DRE69L46

Disappearing Coolant – Where’s my radiator fluid going?

I’m hoping one of you folks can give me some advice. I have a 1969 Corvette L-46 with a 350 ci /350 hp motor. The motor is original, and has never been rebuilt. It has 50,000 miles on the odometer.

I’m losing about one ounce of coolant every mile. Here’s what I know.
- There are no coolant leaks under the car, or inside. The overflow hose from the expansion tank isn’t leaking fluid out. No leaks from hoses.
- The engine starts, idles, and runs normally.
- There is no evidence of coolant in the oil. I just changed the oil, and it was pure.
- There is no evidence of oil or gasses in the coolant. It’s clear and uncontaminated.
- I pulled four spark plugs, and they look ok, but this coolant problem is new and hasn’t been going on for long.
- The radiator cap is fine. I’ve tried two, and I’ve pressure tested them.
- When I pressure test the coolant system, I see that I’m losing about 1 psi every two minutes, indicating there is a leak somewhere. There are no visible leaks when I pressurize the system.
- Today I noticed some pooling of coolant around the bottom of the intake manifold, on the passenger’s side.

So from these symptoms, I’m guessing that there is a small leak in the intake manifold gasket, that would suck coolant into the intake. I think it must be getting burned in the cylinders in a small enough quantity it’s not apparent when the engine is running. If this is the case, then I think I would pull the intake manifold and replace that gaskets. I’ve never done this before, but I’m assuming it can be done fairly easily with the motor in the car.

Any advice or suggestions on testing to determine the problem and on possible solutions?

Thanks very much, Doug

myk7

Is the pooling happening on top of the intake? or where the intake meets the head? If it's on top of the intake, I would think the fluid is coming by the intake bolt threads... pull one at a time and clean and coat with some rtv and reinstall.. might be all it needs.

73, Dark Blue 454

I guess it would be possible for coolant to get past the intake gasket and make it's way into the intake port of the head but it would be very unusaul. Is there any white smoke from your exhaust?

To help diagnose, pull all the spark plugs then pressurize the cooling system. Put a Q-tip on the end of a wire then insert the cotton end into the chamber and see if it comes back green.

I'm hoping it's not a small crack in your double-hump heads.

Let us know.

1972corvette454

Slight leak from your heater core? check the passenger side carpet, hopefully it's not wet, it it is, then it's your heater core starting to leak like mine did.

wombvette

I would look at the water pump. It is common for a small leak out of the weep hole to be hard to see until it gets bad.

drwet

I would replace the intake manifold gasket, however. I have not found leaking intake manifold gaskets to be that unusual, especially with aluminum intakes. Several of the intake manifold bolts do go into coolant passages, so it is important to put some kind of sealant on the threads.

7T1vette

Could be a crack in the block near a water passage or it could be a head gasket that is about to fail between water passage and a cylinder. I would hope for the head gasket.

74modified

Make sure the easy stuff is ruled out before tearing into it.

msandym

I have same thing , I think its the thermastat housing
gasket on my car .

flyeri

Last time this happened to me it was the head gasket. It was sucking water into a cylinder when it was running. Not a drop got into the oil.

Doug1

same as on my wife's 350, I Bought some Barr's leaks head gasket "fixer" from walmart, almost $30, it fixed it