks, The lower hose has a coiled spring in it to prevent collapsing. The heads are aluminum and they usually don't crack as easily as castings.

Roscoe

Roscoe

I have seen the coil springs in the hoses collapse. A new lower hose is a cheap dx and fix if its the problem.

Eracer,
Something else to add to my list! Thanks,
Roscoe

Roscoe, sorry to hear of your troubles my friend! You can check the hose manually, but I think thats a real long shot. I don't buy the air pocket idea just because of the history. Sure sounds like a blown head gasket....sorry! :CRY:
Jeff: love the avatar, but a V6??

427,
Yeah....it's a *****. Bill K. is on his way over with a pressure tester and dye for the coolant. Will know shortly.
Roscoe

OK,
we did a leakdown test on the cooling system and only a slight lb per minute drop.

We did a pressure test and, when running, we developed no significant pressure (1 lb) with no fluctuation on revs.

We did a dye test for emission gasses in the coolant. Negative

Now we noticed that the radiator (Griffin) is cool on the bottom half, although the hose running back to the pump is hot.
Could it be a clogged radiator????

Roscoe

The radiator being cool on the bottom half could be clogged. But I think I would try running it with out any thermostate at all just in case there is something hanging up the movement of the termostate when it is in place. I know you tested it in water and even replaced it but temporarily removing it would be easy enough.

Have a very similar setup. 351W, TFS aluminum heads, Edelbrock hi vol water pump, 180 deg thermostat, Griffin rad, Scotts 16" fan. Used stainless 1 3/4" exhaust tubing for lower water crossover with 3, 90deg elbows. Using a 7 pound Stant cap. Temp runs 180 while cruising, gets up to 205 when fan kicks in.
Also using coolant overflow bottle because engine "breathes".

My first thoughts would be head gasket or cracked head. Any white smoke coming out either exhaust?

We're getting gas (steam or air) into the cooling system, which gets into the water pump, pump looses prime, and no water flow. Or blockage in the radiator if bottom of radiator is cold when engine is running.

Mine was a mutha getting all the air out of it when first fired up.

A test. With garden hose keeping system full, take the upper hose that comes out of the thermostat fitting. Hold it up in the air. With engine running, idling, what should be coming out is water. No water? Pump isn't pumping. Water and bubbles? Gas is entering cooling system.

Next test. Set the plug wires up so you can remove them one at a time with a plug wire removal tool. Insulated. Hook up a tune up tach. Remove plug wires one at a time. RPM will drop. This should be a constant drop except the leaking cylinder. It will drop less. And, the bubbles should stop, or decrease.

Let us know how this works out.

Okie: Thanks for the tip. That's one we will try today.

Jack: Thanks for the advice. No smoke at all, anytime, coming out of the pipes. None of the tests we have done point to a head gasket.

We are going to do a leakdown test on all the cyl's today. We will try the garden hose test also.
Thanks,
Roscoe

Sorry to hear of your troubles. My instincts tell me (at this point) to suspect the thermostat. Mine came with a 180 'stat and last night crept to 190. Not critical, however I like to have more of a "buffer" particularly with the concern about air bubbles we have. Might I suggest dropping in a 160 thermostat, at least for a test run? A $4.00 thermostat is a cheap stab in the dark. Best of luck, nice to hear you have consistant, healthy compression. JT

JT,
We will probably try it without a thermostat. My original thermostat was a 160 and cycles well in boiling water. I thew in a 180 to replace it.
Thanks for the advice,
Roscoe