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External Oil Leak from Head?


Active Member
October 16, 2015
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City, State
Ringgold, Georgia
Year, Model & Trim Level
1998 Ford Explorer XL 4WD
Hey guys. To start I've guy a 98 OHV that's leaking a good amount of oil. Constant drip at running pretty much. Dripping from the mating between Engine and Transmission. I had believed it was all from the Rear main and replaced that months ago (horrible job to do alone). That helped the leak a bit. I cleaned the engine to see where the oil was coming from and it appeared to be running down from behind the intake and down both sides of the block and dripping from the mating area at the bottom. I could see the oil running down. Figured it was the Intake valley because I had a slightly rough idle at times and my valve covers didn't appear to be leaking. Replaced the lower intake gasket and put healthy amount of RTV at the ends and let it cure for 24 hours before running the engine. Still leaks and seems to have gotten worse than before rear main seal replacement. I cleaned the engine again and started it just long enough to get drops of the bottom and started feeling around for oil. Valve covers looked and felt dry. RTV mushroomed out of the intake was dry. But I felt oil at the head to block mating surface. Clean oil so I know it's was fresh. Is it possible to leak oil externally from the back of the head? Coolant and oil is not mixed. I plan to pull plugs and look at them when the rain finally stops. I also plan to use baby powder to try and confirm the oil leak location. If that didn't work I'll buy some UV dye and maybe pull the starter to look for oil on the flywheel. Just looking for some insight. I know external head leaks aren't common and that it's usually the intake or valve covers. All I know for sure is I need to get this leak fixed and I've got oil on the top of the block making it to the bottom. Any ideas or help would be appreciated.

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Is it toward the passenger side? I wonder if the camshaft sensor is leaking.

edit. could there be an oil plug on rear of cylinder head?

I found this thread


I thought about it possibly being the camshaft sensor but didn't think this amount of oil could possible come from there. It is possible that that's leaking but the head mating surface is a touch higher than the can sensor. I'm not sure if there's and oil expansion plug. Hmmm. I think there's a plug above the rear main but that's still surrounded by the bell housing. Oil seemed to run down both sides.


Make witness marks/ alignment marks on where your hood hinges mate to the underside of your hood.

Remove the 2 hood bolts on each side, and remove the hood .

Even though the hood is aluminum, and only weighs 30 pounds, it's bulky and best done with 2 people so you don't damage it.

Get on top of your engine, and at the rear of the engine, clean the pad area where the cam synchro mates to the block as best as you can.

Clean the areas where your heads meet up with the block.

Get underneath, and clean off the oil dripping down the block on both sides.

OK - now your two main target areas are clean ;)

When done, leave the hood off, and drive around the neighborhood for a few miles.

Return home, get back up on top, and inspect the areas you cleaned.

A good mechanic lighted inspection mirror helps -

LINK: General Tools Telescoping LED Lighted Inspection Mirror, 360-Degree Swivel for Extra-Viewing-80560 - The Home Depot


Unfortunately I think it's still the rear main seal. It could be the oil pan gasket or plug on the back of the block, but it's certainly inside of the transmission bellhousing. Which is not good news for me because I'd rather pull the heads than the transmission. I'll have to pull the starter and look in there after the engine cools down again. I'll be disappointed if it's the rear main seal again because I used the proper Motorcraft seal, repair sleeve, and the 90 dollar OTC as well. I'm guessing any top end oil I found was leftover from the intake gasket change because this was the only powder disturbed other than a very minor front seal seep.



Question - because what you've written it isn't really clear to me :)

Door #1: Did you replace the leaking rear main seal with the FORD branded 4.0 Ohv Rear Main Seal Repair Kit (Made in Germany) that you buy over the parts counter at the FORD dealership for approximately $60 - $70


Door #2:
Did you buy a new Motorcraft brand rear main seal and then added an Aftermarket metal crankshaft repair sleeve?

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I had ordered the Ford part number you shared off of Amazon. I had thought it was Motorcraft but looking back at my orders it was a Ford product and came with the Repair sleeve.

Screenshot_20210923-152231_Amazon Shopping.jpg


Did you perform Step #2 of the Installation Instructions?

Ford TSB.jpg

Yes. I actually used that image from the forum as my guidelines. I noticed some minor scratches on the crankshaft that I must have inflicted removing the old seal but I used an emery cloth and took off the edges. Figured the repair sleeve would cover plenty of good metal to seal.


To clarify, did you oil the sleeve surface where it meets up/ interfaces with the rubber seal surface?

Because if you didn't, you ran the new rubber seal dry...

The aggressive/rough contact surface/interface of the metal repair sleeve will ruin the new rubber main seal within a few revolutions of the crankshaft.


To clarify, did you oil the sleeve surface where it meets up/ interfaces with the rubber seal surface?

Because if you didn't, you ran the new rubber seal dry...

