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Coolant Leaking from Oil Pan Gasket


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Hey Everyone,

I Parked the jeep (88 MJ 4.0, AW4) after a quick trip this morning and returned 30 min later to find a sizable coolant puddle forming. I dropped under in the hopes of finding a loose hose clamp and to my dismay it appears to be leaking from the oil pan gasket... How or why would this be happening and am I facing potentially serious problems?.. An oil pan gasket would be a simple fix and I could get at my lazy rear main seal while I'm at it but I am concerned that there may be some internal damage for coolant to be squeezing out of the oil pan. My oil level and pressure are normal and my coolant has no signs of oil in it. Havent drained the oil yet but I suppose I'll get on that.

Thanks in advance for your help

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:eek: WOW !! Man i hope its just running down the front of the motor then across the oil pan's lip. IMHO I would pull the dip stick to make sure it wasnt full of antifreez it will show up on the stick it might not be green but it will be wet or even look really milky. Till then i wouldnt run it till i knew it wasnt in the oil pan. Was it running bad or kind of under powered before hand?

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It wasnt running great but no noticeable change in power or idle quality in the past few weeks. This is the first time Ive seen it leaking. What am i facing do you think? Cracked head? Its not smoking on startup or under power either.

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Look at the white stain on the front cover, its from coolant running down the front of the engine. what you are seeing is coolant that has accumulated on the oil pan rail and isnt coming from the pan itself. if it were it would mixed wirh oil or the area would be oily. Probably water pump or thermostat housing. :D

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I'm thinking soft plug or maybe waterpump. Did you think with your dipstick Jimmy ?? :rotfl2: Sorry i love that slogan

I would think you would notice some sort of power loss if it was the head gasket :dunno: Did you check the oil?

Anyone eles have any ideas

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That would be a huge relief. With the amount of coolant under the truck though I would expect that white stain to be fresh and green. I'm off work in 2 hrs and I will start investigating. Also now that you mention it garmj, my thermostat housing has excessive rtv sealant around it. I wonder if the PO half-assed a replacement and didnt get a proper gasket and I never caught the leak...

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If your oils not milky, its not coming from the oil pan, and if it was, it wouldnt be pretty green. Start at the front top and work your way down. Front edge of the oil pan is the near the bottom of the water pump. Just replace your water pump and thermostat and youll be good to go. Seeing that its coming from the front of the block, its probably not a freeze plug. You should be able to see all the freeze plugs except for the ones behind the flywheel/flexplate. Water pump/tstat is my informed guess. Or you could clean off all the green coolant, and then pressure test the system with a hand held tester, and see where the leak starts and go from there.

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I would bet water pump. With fresh green like that, there is no way that it is coming from "inside" the oil pan. That looks to be coming from the bottom of the water pump and running along the lip of the pan.

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Thanks for all the help guys. I did a pretty thorough scan of the whole block and bolt-ons and have found the culprits. (1) The PO appears to have skipped a legitimate thermostat gasket in favor of rtv sealant which has failed and is now leaking. (2) more serious and annoying: the first casting hole (freeze plug?) looks pretty oxidized and leaks a pretty steady stream when the engine heats up. I'm relieved to say the least. Thanks for helpin me not tear apart my oil pan in search of serious damage.

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Soft plugs (freeze plugs)are rearward of where the stain and coolant are, coolant never migrates to the front of the engine due to gravity and air blowing coolant towards the rear. Coincedentially I replaced the waterpump on my MJ this weekend and found I also had a pin hole in the thermostat housing. White stains are a good indicator of a leak. Good Luck

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