Coolant leak on 2002 Explorer XLT V6 4.0L SOHC

Hi there, new to the forum but have been lurking a bit.

My wife has a 2002 Explorer XLT V6 4.0L SOHC with about 100K miles. There is a coolant leak that I cannot find the source of. I have changed out the thermostat, water pump (and gasket), and the upper and lower radiator hoses. It still leaks.

I have checked the engine oil and it appears okay. The Explorer does not emit any white smoke.

I can't really tell where the coolant leak is coming from, but it appears to start somewhere up and behind the water pump - the alternator is in the way. The coolant runs down the front passenger side of the engine and falls on/behind the front cross member.

It is a pretty steady leak. It only leaks when the engine is running. When the engine is off I can fill the reservoir without it leaking (as far as I can tell). I have run the heater successfully and have confirmed that the thermostat is working correctly (upper radiator hose gets hot). I have not done a coolant system pressure check yet.

Some of the other posts point to possible issues with either the timing chain cover gasket or the upper/lower intake manifold gasket. How difficult are these jobs to do for someone with intermediate skill? How expensive (roughly) would this job be if I took it to the dealer or a repair shop?

Any tips/ideas/suggestions would be welcome.

Thanks in advance,

Dwight...

sounds like a lower intake coolant passage is leaking. its not easy or very hard its time consuming to get everything off, to get to the bolts to remove the the lower intake.

thanks 2003vstrom.

I was surfing around and found this http://bengrosser.com/howto/fordthermostat and noted many similarities to my situation with respect to the lower thermostat housing and the coolant splatter.

The lower thermostat housing on my wife's Explorer looks pretty beat with gummy coolant colored residue around it...I think it might be possible that it's leaking at the rear of the housing. I'll have to try gunning the engine while watching the area to see if anything spews out. When the engine is idling there's a pretty constant stream of coolant.

I'm thinking of replacing the lower thermostat housing first.

Uh oh!

I replaced out the lower thermostat housing; the old one definitely appears to be the problem...it was totally corroded and it looked like there was a pinhole near the back bolt area.

However, I couldn't find a replacement coolant temperature sensor and tried using the old one. When I buttoned everything back up and started it up it ran really rough. Could this be caused by a faulty coolant temperature sensor? I tried to run it for a while - probably no more than five minutes total - but it really does run rough...almost like I'm missing a spark plug or something. I'm afraid to try starting it up again and having it lock up the pistons and freeze the engine.

If I replace the coolant temperature sensor will this problem go away? Need to know as soon as possible so I can decide what to do next.

Not knowing what all you removed to do the work, My guess is you left a sensor or a hose disconnected. Go back over everything you unplugged or disconnected, and be certain you got re attached. When digging into an engine, there are usually lots of things to disconnect, and it's easy to miss one when putting everthing back together.

Thanks FordLover,

Basically I did the following to replace the lower thermostat housing:

1) drained radiator
2) removed fan shroud
3) removed upper radiator hose
4) removed upper thermostat housing and thermostat & o-ring
5) unplugged the harness going to the coil to make room to remove the lower thermostat housing
6) removed the heater hose going to the lower thermostat housing
7) unplugged the coolant temperature sensor harness
8) removed the coolant temperature sensor
9) removed the lower thermostat housing

Cleaned up the area around the intake/block. Installation was the reverse.

This morning I went and got a new coolant temperature sensor and installed that. I also verified that everything was plugged back in where it was supposed to go.

I started it up and it ran a little ragged; dying out a couple of times. I figured that was a big improvement over last night's really rough idle. It took a lot longer -- it seemed -- for the Explorer to get up to temperature. Per my Haynes book I left the coolant reservoir cap off while letting her get up to temp. I verified that the upper radiator hose got hot.

Right now I'm waiting for it to cool off then will check the coolant level and put the cap back on. Then I'll run it with the heater on max.

I noticed that running it last night with the old temperature sensor (which must have been faulty) caused the service light to go on.

Whew!

Alright. It appears that everything is running good now. The idle has settled down and it doesn't stall when I'm stopped. Of course, it could be because everything's warmed up. I'm going to drive the Explorer to work (about 12 miles one way) and will check everything out.

i am having this same problem with my new explorer, from what i can tell its the lower intake gasket.