The aggressive/rough contact surface/interface of the metal repair sleeve will ruin the new rubber main seal within a few revolutions of the crankshaft.
I oiled the seal to sleeve surface and the seal to block surface. I left sleeve to crank dry. I used new 5w-30 oil for the oiling.


OK - hopefully your leak is somewhere else :)

By chance that you do have to do this again, here's an old school trick / tip.

To help / increase your chances of success, pack the rear/backside of the rubber seal (where the coil spring is)
with standard grease (Post 6, Picture 3).

This does two things, the first is that it prevents the spring from moving, misaligning, jumping off when installing.

Second, it adds some additional compression/pressure on the rubber seal so that it mates up quickly with surface of the metal sleeve.

I'm thinking I'll but an inspection camera to help me see inside the bell housing. I'm hoping it's not the rear main still but I guess I'll just have to see. Packing the seal with grease certainly makes sense and if I have to remove it again I'll definitely do exactly that.

Well after buying and waiting for an Endoscope to arrive I removed the starter and tried to see what little I could issue the bellhousing. It looked like there was oil glistening inside on the back of the block and around the main seal area. None on the fly wheel though. So I'm guessing it is the rear main leaking still or something above it. As much as I didn't want to do this job ago, I'm willing too to stop the leak. So now I'm looking for tips on what's the best seal, repair sleeve, techniques, anything to get a leak free rear main. I think I'll also attempt to change the oil pan gasket when the transmission is out this time. So tips on that would be appreciated as well (I'm 4wd). Or should I just try running a heavier weight oil or switch back to conventional oils. I just want leak free so my fiance stops trying to get me to sell the X haha

I don't have any suggestions / tips on that job....but when the trans is off again replace the freeze plugs at back there....AND the cam sychronizer/sensor assembly ...it's a headache on our 4.0 ohv's but having the trans out and doing it from under / behind should be relatively easy versus the standard way of pulling upper intake etc.


I'll have to look into the process of installing and removing freeze plugs. I'll look into the cam synchro although I'm not sure on the alignment process involved in that.

Also I'm curious if I need to pull the Ford repair sleeve I installed off and install the new sleeve I received? I assume that's the process. Needing tips to get the pressed sleeve off if that's the case.

Okay I've got the transmission pulled again and after looking at the UV Dye it's certain that the oil pan is leaking. I'm not certain the rear main is though. Around the outer edges of the rear main does like up, but I put Sealent around the edge on the outside and it's proven to light up under uv so without seeing oil coming from the seal in not sure. I'm not certain the oil pan would leak much during operation. So I'm trying to decide if I should remove my ford seal and sleeve and replace it with a felpro or ford set. If the rear main was leaking considerably would you expect to see UV oil on the flywheel? Or slung around all around the housing? I saw no oil on the flywheel and all oil I did see was on the lower half of the engine mounting plate. Nothing above the oil pan that I could tell. If I remove the rear main seal, how do I remove the repair sleeve? Do we know for a fact that the Ford seal is rubber and needs to be lubricated? I'm still just really wanting a leak free install.

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If Picture #3 (Non-UV Picture) was taken the moment you removed the flexplate, and you did not wipe anything down before taking it, looking at that pic highly magnified in a new tab, I believe your problem is with the oil pan seal.

So, if I were you, I'd leave the main seal alone.

I also have a lot of time with this engine - 16 years as a Daily Driver - and I will offer up the following based on what I've experienced.

This V-6 engine vibrates quite a bit more than a Chevy/Ford OHV V8.

The oil pan is cast Aluminum- which is another way to say it weighs a lot.

The OEM German pan gasket (the ONLY gasket you should ever consider) is rubber molded over a steel core.

The majority of the bolts holding the oil pan to the block are - I believe from memory - M6 (meaning small diameter). The same size ad the bolts holding down the valve covers...

Between the vibration and the heat cycles, every 2-3 years, I found that I had to slide under and tighten up all of the accessible oil pan gasket bolts.

This effectively helped slow down any weeping I had from the pan gasket for 2 years or so...

Now - If I was as adventurous as you, and did remove the oil pan from the engine (while it was in the ex) here's what I would do to hopefully keep from ever having to go through this exercise again.

Where I could, I'd change over from M6 bolts to M6 studs in the block (with Loctite on the studs where it goes in the block), and then would button it down with ny-lock flange nuts.

After 14 years, that's what I finally did topside with the valve covers. I bought M6 all-thread lengths and cut and sunk studs in the heads (with Loctite applied) and held it down with ny-lock flange nuts.

Here's a good distributor of metric fasteners so as to get an idea of what's out there: Metric Hardware, Metric Fasteners, Metric Bolts, Metric Nuts & Time-Sert Thread Repair

BTW - Is your Ex 4wd or 2wd, Auto or 5 Speed Manual?

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It's 4wd with the Auto 5r55e. That non UV picture i believe is before wiping off some of the sludge that was on the back of the pan. I currently only have the metal and rubber Fel Pro oil pan gasket on hand. I'm guessing these do not work well?