Coolant leak from rear of 5.0L engine | Ford Explorer Forums - Serious Explorations

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Coolant leak from rear of 5.0L engine


Explorer Addict
December 5, 2010
Reaction score
City, State
Seattle WA
Year, Model & Trim Level
98 Limited V8 AWD
Howdy! A rookie on this site, but no stranger to other Ford repair forums; received and (hopefully) also delivered some good advice over the years.

Today I need a hint about a small coolant leak on my 98 Limited with 5.0L engine. Tolerated it for a while, and finally decided to find out the source. After pressurizing the system I can see the coolant dripping from the transmission bellhousing. Looking inside, the source appears to be behind the flex plate, possibly on the driver side. As far as I could see (and stick my hand), the rear surfaces of the intake manifold and of the cylinder heads are perfectly dry. I don't see or smell any coolant in the oil. This leaves me with a choice between a crack in the engine block, or the lesser evil of a corroded freeze plug. Are there any freeze plugs at the back of this engine, under the flex plate? Is this common on the 5.0L? It has about 140K miles, but the engine is otherwise in perfect shape, never overheated and the coolant has been well maintained. I can probably pull out the engine myself, but if removing the transmission is the better option, I would need to take it to a mechanic. Any opinion on that? Thanks a bunch!!!

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Welcome to the site!

I know you probably already did, but have you checked under the thermostat housing on the front top of the engine block? Fluids take some odd paths down and around the engine. I mention it because that's a common coolant leak.

Also, it appears there is a freeze/core plug on the top left rear of the engine block. If you look closely in the last picture of this post you can see it: Link

The transmission shouldn't have any coolant in it. ATF circulates to an external cooler for that job.

Thanks for the tips, OneLever! Sadly, it's not the thermostat housing - perfectly dry underneath.
Had fun looking at the pictures of the project in progress too. The freeze plug that's visible in the last photograph is at the back of the cylinder head, not the engine block. Incidentally, this one is perfect dry in my case... What I am trying to figure out is whether there is one in the rear of the block itself -- which would have been covered by the transmission bellhousing in that photo.
And yes, I am aware that there is no coolant circulating through the transmission. Where I see seeping from is the bottom of the bellhousing, and it almost certainly gets there by flowing along the rear of the engine, behind the flexplate.

Ah, I understand now. Did some searching and couldn't find any rear shots with transmission off. Might help looking through the Explorer Photo Gallery but nothing's tagged...

I just thought of something. Does your 4R70W have a plastic plug on the bottom of the bell housing to access the torque converter drain plug? On mine I can just pop it off and look around the bell housing. With a flash light and some goggles (antifreeze will blind you...) I could look at the rear of the engine block for freeze plugs. I know they removed that plug at some point though.

If that fails I'd search for threads on torque converter replacements.

No freeze plugs there

Here's a photo of a 5.0L out of a Crown Victoria. As you can see there are no freeze plugs in the rear of the block.

I believe the plug in the rear of the passenger side head is prone to leak.

Thank you for that photo 2000StreetRod I've been wanting a shot of the 5.0L from that angle.

Edit: Is the upper intake manifold inlet on that engine opposite of the explorers? It looks like it comes from the driver's side on there.

Thanks a lot for that shot and the advice, 2000StreetRod. Both freeze plugs at the rear of the heads are dry in my case, and I can't see anything leaking along the top of the engine, so it must be coming from under the flywheel. In your shot I see two bolts with square heads, just above the camshaft. Would those be coolant passage plugs?

To OneLever: yes, it has the bell housing plug. But you can't see the rear of the engine from there - the flex plate is in the way.

eBay photo

Thank you for that photo 2000StreetRod I've been wanting a shot of the 5.0L from that angle.

Edit: Is the upper intake manifold inlet on that engine opposite of the explorers? It looks like it comes from the driver's side on there.

I don't know for sure because I grabbed the photo from eBay. The upper intake manifold looks similar to the one used on the early F-150 Lightning with a driver side main air inlet tube.

oil galley plugs

Thanks a lot for that shot and the advice, 2000StreetRod. Both freeze plugs at the rear of the heads are dry in my case, and I can't see anything leaking along the top of the engine, so it must be coming from under the flywheel. In your shot I see two bolts with square heads, just above the camshaft. Would those be coolant passage plugs?