Hi specialized7,

It took me a while to figure out that the lower thermostat housing was the problem. I'll post some pictures later on. The old housing was pretty messed up.

Take a look around the thermostat housing and intake. That area should be relatively clean. Mine was covered with crud and I could see seepage when I added new coolant to the recovery tank.

This was enough excitement for me. I've driven the Explorer to work and had no issues. Verified no leaks when I got here. The real test will be when I start it up this afternoon after its been sitting for a couple of hours.

This is mine:
From what I see, when they made the housing, they did it in layers or something. Mine is leaking thru one of those. Its not bad, but you can definitely smell coolant when driving.
I bought a new lower housing, t-stat, sensor and the housing O-ring. Still have to get a t-stat o-ring, but more or less, it looks like a fairly easy thing to swap out.

Hi clarks2001,

I did a double-take when I saw your picture...my old housing looked exactly like that. I had a pinhole on the back side (towards the firewall) and that was the source of the leak.

The removal and install went pretty smoothly. Take a look at that link I posted earlier; he makes some good points about the three tabs on the bottom of the lower thermostat housing. When I took my old one off those tabs were long gone.

Here's a pic of the housing.

This is a close up of the sludge:

This is what the top of the manifold looked like when I removed the lower housing:

Here's a shot of the lower housing; you can sort of tell where the failure is/was by the amount of crap:

holy crap. mine isnt that bad lol. mine just kinda fizzles up at the top. it gets no worse than the pic i posted shows. But still, I am gonna get it replaced...probably in 400 miles when I hit 100k. Gonna get the plugs done too and probably fuel filter. hooray 100k mile mark. Guess things will really start breaking for me now haha

Here's the parts list and prices for the thermostat housing repair. All these parts were picked up at my local automotive distributor "Aloha Automotive Distributing" on 98-790 Moanalua Rd Aiea HI 96701, phone (808) 488-6868. They had some good discounts; saved about $40.00 off list for the thermostat housing.

• coolant temperature sensor = Motorcraft P/N DY1004 = Ford P/N 3L8Z12A648BA = $25.19
• lower thermostat housing = Motorcraft P/N RH148 = Ford P/N 2L2Z8592BA = $40.80
• lower thermostat housing o-ring = Motorcraft P/N RG614 = Ford P/N 1L2Z8255AA = $3.95

The following lists the parts & prices for the thermostat and water pump replacement. I replaced all the hoses and serpentine belt as well, just because. I got all this from the local Checker Auto Parts.

• re-manufactured water pump w/gasket = $49.99
• accessory/serpentine belt = $6.29
• upper radiator hose = $22.99
• lower radiator hose = $16.99
• Ford fan clutch tool (loaner was already loaned out) = $29.99
• bypass hose = $6.29
• thermostat = $15.99
• thermostat o-ring = $1.49
• gallon coolant = $14.99

Too right clarks2001! I think Ford used all these plastic parts just so they would crap out when you hit 100K. "Planned Obsolescence" as they call it.

Here's another tip. Be careful with the radiator drain petcock. I snapped the end off of mine. Luckily the inside was hex shaped.

I seem to be having the same issue with my 2005 Mountaineer. I know the leak is coming from the housing, but not sure If I should replace both the top and bottom at the same time? How hard is it to replace the housings? Should I also replace the CTS as well?

Hi nickorsi,

I recommend changing the lower thermostat housing only. The top, at least on mine, appeared to be in excellent shape.

It might be optimal to change the coolant temperature sensor at the same time. I tried to reuse the old one and that didn't work too well for me (I must have tweaked it somehow)...but you might have better luck. At the minimum, if you're not going to change the sensor, change its o-ring. My old o-ring was flat -- it should look like a fat doughnut.

The replacement of the housing wasn't too bad. Check that link I posted earlier, he makes a very good point about the lower thermostat housing having three tabs that held align the housing within the manifold. I did it in about an hour or two. You'll need to have a torque wrench that can do inch pounds, 8mm socket (I believe that's correct), and maybe a flex socket to reach the back bolt. Be very careful taking the old housing out -- be sure to pull up (about an inch) and then forward...that way you don't break the tabs.

Good luck!

If you're removing the lower thermostat housing you may as well check the bypass hose at the same time. You might as well change the thermostat too.