Coolant drip from transmission/engine mating area

[Mike F]

Thought I'd see if anyone has seen this one before. My car has recently developed a coolant leak. One of those "doesn't show up until the next morning or later" type of situations. I can wipe it dry, drive the car, and let it sit for a while and it seems to stay dry. However, a day or so later I crawl underneath and it's drippy again. The car seems to run fine and I don't have any overheating issues. It is a very slight leak, only a few drips if that. I can't pin down the source, other than to say that it seems to be "wettest" in the area where the engine and transmission meet. It runs along the bellhousing and drips from there. I have checked all manner of hoses and fittings, particularly those that I have replaced over the last several months (return pipe, hot water valve, anything in the VOD area), and can't seem to come up with a culprit. What I haven't done is pressure test while cold; I'm thinking this should probably be my next step, but I thought I'd vet it through everyone here first and see if anyone has experienced this before. Thanks!

Pics (I know it's crummy under there; a good cleaning is on the horizon!):
2397523974


Here's where it eventually ends up. I'd swear my transmission is leaking coolant!
23973

[DMC5180]

Mike,

Take a look at the edge of the head gasket just below the exhaust manifolds. You might have a seeping head gasket. Do you have access to a coolant system pressure tester?

[Mike F]

Dennis-

Inspected that area; all appears dry as far as I can tell. I don't have a pressure tester, but plan to pick one up and run this test. Probably a good thing to have long-term anyway. I've read stories here about people doing this and seeing leaks from seemingly every fitting on the car, so I'm a bit nervous about what I'm going to uncover. This is the first coolant leak I've experienced so far, so I guess it was bound to happen sometime! I suppose if I DO see other leaks it's better in the garage now than on the road later. Any tips or cautions about pressure testing on this car?

[Rich]

...I don't have a pressure tester, but plan to pick one up and run this test. Probably a good thing to have long-term anyway. YES, it is a good tool for any of your cars. I've read stories here about people doing this and seeing leaks from seemingly every fitting on the car, so I'm a bit nervous about what I'm going to uncover. You answered this point in the next two sentences - agree completely This is the first coolant leak I've experienced so far, so I guess it was bound to happen sometime! I suppose if I DO see other leaks it's better in the garage now than on the road later. Any tips or cautions about pressure testing on this car?

See comments inserted above. Get that tester.

No cautions. This car pressure-tests like any other water-cooled car does.

Tips? The pressure cap on the car is 15PSI, so run the test at that pressure to start with. You can do the test cold or hot in case you are looking for leaks that occur in either condition. If you want to check it hot, though, attach the tester before warming up the engine and don't pressure-relieve it until it cools off - same rule that tells you not to pop the rad cap when a car's hot. The pressure-tester will come with an instruction book that explains this and more.

Bonus: You can use the pressure tester down the road to help "burp" air out of the cooling system after a coolant change without warming up the engine , something you need to do every 2 years.

[David T]

See comments inserted above. Get that tester.

No cautions. This car pressure-tests like any other water-cooled car does.

Tips? The pressure cap on the car is 15PSI, so run the test at that pressure to start with. You can do the test cold or hot in case you are looking for leaks that occur in either condition. If you want to check it hot, though, attach the tester before warming up the engine and don't pressure-relieve it until it cools off - same rule that tells you not to pop the rad cap when a car's hot. The pressure-tester will come with an instruction book that explains this and more.

Bonus: You can use the pressure tester down the road to help "burp" air out of the cooling system after a coolant change without warming up the engine , something you need to do every 2 years.

The most common thing to leak in that area is the valve for the heater but it could be any of the connections too. Hard to see from above and even harder to see from below. Pressure test and you will find it. If the hoses are old they should all be changed and if the valve is leaking it also gets replaced. Do not try to stop a leak by overtightening the hose clamps.

[Mike F]

The most common thing to leak in that area is the valve for the heater but it could be any of the connections too. Hard to see from above and even harder to see from below. Pressure test and you will find it. If the hoses are old they should all be changed and if the valve is leaking it also gets replaced. Do not try to stop a leak by overtightening the hose clamps.

I really suspected that the water valve may be the problem, even though I just replaced it. I couldn't find anything on it or the connection points, though. It may very well end up still having something to do with a fitting on or around it.

I picked up a pressure tester this evening. I hope to get an early start tomorrow and see if I can knock this out. I'll update with what I find!

[NightFlyer]

The stock/OEM hot water (aka heater control) valve, and cross-referenced after-market of a similar style, are butterfly valves that have a pivot shaft that penetrates the valve housing. If the internal seals around the pivot shaft are bad, then the valve will leak at that point. Often times, a leak from the shaft will only occur when the engine is cool/cold, disappear upon reaching ordinary running temperature, and then reappear again when the engine has cooled - has to do with the expanding and shrinking of the internal seals. I had such a leak on my car's stock/OEM valve all last year before I managed the time to change it out. I ended up going with a wholly self-contained piston valve, thus eliminating the possibility for a leak from the pivot shaft, as there is none on a piston valve. The only downfall with the piston valve is the possibility of sucking coolant into the vacuum line/system and eventually into the engine if the internal diaphragm were to ever fail - although none of us running the piston valve has ever experienced such a failure. The only bullet proof solution is to either eliminate the valve all together or run a manually controlled gate valve, which are available in a solid brass design.

[DMC5180]

My gut says it's water valve area related. You will need an inspection mirror and a good light source. There is also the Tee fitting that connects the header bottle burp line to one of the heater lines. They are know to corrode thru the T-joint.