I believe those are threaded oil galley plugs. There are supposed to be three in the bellhousing (all threaded) and three behind the timing chain in the front (2 press in and 1 screw in).

It's the timing cover - any tricks to remove with the engine in place?

OneLever was right: fluids do take strange paths! It's dripping off the rear, but I finally found the source and it's at the front of the engine. The coolant seeps out of the top of the timing cover seal. I will take the water pump out and try to tighten the timing cover bolts, but it's almost certainly a losing proposition, and the timing cover gasket will need to be replaced. The timing cover bolts to the oil pan, and that means pulling the engine out to do it. Or does it? I owned a couple cars with the 3.8L, for which the books said to drop the pan, and only after the fact I learned of a mechanic's trick to wiggle the timing cover out with the pan in place. Hopefully someone knows of a similar trick for the 5.0L.

Well you're halfway there! All that you need to do now is some grunt work. I had heard of the timing cover leaking but thought "there's no way that applies to him..." Lesson learned. Please keep us updated.

Replace water pump too?

Finished the disassembly, scraped off the rock-hard gasket, replaced the timing gears and chain, and ready to re-install the front cover. But before I continue, would like to hear your opinion on replacing the water pump. I can't see anything wrong with it: the bearing is solid, the impeller is solid, and there is no leak. Iit's the original pump with 137,000 miles and I am wondering how much more I can expect from it. In the not-so-good old days one was lucky to have them last even 50,000 miles. Obviously, with better centered fan, controlled belt tension and improved coolant, they are lasting longer. So save the $75 and take the risk or play it safe? What would you do?

If the water pump is original with 137k miles on it I would absolutely replace it. There's no way of knowing how much longer it will last and you're already there with everything apart. Now is not the time to be cheap about it, save yourself a lot of work later on and just put a new pump in now.

I have about 163,000 miles on what I believe is the stock water pump. I don't really know the failure rate of them on the 5.0L's. I would at least replace the small bypass hose since it goes often and is hard to reach.

Did you take a picture of the leaking area?

Unfortunately, no photos

The failed front cover gasket was apparently around the driver side coolant passage. Couldn't see the actual spot from which it was leaking, but most likely it was at the top, because when pressurized, a puddle formed just behind the cover there. As many have found before, the studs around both coolant passages were rusted, which confirms the diagnosis. The gaskets on both sides of the timing cover were hard as a rock and extremely difficult to scrape off, even after liberally brushing them with remover fluid- never encountered anything like that.

Couldn't take any pictures; the spot where it was puddling is so well hidden that I could barely even peek in there with a mirror -- which explains why I didn't supect the front cover gasket to begin with. A bit of the coolant went straight down onto the stabilizer bar, but most flowed on top of the oil pan lip and dripped from behind the flexplate. All that with a pressurized cold engine, of course; otherwise it just evaporated into thin air.

Still contemplating the water pump replacement. If I do, it will be a pricey Motorcraft, because in the past I had very bad experience with aftermarket pumps.

Now to the challenge of reassembly. Not sure yet how to deal with holding the crankshaft to torque pulley bolt. It was a breeze on the way out, because I removed the radiator and used an impact wrench, but would rather not bang that bolt back in with it. We'll see...

Oddly, this vehicle does not have a water-cooled oil filter adapter. Must have been some late production economy, because the FSM clearly shows it.

And thanks for the tip about replacing the bypass hose! I am on my way to Napa to get one.

I haven't had to deal with many gaskets on my V8 yet, but the ones I did were rock hard. Had to use a plastic scraper and if that failed very precise lateral force with a flathead screwdriver so as not to scratch the surface.

Look at the price of the motorcraft water pump on if you decide to get one. They seem to have the best prices for OEM parts. I don't know enough to tell you whether to replace it or not.

Glad to see you're making progress.

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Timing Cover Job

As I found out, the leak was from the timing cover. Here is the conclusion of my experience, with some details that may be helpful to other brave souls tackling this challenge.

