Often when I park the car the radiator will start overflowing. The temp doesn't get any hotter than normal, but as soon as i park the car fluid starts spewing out of the overflow tube.

Eventually there won't be enough fluid to keep the engine cool.

These are cool days that I am having the problem. 75 degrees or less

A friend suggested that it might be a head gasket. He said the leak could be creating too much presure in the cooling system.

I was sort of hoping it is just a radiator cap.

What do you guys think?

thanks,
~Jay

 

Replace the radiator cap (with the correct pressure rating). That's a cheap diagnosis.

 

If you keep filling up the reservoir tank, it will always over flow. The tank should be about half full, not full.
Don

 

I should have been more detailed.. there is reseroir tank on my car. But I normally only fill the radiator up to about 4" below the top.

I called Tom Dewitt who was very helpful, and I'm affraid it may be a blown head gasket causing the the cooling system to become over presureized.

~Jay

 

sounds reasonable too me bummer for you though. If I lived closer I'd help ya pull the heads.

 

I was gonna say head gasket too. BTW, make sure you have Mk IV, not Gen I

 

What is the difference between the two?

thanks,
~Jay

 

well... good news,

I took the car to a shop and the head gasket tested out fine

The tech suggested a new cap (even though it tested out fine), And also suggested adding an overflow tank.

I guess in the I have a weekend project.

Do you have any other suggestions?

thanks,
~Jay

 

The water holes are not the correct size & misaligned. If you have the original style BB, it's a Mk IV & it will overheat with the wrong head gaskets. The Gen V engines came out in the 90's with revised cooling passages. The early Gen V gaskets were not compatible with the Mk IV, but I believe the current style Gen motors have been modified to work with the old style Mk IV head gaskets (That's the info I got from Scoggin-Dickey). In any case, if you don't solve your problem you might want to pull the heads off to check/replace the gaskets.

 

I have the same problem and running a 13psi cap, I have a 15psi cap on order which I hope will solve the problem. I should have the cap early next week I will let you know what happens to the overflow problem

 

First, find a radiator shop that has the tester to check for exhaust gas in the coolant. Have them test if it is present then you have a head gasket problem and both need to be replaced. You may have used the wrong gaskets for the block and heads or have an exhaust leak. Either way I have a bbc in a 73 and don't see how you can pull the heads with the engine in the car. Moral - hoist time.

Second, see what temps the t-stat is opening at. Get the digital temp gauge and see when it balances, if it does.

Third, use the digital temp gun and see what temps you are running at with engine is warm and idleing and then when you shut it off what the hot soak temps are. A head gasket leak into the exhaust will usually cause the temps to keep rising as the heated exhaust gas overcomes the ability of the cooling system to cool. The other symptom is exhaust gas will usually cause very high pressures in the cooling system and when you shut it off - it puks in the overflow tank.

Diagnose before you dig in .

 

Often people mis-understand the function of a radiator cap and the concept of pressure. The cap does not control the pressure in the system, it limits it. Think of a pressure cap the same as you would that little relief valve on your hot water tank at home. It never opens, unless something is really wrong, and then it pops open, preventing the tank from blowing up. Well the same thing works on a radiator. Pressure is "created" by the FLOW of the fluid and the RESISTANCE to that fluid. As the temperature increases, this pressure will rise slightly but typically it runs about 5-7 psi. So, with a 13-15 psi cap it should be doing nothing, just like the relief on your water tank. If for some reason the cooling system isn't doing the job, the temperature will increase and this will increase the pressure some more until it reaches the cap setting and blows, limiting the sytem pressure from damaging the components. But as long as you're below, say 220, this isn't going to happen and it doesn't matter if you had a 10, 20, or a 30 psi cap.

In the case of this thread, Jay told me the fluid looked "foamy" and the only way to do that is with air. And it's not from re-filling. Something is "pumping" the fluid out to the half full mark and it's not running hot. I'm going with the gasket right now.

 

I just replaced the 13 psi cap with the 15 psi, (correct for aluminum system), the puking tank no longer pukes. The temp stays at 180 highway or city traffic. This seem to be the solution to my problem, it was worth the try. One side note, it tends to show the weak heater hoses, they are probably in need of replacement anyhow.

 

Just fixed this problem today.... VERY CAREFULLY take the radiator cap off while the coolant is hot. Use a heavy towel over it while you losen it. Putting it back on while the coolant is hot, and at its most expanded state, this fixed this problem for me.

 

What does your cooling system look like? Do you have a cap on the radiator? Do you also have a metal expansion tank? Where is your overflow hose? For starters, I would (and did) install a plastic tank at the end of the overflow hose so at least it won't dump all over the ground... or your driveway.... or your garage. I was having this problem for a while, but I have since cooled things off and don't even get any coolant into the overflow tank.

 

My Wifes car had a problem, in which the coolant would flow to the overflow tank,yet when the engine cooled off the vaccum was not pulling it back into the radiator. The hose from the rad. to the tank had a pin hole. IT WOULD NOT spill out fluid But it was enough so the vaccum could NOT pull the fluid back in once it was cool. PS I would fill the rad to the top and let the overflow tank handle it,it should puck out after shutting down then pull it back in. If after a few cycles there is air in the rad. I would look at this hose

 

the system is a aluminum expansion tank with cap and a overflow hose from the neck of the filler on the tank.