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My 2007 4.0L has developed an oil leak, but I'm having trouble figuring out where it's coming from. I'm the original owner of the car. Only about 75,000 miles on it. Noticed an oil spot in the driveway after the wife left for work. Worried it was the rear main, I put the car up on ramps and started tracking it down. Seems it's running down the outside of the bell housing of the trans from the rear of the engine. There is oil pooled up at the rear of the valley between the heads. It kind of looks like there's a plug of some sort where an oil pressure sensor would be on a traditional/older V8, and maybe that's what's leaking? Or could it be a head gasket issue? Or something with the intake manifold? It doesn't appear to be a valve cover gasket. My driveway is on an incline, so I suppose it's possible the leak could be anywhere under the intake, and pooling at the rear when it's parked.
Are there any common leaks like this with these engines that I should be looking for? Any suggestions before I pull the intake and start looking?
Update: I looked around the front of the engine. The timing chain tensioner is clean, no leaks, but the thermostat housing is suspect. It has definitely had coolant seeping out of it at some point. The car has always lost a little coolant between oil changes, so maybe that's that. Could that also be the source of the oil leak? Does oil run through the thermostat housing?
Well, I haven't done anything yet, but it seems to have stopped leaking and kind of dried up. My best guess at this point is that the thermostat housing is leaking, and when it pools up in the valley, it picks up dirt that has accumulated down there, and ends up looking like oil. For sure, the thermostat housing is seeping coolant, so I'm going to order up an aluminum replacement and see if that cures the issue. I'll post a follow up with results, because it annoys the heck out of me when I find somebody with the same problem, but they don't follow up with a solution.
I dug into it a little today. Went to order the aluminum housing, the good one, and it's out of stock. Didn't want to screw around with the chineese aluminum ones on ebay, and not being able to wait, I went down to O'Rielly Auto and bought a Dorman replacement with lifetime warranty. Nice thing there is that I'm in a national database, so if it fails away from home, I get a new one for free at any store.
Now on to the project. Pulled the T-stat housing, it's definitely in need of replacement, but the valley is definitely filled with oil too. Don't know what that sensor is in the middle of the valley, but it sure looks like the source of the leak. There's clearly been a mouse or something spending some time in there, because there's all sorts of acorn shells and whatnot....now soaked with oil. Thinking I might pull the intake and really clean it up under there. Pull whatever that sensor is, and see if there's an o-ring or something to replace on it.
hmmm, I dug some of that muck out of there, and it doesn't smell like oil at all. Maybe just decomposed leaves, mouse ****, and yellow anti-freeze mixed together into a goo that looks like oil? I guess that's a knock sensor there, attached with a bolt in a blind hole, so not an oil leak source as far as I can tell. Definitely no oil coming down from the valve covers. Think I'm just going to clean it up the best I can without removing the intake, put it all back together with the new T-stat housing, and see how it goes.
Final update: No runs, no drips, no errors. Cleaned out all the gunk in the valley as best I could, replaced the thermostat housing, topped off the coolant. The car has been driven several times now, and there are no leaks. The valley has dried out, and there aren't any signs of anything that looks like oil, so it must have just been coolant mixed with dirt. Strangely, the car seems to run better when cold and warms up faster, and the heat is available sooner, maybe because it's not perpetually low on coolant I guess.
That plug looking thing at the rear of the valley is the oil pump drive gear, and it does have an o-ring seal that could leak oil, but I don't see any evidence of that at this time.
It would have been nice to get the one piece aluminum housing in there so I didn't have to worry about it anymore, but I guess I'm married to O'riellys on this deal now. Hopefully Dorman did something to improve the part vs. just cloning it.
Glad to hear you got everything sorted out. The life span of the housing is just luck of the draw. I had one that lasted over 150,000 miles while others have replaced them more than once in 30,000 miles.
02-03-2019, 10:25 AM
Oil leak - 4.0L upper rear?