First and foremost is getting that pressure tester. 15 PSI will show any week spots. Don't be surprised to see green drips from coupling hoses. Even freshly replaced hoses need checking after a break in period. Rubber hose will cold flow set and lose it's resilience pretty quickly. Cold Flow is the term given to rubber hose when it sets to the distorted shapes from clamping pressure.

[Mike F]

Ok, the plot thickens. I hooked up the pressure tester this morning and ramped it up to 15psi with the engine ice cold. Crawled under the car, inspected every coolant junction that I could see, and found nothing. I gave it another "easy" pump; bringing the pressure to just under 16psi. I thought for sure that this would expose even the tiniest weak points, but again there was nothing. I kept the system pressurized for about 15 minutes, during which it held ~16psi without creep. I was actually impressed at the integrity of the system, since with the exception of VOD stuff and the hot water valve parts, I haven't touched any of it since I got the car. I haven't had any leaks up to this point, but I figured a cold test would expose stuff that normal driving wouldn't.

That leaves me a bit baffled. I suppose I'll drive the car a couple of times and keep an eye on it. Maybe a hot test is worth a try, but like I said originally, the drips don't show up until well after a drive. I also feel uneasy knowing there's a mysterious coolant issue that I can't see; makes me think it will decide to truly show itself when I'm as far away from home as possible. Murphy, you know.

Any thoughts?

[David T]

Ok, the plot thickens. I hooked up the pressure tester this morning and ramped it up to 15psi with the engine ice cold. Crawled under the car, inspected every coolant junction that I could see, and found nothing. I gave it another "easy" pump; bringing the pressure to just under 16psi. I thought for sure that this would expose even the tiniest weak points, but again there was nothing. I kept the system pressurized for about 15 minutes, during which it held ~16psi without creep. I was actually impressed at the integrity of the system, since with the exception of VOD stuff and the hot water valve parts, I haven't touched any of it since I got the car. I haven't had any leaks up to this point, but I figured a cold test would expose stuff that normal driving wouldn't.

That leaves me a bit baffled. I suppose I'll drive the car a couple of times and keep an eye on it. Maybe a hot test is worth a try, but like I said originally, the drips don't show up until well after a drive. I also feel uneasy knowing there's a mysterious coolant issue that I can't see; makes me think it will decide to truly show itself when I'm as far away from home as possible. Murphy, you know.

Any thoughts?

Two possibilities, it is leaking into the VOD and you are not seeing the leak and/or the system needs to be hot.

[jmettee]

Any thoughts?

This one is a bit unique, but when my hot water valve went bad, it leaked a noticeable puddle after a drive. Knowing that the leak was minor after I found where it was coming from, I drove home & noted it was not leaking. While playing with it, I found that it would leak somewhat randomly depending on position of the valve lever. Funny thing was it was not easily repeatable, but I replaced the valve & since then have had no problems.

Note on the pressure tester....they are invaluable on a car like the DMC with so many hose connections. One spring, I pressurized the system to maker sure my water pump hoses were tight after replacement. I didn't see any immediate leaks, but I left it sit for 1 hour. When I returned, I found a puddle (about 1/2 to 1 qt) of coolant on the floor. I was glad to find this before driving around & finding it later on the road.

[DMCMW Dave]

Two possibilities, it is leaking into the VOD and you are not seeing the leak and/or the system needs to be hot.

Typically VOD leaks show up at the back of the car as the valley has a "wall" at the rear of the engine. I'll bet it's a bad water valve or weak connection in that area. What kind of new water valve did you install?

[Mike F]

Typically VOD leaks show up at the back of the car as the valley has a "wall" at the rear of the engine. I'll bet it's a bad water valve or weak connection in that area. What kind of new water valve did you install?

A DMC one, with new hoses and clamps. Did it when I replaced my clutch slave, as removing it made that job a little easier. Figured since I was removing it I might as well replace it, since it had amassed quite a bit of "patina" on it over the years. The only thing I DIDN'T change was the bleed adapter tee (106786), but I got mine cleaned off pretty well. Perhaps that decision is coming back to haunt me! I did that back in May, though, and this leak is just popping up now. I have only driven 163 miles since then, however, so maybe it just took a while. I will pressurize it again, or drive it, and look very carefully again at those connections.

[opethmike]

I just had the EXACT same drip! Was even hitting the floor from the same part of the transmission. In my case:

I have the self-bleeder modification. The leak was coming from the hose splice with T split. So the coolant leak would travel down along that small coolant hose (heater return, I think?), then drip on to the transmission, and eventually on to the floor.

[DMCMW Dave]

We've had to replace a LOT of the bleeder tees, they are very often corroded where the small pipe joins the large one.

[m_w]

We've had to replace a LOT of the bleeder tees, they are very often corroded where the small pipe joins the large one.

I agree. I am putting a new coolant system on my car. Part #106786 had corroded through.

[jawn101]

+1 on the heater control valve or T connector. They are surprisingly easy to damage and are in exactly the right spot to cause the drip you're seeing.

[Mike F]

Thanks for the help! Sorry for my delayed response. Sounds like the bleeder valve is the likely culprit. That being the only thing that I didn't replace on the hot water valve assembly lends more credence to that as well. I didn't see any leaks from there when I did the pressure test, but I definitely know how intermittent and dodgy gremlins like this can be. I have a few things that I need to order and I'll add this to the list. Looks like another "coolant drain" project on the horizon! May be a good opportunity to replace some of the couplers as well...