rebuilt c1 overheating

[Randy M.]

I have been struggling with this overheating problem for 4 months now. I have a fresh rebuilt numbers matching block. Heads are from a 77 305 Camaro. New aluminum radiator. Rebuilt water pump. Rebuilt wcfb carb. I have the engine timed to factory specs. Engine runs great for ten minutes and then temp climbs above 240 at water neck outlet. I have an infrared gun. If I let it run it will boil over and blow lower hose off. This is with 50/50 mix of water and antifreeze. The body is off the frame.

Here's what I have tried: Pulled heads and checked all passages for obstructions. Replaced head gaskets. I tried a different water pump. Flushed engine twice and replaced fluids.

I'm thinking theres something blocking a passageway and is not letting water where it should be.

Any further ideas before I break the engine down all the way?

[Duke W.]

Re: rebuilt c1 overheating

Year? Engine option? Does a new aluminum radiator mean an exact OE replacement or a non-OE aftermarket design? What about the fan? OE?

How about the spark advance map? What's the total idle timing?

You need to provide a complete description of the configuration including any thing cooling system related that is not OE or exact OE replacement. This includes the spark advance map.

Duke

[Steven C.]

Re: rebuilt c1 overheating

Not to be a smartass, but I've just resolved an overheating problem by replacing a bad cap.

Also, the part you mentioned about "blowing the lower hose off", sounds like you might be getting compression through the cooling system...will contribute heat as well, would be more of a problem after t'stat opens. This could range from valve timing issues to head gasket to cracked head/block.

Steve

[David N.]

Re: rebuilt c1 overheating

Steve,

Have you checked the thermostat to make sure it is opening correctly?

David Nims #16939

[John O.]

Re: rebuilt c1 overheating

Randy

Most of your problem is you stated the body is off the frame. When I had my body off the frame and ran the motor, I was only able to run it a few minutes.Then it overheated. You have no proper air direction.Get the body back on and if all else is correct, I think your problem will be solved.
Just my 2 cents.

John

[Randy M.]

Re: rebuilt c1 overheating

John - I have a high speed industrial fan 5 feet away from front. I have checked thermostat. It's opening. I tried another just to be sure. I also tried no thermostat.

[Randy M.]

Re: rebuilt c1 overheating

Duke - thanks for you your interest. Its a 58 230 hp engine. THe radiator is from DeWitts. Stock fan. Yes, I have it on the correct way. Timing is 4 degrees btdc at idle. Distributor is rebuilt stock unit. Thanks.

[Rod Wagner #27060]

Re: rebuilt c1 overheating

The blowing off of the lower rad hose is a problem. Sounds like combustion gasses are getting in the cooling system
I would put a pressure tester (the kind that you can pressure test a cooling system with) in place of the radiator cap and pressurize the system. If it doesn't hold the pressure (15 lbs or so) for at least 15 minutes, you have an internal coolant leak somewhere.

[Chuck R.]

Re: rebuilt c1 overheating

Hi Randy,

Silly questions,

Do the water passages for the heads match the block?
Are the gaskets lining up with the ports on both the heads and block?
Is the fan clutch performing as it should?
Could there possibly be flush plugs in the radiator pipes to keep crap out while being shipped that might have been overlooked and not removed?
Hey I had to ask

You should number one, check out why the cap isn't popping off first. That's a ton of pressure building up there Randy!

These cooling system designs revolve around air being forced through a sealed radiator fan shroud and core support to plow as much air as possible across the radiator's fins. That's why all the seals surrounding the radiator, the fan shroud and the core supports are emphsized so much.

Is the fan shroud in place? If not, there's a major air flow issue right out of the gates.

If the shroud is in place and the fan blades are a little more than 1/2 way into the shroud, then I'd lay a large box fan onto the core support to feed as much air as possible through the radiator. If the engine runs and doesn't throw fits, then I'd say you have it narrowed down to air flow.

Once I repaired an overheating station wagon for a guy that had just gotten it out of the shop for a leaky radiator. Come to find out, guess who his ex-wife's new Bo was? Yep, ole lover boy the mechanic stuffed a chunk of clear plastic bag into the lower tank of the new radiator. That took about an hours worth of head scratching to figure that one out.

I'm a hairs breathe away from putting the spark, fuel and air to my project while it sets on the bare chassis, so I would be very interested in reading what you find, so keep me in the loop ok?

I hope it's simple Randy,

Chuck

[Mark B.]

Re: rebuilt c1 overheating

Randy, Have you checked the proper installation of the head gaskets? They can be installed upside down or backwards and cause problems with the coolant passages. Also, set your initial timing to 10 to 12 degrees BTDC. You'll notice a BIG difference in temps and the overall engine idle and acceleration. Carb running too lean. You'll need to adjust it after you reset timing anyways, so use a vacuum gauge to set the idle mixture to the highest vacuum reading with the vac advance port plugged. Good luck.

[Duke W.]

Re: rebuilt c1 overheating

Does it have vacuum advance at idle? That's why I asked for the "total idle timeing." That is the timing measured at idle with the

VAC connected.

Just because initial timing is per spec says nothing about whether the timing at all engine operating conditions is correct. Initial

timing is just a value that is added to based on manifold vacuum and revs. Together these are the "timing map".

You have one independent variable - total spark advance - and two independent variables - manifold vacuum and revs. Together

they determine how much spark timing is provided under the virtually infinite number of engine operating conditions, and just

because initial timing is correct doesnt' mean that total timing is what the engine needs. You need to understand the vacuum and

centrifugal spark advance curves, and it's also very important what signal source the VAC receives. If you plot the timing map on a

X-Y-Z graph, you get a "surface".

The OE specs for vacuum and centrifugal are a good place to start, but can sometimes be improved.

So you need to know the VAC ID number, its specs, and whether or not it meets spec. This can be done with a vacuum pump and

dial back timing light, but just checking total timing at idle will usually let you know if the VAC is properly connected and reasonably

within spec.

If there is no vacuum advance at idle to increase timing beyond the initial value, overheating is a likely result.

Duke

[Duke W.]

Re: rebuilt c1 overheating

Idle mixture must ALWAYS be set in the normal configuration, which means the VAC must be connected. Assuming the VAC is signaled by full manifold vacuum at idle, you connect the vacuum gage to the VAC signal line with a tee.

Duke

[Mike M.]

Another way to run the engine

When I ran mine with the body off, I didn't use the rad. I looped the top water pump connection to the lower. Ran a garden hose to the heater hose connection on the engine and another hose to let the water run out on the other heater hose connection. You control how hot you want the engine by how much you open the tap on the hose. You need the fan belt on the water pump to help circulate the water. It worked great ran the engine for 30 minutes. This way may rule out a few things that could be causing your problem.