Need help finding coolant leak

[MrShorty]

My '92 Explorer has been using coolant for some time now. I've tried on various occasions to figure out where the coolant is going, and I've reached the end of my abilities. Here's what I have done.

I borrowed a cooling system pressure tester from Autozone and put that on the radiator cold. I pressured it up and found a slow leak from the radiator. Replaced the radiator. Leak at the radiator is gone.

Still using coolant, so I borrowed the pressure tester again. Leaking where the heater hoses meet the heater core. One of the nipples coming off the heater core was deformed, so I replaced the heater core. Leak at the heater core appears to be gone.

Still using coolant. I pressure up the system (cold), and try as I might, I can't see any sign of coolant coming outside the engine. I've looked at the usual places, hoses, clamps, gaskets. I've left the system at pressure for an hour with no sign of coolant dripping off the engine. I'm using like a quart a week, so I would think I should be able to see any kind of external leak.

I've checked the oil, and the oil doesn't show any signs of getting coolant in it. I've pulled one of the spark plugs (#5) and don't see any obvious sign of coolant deposits on the plug.

I'm stumped. How else do they find coolant leaks? I've heard of "smoke" tests that can be used to find leaks, but I've never tried one, nor do I know if the equipment is readily availabe to the DIY'er.

Basically I'm looking for more ideas for locating the leak myself or what to ask for at the repair shop to help get this resolved. Any help would be appreciated.

 

[SuperEx91]

First of all, I would pressure test the vehicle with the engine at operating temp. this is when everything happens(most of the time). Let it warm up. throw the pressure tester on it and turn your heater on. this will allow coolant flow into the heater core and everything related. If you are loosing pressure and you see no drips on the ground, change the oil and watch it drain. you wont always see it on the dipstick. If none is found, thenit is probably getting burned. if that is the case, it would probable be burning in only 1 or maybe 2 clyinders so ckeck all the plugs if you havent. you can also watch for bubbles coming up to the radiator fill. if the head gaskets blown or head is cracked, copression may be leaking into cooling system. last resort, check compression on all cylinders or try a cylinder leakdown test.

 

[shamaal]

Oddly enough I only saw oil in my coolant never water in my oil. Just a drop of oil on the water when I drained it. Symptoms of bad head gasket may vary depending on the volume of the leak, from steam in the exhaust to a drop of oil in the radiator.

 

[Glacier991]

I would second the suspicion that you have an intake manifold gasket leak at a water passage.... it is not an uncommon leak in the Explorer.... I'd check all plugs to see if you might localize it.

 

[shamaal]

Ooh! I get to use my manifold leak picture. The car places also sell fluorescent stuff for coolant, but unless you got a visible leak somewhere, I'm not sure how much value it is. I've got a bottle I've never used.

 

[MrShorty]

I don't know why I didn't do this before. Last night I had my pressure tester hooked up to the hot engine, and wasn't seeing anything. While it was sitting, I thought, "I've heard of people finding "snot" under the oil cap. I wonder..." Took off the oil cap and, sure enough, there are a few "balls" of "snot". It looks like I know where the coolant is going now. So the next question is, which gasket is leaking? Intake manifold, cylinder head, cylinder head cracked (I sure hope not). Thoughts on isolating the leak? Or does one usually just stop diagnosing at this point and start tearing it apart.

 

[shamaal]

Cylinder compression tests are a handy diagnostic. Write down the readings and look for the one(s) that is/are out of family by >10%.

 

[NHale623]

Are you sure those balls of snot aren't condensation? What does the oil look like, a choclate milkshake? If you're losing a quart of coolant a week into your oil pan, I am fairly certain you would notice it.

 

[MrShorty]

I'm not certain it isn't just condensation, now that you mention it. Considering we spent nearly two weeks below freezing,it's possible. The oil on the dipstick looks normal brownish/black like it normally looks when it's ready to change. No sign of "milkshake" on the dipstick.

 

[NHale623]

Shamaal has a real good idea, a compression test may be very telling.

 

[BryanB]

I should have joined earlier. Had I known coolant leaks from the intake gasket were common, I could have saved a bunch of money. I had been fouling the first plug on left bank and filling the radiator for over a year. I finally got sick of it and took it in. The Intake gasket was perfect! I looked at it myself.(I do have a strong automotive background, just no time and a non-heated garage!) Stumped and fearing the worst, I opted for a Jasper re-man engine.

 

[MrShorty]

finally got a round tuit and did my compression test 150-160 across all cylinders. None of the spark plugs showed any obvious signs of burning coolant.

Somewhat out of desperation, I took it in to my regular mechanic. He pressure tested it and he couldn't find any leak either (he was kind enough not to charge me for the "2nd opinion").

Also out of desperation, I checked the transmission fluid. No sign of coolant mixing with the ATF. I didn't expect to see anything; if it was going through the transmission, I would have expected to see other problems by now.

While visiting with the mechanic, I asked his thoughts on where to go from here. The basic idea was to perform "exploratory surgery" (kind of) and tear it down to the intake gasket, replace, and reassemble to see if that fixed the problem. I've been a little uncomfortable with this idea because I'm the kind of guy who likes to get a "diagnosis" before attempting the repair. On the other hand, to borrow a phrase from Mr. Spock (just recently watch Star Trek VI), "When all possibilities have been disproven, whatever remains, however unlikely, must be the solution." (or something to that effect). Basically, it isn't leaking out of the engine, it isn't going through the oil or the transmission, so what's left? through the combustion chamber, right? And that's either intake or cylinder head, right?

I've almost convinced myself to go ahead and do the intake gasket. Anybody have any thoughts? Are there any instruments out there that can detect coolant in the exhaust? or ???

 

[rmcknight]

try watching the sides of the radiator, its quite common for water to leak from either side bucket, as over time the large o rings on the buckets (plastic sides) shrink, and in the transition stage from cold to hot (under engine pump pressure), these can leak for about 30+ seconds.

 

[MrShorty]

It's a brand new radiator, so I hope it isn't the radiator. Is this something you've seen be completely undetectable in any kind of pressure test? It was using coolant before the new radiator, and is still using coolant, and no pressure test reveals any external leaks. Is there a trick to finding this particular leak that I'm missing? If I can show that it is the radiator, then the rad shop owes me a replacement.

 

[rmcknight]

it probably isnt the rad. whats the chance of 2 bad ones!
but the pressure test may not find this type of leak if its due to the plastic expanding during warm up.
bring it up to temp with the rad cap off, rev the engine up hi for 30 seconds - and watch for any air bubbles in the rad. if there you have a blown head gasket, otherwise either a radiator / heater / thermostat housing / pipe. If none of those, then you may have a crack in one of the heads (bloody alloy!), if not that then its leaking into the 4th dimension.

After you discount the rad, i would replace all the rubber hoses on the entire vehicle, including the long heater hoses and see how she runs. If there are any heater vacuum valve leavers in the line, check the rubber inside that as well.