BoulderGeek

So, I drove my car for 40 miles or so, yesterday. Got it up to temperature and explored the drivability of the new DME EPROM. Never took it over 5500 RPM.

I had brought coolant level up to MAX in the expansion tank, a few days earlier. I had noticed that coolant wasn't up to the minimum line, even at rest when warm.

After I returned, yesterday, I hooked up the battery to a battery tender (noticing that I was running at 12.5V with all of the lights on). With the hood up, I noticed that my coolant was back down below MIN.

Topped up again with 50/50.

No evident coolant leakage. No drips. No white smoke, nor any color smoke in exhaust. Just passed Colorado emissions testing with flying colors. Oil is still translucent, no milkiness nor anything amiss by inspection.

I've had plenty of Japanese cars with head gasket and water jacket leaks. They kicked huge antifreeze smoke. No smoke nor smell, here.

So, my question is, where do you think the coolant is going? Is such a thing normal for 944s? Cooling system leak with evaporation, but no drip?

divil

Maybe the seal in the expansion tank cap? But I'd get a pressure tester and check for leaks anyway just in case.

KevinGross

Fill to the MIN mark when cold, should rise to roughly the MAX when hot. If you overfill it, coolant will push out the overflow port in the tank. Not sure you don't have a leak, but try this first.

BoulderGeek

What I am finding is that if it is between MIN and MAX when cold, coolant is sucked into the cooling system when the engine is running. On shutdown, it will expand back up into the tank. While running, the expansion tanks seems empty.

Operating temperature remains consistent at ~40% up the gauge.

Could be boiling off a bit, I guess. Opening the expansion tank cap when warm results in an overpressure release hiss and coolant level rising. So, it seems the tank cap has a good seal. Weird.

V2Rocket

check the water temp sensor crush rings, they might be leaking...mine sure are

thomasmryan

I find it easier to find small leaks by pressurizing the system with it drained of coolant.

7psi and a spray bottle with soapy water will find the little external leaks. Rubber hoses corrode castings and fittings over time so a little hylomar in the joints keeps them tight.

KevinGross

Do you smell coolant in your exhaust? Sweet smell, often you can see white vapor. You may have a head gasket problem given your description.

BoulderGeek

Thank you for all of the constructive advice.

I will check all of these things.

I assume I need to remove the belly pan and search from below?

Kevin, the car has surprisingly clear exhaust. It was in the low fractions of permissible particulates and gasses when emissions tested two weeks ago. It passed the Fast Pass easily. No smell from the exhaust, but, come to think of it, after I did a coolant top up, I got a light antifreeze smell in through the under hood HVAC vents.

Perhaps there is a leak when in motion that is wicking off and not dripping when stopped?

thomasmryan

Yes, that gravity thing. Try not to exceed 8-9psi when you pressure test.

mytrplseven

If you're unsuccessful at finding anything using the above procedures, I'd recommend going to the auto parts store and getting a fluorescent dye leak test kit. They're cheap and using the "magic flashlight and glasses" you can go back over the engine, under the dash (HVAC) and under the front of the radiator areas and the leak will show up as a colored tracer. You should run the car for about 1/2 hour to get a good trace. The dye won't cause problems with the coolant or the rest of the car.

BoulderGeek

Pick up a can of "Stop Leak" while I'm there?

We're going away for the long weekend, but i will roll it up on the ramps soon and pull the belly pan to see what's what. Grr.

Just looking at the Lindsey Racing $90 all radiator hose kit. Worth doing proactively, with a flush, if it is a seriously used car?

mikey_audiogeek

Heater core is leaking in mine. Might be worth checking?
Cheers,
Mike

thomasmryan

Save your money on the snake oil and pick up a pressure tester with the cap adapter. Personally, I like to find the problem, it's cause and perform the correct repair. These cars are precision machines and like to be treated as such.

If it has no apparent external leaks after testing the system, your head gasket or oil/water heat exchanger would be suspect. Napa has a test system for hydrocarbons in the coolant that is less than 20 bucks and a seal kit for the oil housing is 35 or so.

When I purchased my car, the air bleed on the radiator was the main culprit.(new one) The second was the upper radiator hose where it attached to the block (hylomar). When those held pressure, the next weakest part was the oil housing that dripped one drop overnight under 7psi. (Seal kit) The last item was the end cap on the radiator. About 50 bucks total. Runs below the first hash mark and coolant level has remained steady for a year.

SloMo228

Absolutely. Do all of the hoses, too. I recently replaced my radiator hoses (but not the harder-to-reach heater hoses) as preventative maintenance, and not a month later one of the heater hoses split and started spraying coolant while I was driving. Now I have all new hoses.

Odds are your coolant hoses are original. It's only a matter of time before they give up the ghost. I'd replace them all just for peace of mind that the coolant will stay put where it's supposed to be.

Jfrahm

If you are losing that much coolant it should be easy to track down. I would not spend a dime until you know what you are dealing with. Maybe leak detection dye if you find a leak and want to see where it's coming from, but the free rental of a pressure tester might sort that as well.

1 - Validate the test. Make sure you are filling it properly and it's not overfull when hot
2 - Check to see if it's dumping coolant when parked up hot (bad radiator cap)
3 - Look for one or more steam cleaned spark plugs
4 - Rent a pressure tester to find a small leak that becomes a big leak when driving. A small water pump drip will often pour coolant under pressure.
[I rented the one at the Advance Auto on 287 and it works but the tank fit is not great, I needed to use the universal fitting which blew off a few times, maybe try a different store but that one can be used if need be.]

Leak detection dye is pretty great but IMO for when you have a seep from somewhere and you want to see the location more exactly. The flashlights can be had from Ebay very cheap straight from the Far East if you can wait a few weeks. You have to clean things up and look for the appearance of the dye. If you just dump it in and drive around the coolant and dye might get sprayed all over and you do not learn anything.

Cheers,
-Joel.