my75baby

Hello all, I have a problem with my SBC 400 heating up in my 75 vette. The heads have steam holes, the timing is correct, new aluminum water pump, new 3 core aluminum radiator and new 180 stat and temp sensor. I have a 5 blade clutch fan on it now (clutch appears good, only runs on a couple of spins when engine turned off, and cannot be stopped easy with a rolled up paper when engine at idle). Engine is almost in red zone on gauge and goes up and down a little but never below 240. Car does not appear to be overheating but I have to be close. I was going to get a 7 blade fan and put a spacer on it to get the fan closer to radiator (right now its half in and half out of cowl). Any other suggestions? Also the temp sensor is in the head on the drivers side, I originally thought maybe the header was heating up the sending unit pin where the electric connects but I think that is a reach. Since the radiator and water pump is new, how do I burp the system? (maybe there is air in there?)

1972Stingray

I own a 72/350 and I never had over heating problems until I did a rebuilt to the engine and powder coated the entack manifold. I used Thermoglass Exhaust Wrap on every thing, starter and headers and exhaust and it helped. I have the largest aluminum radiator made for a C-3. Wetter Water help and I would check the temperature gauge itself. Check your Thermostat in boiling water does it open and close. I have purchase new ones that did not work. I added a JEG overflow tank between the heater lines to keep a much fluid in the system. After all these changes I have had NO problems in several years.

Indiancreek

Has it run normal in the past? Is it a new rebuild? Any exhaust smell in the cooling system while running? Both radiator hoses hot?

my75baby

It has always ran warm but now runs a little hotter it seems. Since it is the winter now I can only imagine how hot it will run in the summer. Not a new rebuild, just changed cam , lifters, rockers, push rods, timing chain, water pump, and radiator. It may be air in the system but I don't know how to check if there is or how to get it out. If I start the car with the cap off, when it starts to heat up, the water goes down, and then comes back up spills out and goes down again, and then back up and spills out. I don't know if that is normal or not. The car does not overheat into the reservoir tank so maybe the gauge isnt accurate, but I don't want to keep throwing money in the wrong direction.

Indiancreek

Could have a vapor lock!!!! but you said it ran hot ,or warm, in the past. I'd go back to the basics. Compression test, vacume test, and check timing. During the vacume test note the actions of the needle as much as the numbers.
Try taking out the thermostat and cutting a piece of sheet metal the size of the thermostat and drill a 3/4 inch hole in it. Place it in the thermostat housing see what the temp does.
Get your hands on a laser thermometer and check the temps of all the hoses. That is a bunch of stuff to do, but it doesn't cost much. If you do, post it, or send it to me and in the mean time I'll think on it.
What is your oil pressure? Does it drop as the engine heats up? Any odd noises? Put a long screwdriver against the heads someplace or the block while it's running (careful not to get into anything moving) and place the screwdriver against your ear. See if you hear anything odd.

1972Stingray

The up and down is water pump is working. Turn on the heater on high and see if it drop the temp. gos down (an old parade trick). I am guessing air in Heater core and lower block. Air with water become a vapor at temp. To relieve it needs an out. The over flow bottle should have a opening from the radiator to a overflow line to the ground. Now how to to relieve the air is to lower the fluid so the air can escape. That is why the fluid is overflow out the radiator cap. It needs empty space. When you refilled the radiator you should only fill half way to let the air escape. Then add as needed. My Aluminum Radiator is two inches low to take care of air otherwise the overflow bottle dumps it to the ground. My 72 did not come with a overflow bottle. I added a JEG bottle to the right fender near the A/C. I have a 454 overflow bottle but there was not enough space with the different design in AC unit to work.

Mike Ward

Find out first if the gauge indication is accurate. A 60 degree error is not uncommon.

my75baby

Thanks everyone. Well I put an 1" spacer on the fan to bring it closer to the radiator ( I probably could use up to a 2 1/2" but I didn't know how much room I had until now). I also drilled 1/4 inch steam holes in the stat. Car runs MUCH cooler, only gets about 230 now at its highest then goes down to around 205-210. It is still a little high for my liking though. I do not have the hood on right now b/c of the work I did, will putting the hood back on make a difference too? Maybe the design aides in air circulation? Would a 160 stat be better than the 180 I have in there now, or would that make it worse?

73, Dark Blue 454

What he said. Go to Sears and get an infrared temperature gun ($60 for the Craftsman) and point it briefly at the thermostat housing and hoses, both in and out.

You'll have a better understanding of what's going on with water temp.

If you have a big variance between what the gun and guage are reporting, you likely have a problem with with either the guage or sender. And my guess is the gauge.

Zip sells a great looking AC Delco gauge for your 75:

http://www.zip-corvette.com/ProductD...GR-SR&CTitle=&

You could wire it up with jumpers before installing to see if the new gauge is reporing more accurately, before tearing into the instrument panel for a gauge swap (not fun).

What sending unit are you using; the factory original?

Also, what "3-core" aluminum radiator are you running?

Lasltly, have you ever poured any stop-leak product into the cooling system?