454 Losing Coolant

[Mike T.]

Re: 454 Losing Coolant

Mark E - I had completely put together my response and then tried to attach a couple pics but I'm still having problems getting my 'upright' pics to not post sideways. I don't have this issue on any other forum and have tried Mark F's suggestions but still 'no dice'. So, once again, apologies for having to look sideways at my pics but hopefully the writeup will help.
On to the response - Yes, there is a way. Stant and other mfr's make cooling system pressure testers. My 66 NOM BB roadster had a body-off many moons ago and looks very fresh but as we all know, Corvettes can sometimes sit around with little or no use and that causes problems.
When I got my 66, it had the typical issues for a car that sits for long periods and those included a carb that was leaking front and rear, a water pump that was in need of replacement and a heater core that was leaking profusely. Notice all these parts are related to fluids?
Once I got the car in good shape and running nicely, I noticed that with no leaks to be seen, I might take it out for a drive and long enough of a drive that it was fully up to operating temperature like say 180-185 but when I got home, it invariably spit out some coolant. At first I thought the coolant level might have been a bit too high since it's supposed to be a couple inches below the filler neck on the Radiator (no expansion tank on a 66 L72 in this instance). Got that squared away but it still would kick out some fluid right after shutting down and meant to include that 180-185 temp seen on the dash gauge was verified by an IR gun. Started to check things and used my Stant pressure tester on the repro 15# radiator cap and voila...it barely held a pound or two. Replaced it with a new (and pump verified) GM cap that holds a full 15 pounds and no more coolant coming out the overflow hose. This pressure tester can be used on the cap or radiator, doesn't matter but the difference is, when you connect it and pressurize the radiator, there's lotsa things downstream that can be potential leak sites like the radiator itself, the radiator hoses, heater core, heater hoses, water pump and coolant passages throughout the engine. So, when checking at the radiator, it will be a bit more difficult to nail down exactly where the leak is...if you do see a drop in pressure. One last thing, the actual connection at the radiator neck (or radiator cap if that's what's being tested) can be the leak point. Make sure you have a good seal. Okay, so now for the two twisted pics...sorry again.IMG_1094.jpgIMG_9268.jpg

[Mark E.]

Re: 454 Losing Coolant

I understand I can pressure test the cooling system.

My question is there a way to locate the leak... right head, left head, intake...

I also understand after running the engine for awhile I can read the plugs for evidence.

But what can be determined before putting the car together and starting it?

[Mike T.]

Re: 454 Losing Coolant

That's when it'll take a bit of detective work. The pressure tester will possibly tell you it's not keeping pressure and from there, then it's time to pull the plugs, mark them so you know which cylinder they came from and inspect them. Just like my 66 L79 Coupe that 'mostly' ran good before being stored for '5' years and then finding out that coolant had made it's way down into the pan, those cracks in my cylinder heads were probably present when we bought the car meaning there was 'some' coolant already going into areas it wasn't supposed to 'before' it really showed it's ugly head.
Besides pulling plugs which I suspect might show you where the smoking guy lays, you could do compression tests of each of the cylinders and see which one is noticeably on the low side. There's also a leak-down test that will also be done to each cylinder and expect again, that if a cylinder (or more) are compromised, it should show.

[Mark E.]

Re: 454 Losing Coolant

Update on this coolant loss:

A few of months ago I pressure tested the cooling system as suggested. Three external leaks were found: two lower radiator hose clamps (for its metal extension tube) and one outbound heater hose clamp at the pump. After tightening those clamps the system maintained pressure. I then topped off the coolant, changed the oil and filter (no apparent coolant seen but I didn't test it), and primed the engine since it hadn't been started in a long while.

Since then, it's been driven about 200 miles with no coolant loss or change in oil level, and the system maintains pressure. The increase in oil level while in storage remains a mystery so I'll keep a close eye on that. Right now, I'm keeping my fingers crossed while enjoying the car.

BTW, the pressure tester I bought to do this test found these leaks immediately. The hose clamp leaks were slow enough during storage that coolant residue was not readily apparent, but all started dripping immediately when pressure was applied. This was a worthwhile $60 tool; I wish I had gotten one long ago.

And thank you to all the folks who provided advice.

[John P.]

Re: 454 Losing Coolant

Hello Mark, If you have access to a borescope, you can remove the plugs and inspect each of the cylinders. You can remove the distributor and inspect the underside of the intake with the borescope. You can also remove the carburetor and check inside the intake runners for signs of leaks. A pressure tester as shown above would greatly increase the chance of detecting the leak. First loosen the drain plug and see if you actually have coolant in the pan. As stated before, small leaks at hose connections are common on cars that are stored for extended periods, and the leaking coolant often evaporates before detected. Additional oil drainage from sitting along with any condensation will show a higher oil level.

[Timothy B.]

Re: 454 Losing Coolant

How about the head bolts, many if not all go into the water jacket and they should be sealed when assembled.

[Duke W.]

Re: 454 Losing Coolant

Update on this coolant loss:

The increase in oil level while in storage remains a mystery so I'll keep a close eye on that. Right now, I'm keeping my fingers crossed while enjoying the car.

.

The best time to check oil is with the engine hot a few minutes after shutdown, and the surface the car is on must be level or very nearly so. A good time to do this is at the gas station. Before pumping the gas remove the dipstick, wipe it down, and lay in a convenient place. This will allow the oil in the dip stick tube to drain down. Then insert when you're done pumping the gas and paying to check the level. If you remove and immediately replace the dipstick you can get a false reading.

Initially upon shutdown there's a quart or two still up in the engine, so allowing a few minutes before you check let's most of it drain down, but there could still at least half a quart up high, and over months of storage most of this drains down.

You can verify by checking and documenting the oil level a few minutes after shutdown prior to storage. Then check before you start the engine after the storage period and you will very likely find the oil level is higher.

Duke

[Mark E.]

Re: 454 Losing Coolant

You can verify by checking and documenting the oil level a few minutes after shutdown prior to storage. Then check before you start the engine after the storage period and you will very likely find the oil level is higher.

Duke

I'm hoping this is what happened here. I'll recheck as suggested. Thanks again Duke.

[Mark E.]

Re: 454 Losing Coolant

How about the head bolts, many if not all go into the water jacket and they should be sealed when assembled.

Good thought. This engine was overhauled in 1989 with no loss of coolant until recently. So I'm hoping this isn't the issue now, but will keep and eye on it.

[Mark E.]

Re: 454 Losing Coolant

Hello Mark, If you have access to a borescope, you can remove the plugs and inspect each of the cylinders. You can remove the distributor and inspect the underside of the intake with the borescope. You can also remove the carburetor and check inside the intake runners for signs of leaks. A pressure tester as shown above would greatly increase the chance of detecting the leak. First loosen the drain plug and see if you actually have coolant in the pan. As stated before, small leaks at hose connections are common on cars that are stored for extended periods, and the leaking coolant often evaporates before detected. Additional oil drainage from sitting along with any condensation will show a higher oil level.

Thanks John. If the engine continues to mysteriously lose coolant I'll look into these checks.