1) The first step is, of course, removing the serpentine belt. The gap between the fan and the radiator is too narrow for a breaker bar, so the special tool is the way to go. I have the fancier two-piece ratcheting one, which makes this job a breeze. If you are using the simpler one-piece, it's probably easier to access the tensioner from underneath.
2) I heard of improvisations to remove the fan, but you really need the slim 36mm wrench for the hub nut and the 72mm holder for the pulley bolts. Except for the insanely pricey OTC products, I could not find those sold invidually anywhere. The universal kit that O'Reilly rents in this neck of the woods does not include these sizes either. Ended buying a 10-piece set, which is sold under several different names. I got it from Tool King as 'Performance Tool Model W89400'. Anyone interested in buying the extra 8 fan wrenches that I don't need?
3) The FSM (Ford Service Manual) instructs to use a 'suitable' strap wrench to hold the harmonic balancer while removing the center bolt. I have yet to find a strap wrench that will hold 150 ft-lbs of torque - or even 50 ft-lbs for that matter. The easy way is to use a pneumatic impact wrench, so that's what I decided to do. Unless you have a very short one, there is not enough clearance, and the radiator has to come out. On this vehicle the radiator is tightly sandwiched to the A/C condenser, so you need to separate them.
First you undo the two bottom clips, one on each side, then move the condenser horizontally to the passenger side until the two slides on the driver side clear. Easier said than done! The larger of those bottom clips, on the passenger side, which looks like an oversized backpack buckle, is about 3" long. You need to pull the radiator that much apart from the condenser on this side, while the driver side is still engaged in those horizontal slides. There is no good way to gain leverage without damaging anything and it feels and sounds like something will break. Some reported chopping off that buckle, out of frustration. I later found out that if you first take the radiator off its passenger side support, this maneuver is a bit easier. When reassembling, notice that there are two horizontal slides on the driver side: one at the top and one about halfway down. Both must be engaged at the same time.
4) To reinstall the balancer I did not want to bang the bolt with my impact wrench to an unknown (and probably grossly excessive) torque. Harbor Freight sells a very simple pulley holding tool called 'Pittsburg 66385' for $10. It's an 13" bar with a curved foot and a sliding round pin. The foot goes on the inside of the pulley, and you adjust the pin to grab the outside. To avoid damage to the grooves, I put the serpentine belt back on, which provided a cushion (and increased the friction). The bar is way too short to hold by hand, but just long enough to support the end on the frame.
5) The 5/16" (coarse) bolts and studs that hold both the water pump and the timing cover are all non-standard lengths, which you can't buy anywhere. I reused some, but the ones around the coolant passages were rusted from the leak. Nothing bolts to the studs - they are used just for attaching wire harnesses, to keep those from getting tangled in the belt. I replaced them with regular bolts. To attach the harnesses, I put large ('fender') washers, in which I drilled a couple small holes, then just tied things with copper wire. The bolts that I used were the nearest 1/2" length up, so they had to be cut to size. To have enough threads after cutting, I extended them by about 1/4" with a die. Full-threaded bolts might have been a simpler solution.
6) On a previous job, on the 3.8L V6, I had to chop the timing cover, because the bolt next to the coolant passages welded itself the aluminum after rusting. After discussing the subject with my mechanical engineer friend, I decided to coat those with a sealant. Hopefully, this will help.
7) At 137K miles the timing chain was definitely stretched. I replaced it, together with the two gears, with Motorcraft parts. Twice as expensive as aftermarket, but hopefully, more reliable. The water pump still looked good, but I followed the 'better safe than sorry' advice given to me here and replaced it too; again, with Motorcraft.
8) The Felpro gasket kit comes with two pieces of cork. The included instructions tell you to cut the existing pan gasket flush with the block, then use those. Obviously, this was written with the old-style cork gasket in mind. This engine has a steel-backed gasket, which I carefully separated from the timing cover with a putty knife before disassembly. All that was needed to put things back together was some black silicone to fill the gaps.
9) It's virtually impossible to see what's happening on the upper driver side of the timing cover when reinstalling, because that corner is hidden behind the bulky accessory bracket. That's where I ended up trapping the oil pressure sender harness under the timing cover and wondering why it won't go in all the way. It should have been unplugged from the sensor and taken out of the way. Same for the crankshaft position sensor harness on the opposite side. It's best to take off the two bolts and move this harness away with the sensor attached.
10) As others reported, junk falls into the pan while scraping the old gasket off. I stuffed a rag in there to catch it. Luckily, the coolant did not leak into the pan at all because I drained the system before taking the radiator off. Nevertheless, to be on the safe side, I changed the oil at the end of the job.