2002 Expo cooling system boiling and OD OFF light flashing

[Scurvy]

I am having some issues with my 02 Expo, 4.0L v6. First, some background.

I bought it last April (so ~16 months ago) and it had a thermostat housing leak. Not a big one, so I didn't get around to fixing it until a few months ago. In that time I drove the truck thousands of KM without an issue, topping up the coolant every week or two. I'm pretty sure my thermostat was also fked as the temp gauge would usually sit about halfway between cold and normal.

Since replacing the tstat housing and tstat I have pulled my tent trailer a few hundred km without issue along a combination of city, highway, and gravel roads, in addition to daily driving and an overnight hunting trip without the trailer. In this time, my temp gauge continued to read between cold and normal.

Last week I went hunting again. I was doing a good pace up a gravel road and heard an odd noise from under the hood. When I pulled over and checked my coolant reservoir was full to the top and boiling! I let it cool down, the coolant level in the reservoir came down a lot, almost to empty. I filled it up, let the truck idle for a bit, squeezed the top and bottom radiator hoses to try and burp the system. Everything seemed to be fine, so I kept going. At no point did my temp gauge go above normal.

Fast forward a bit, I'm now going up a big hill for a few km. All the sudden I get DING DING DING, my O/D OFF light starts flashing, and I lose power to the wheels. I pulled over, let things cool off for a while, fire it back up and everything seems good to go. Again, my temp gauge never went to normal, let alone above it.

After I'm done hunting for the day, I get back in the truck and head home. I get halfway off the gravel and my OD OFF light starts flashing again. Didn't loose power to the wheels or anything, still had overdrive, no difference in the way the truck was running. Pulled over, waited a bit, started driving again. Get just off the gravel, and my OD OFF light starts flashing again. Pull over. Wait a bit. This time my OD off light came on only a minute or two after starting to drive again (going ~80km/hr), and I said **** it I'm driving home unless this stops me. Drove home fine without any real issues.

I have since driven the truck around town a few times (don't go out much due to Covid these days) since then and haven't had the light come on or noticed any serious issues. However, my wife pointed out I have a small coolant leak now. Kinda looks like its coming from the water pump, but I'm not sure.

SO! With all this info, what might be my issue(s), and what might be my fixes?

 

[Rick]

I would start by plugging a scanner into the OBDII to see if it has stored any codes.

 

[Scurvy]

I would start by plugging a scanner into the OBDII to see if it has stored any codes.

Good call. Interestingly, I DID have a check engine light on for the longest time (p0128, coolant not getting hot enough fast enough) which actually went OFF for the first time in a long time the same day I had the troubles. It is still running below normal operating temps.

No check engine or OD OFF lights are on right now, but shes throwing two codes. P0128 which its been throwing forever, and P0133 which is a new one and is an 02 sensor issue.

Im going to clear the codes and check it again after I go out next.

 

[Scurvy]

Nobody has any ideas? I don't want to take it into a shop until I at least have an idea of what might be wrong.

Edit to add that I do have heat - hot air blows out the vents just fine. Top radiator hose gets hot to the touch after its ran for a while too.

 

[Josef161]

I have read here that the water pump starts to leak coolant if it is on its way out (that's my best guess, you could do some research on it. It would explain why your coolant starts to boil).

Other then the water pump it could be a blown head gasket (but i guess that you would have mentioned if your coolant smells like gasoline or engine oil).

Keep us updated

 

[Scurvy]

So I took it to the shop for a flush and fill. They called me to pick it up, went to get it, and there was a puddle under it. Apparently it wasn't leaking when they pressure tested it, but it leaks without pressure if its hot.

Replaced the water pump, which had a shot bushing and was well on its way out. Fixed that leak.

Now I've got a new leak, this time it looks like it might be coming from the thermostat housing, specifically from the bottom side where it bolts down to the engine or whatever is below it. The drip is coming from the back of the engine but I think its running along the valve cover on the drivers side and then dripping from the back end of the valve cover.

It wasn't leaking Tuesday afternoon when I picked up the truck, and it wasn't leaking Tuesday evening after a good rip in the truck, but mid-day wednesday there was a puddle under it, so I put a container under it. I've gotten maybe a cup of coolant in the container at this point, some ~15 hours later.

 

[donalds]

4.0 SOHC Metal Thermostat Housing Comparison

I obtained 2 thermostat housings for my 2001 Ranger. The original is plastic and not leaking yet but you know how that goes on the 4.0 SOHC. The first one is from Simmons Autosports. I have used theirs before and its a great part, way better than the original plastic one from Ford. Here are...

www.explorerforum.com

 

[Scurvy]

4.0 SOHC Metal Thermostat Housing Comparison

I obtained 2 thermostat housings for my 2001 Ranger. The original is plastic and not leaking yet but you know how that goes on the 4.0 SOHC. The first one is from Simmons Autosports. I have used theirs before and its a great part, way better than the original plastic one from Ford. Here are...

www.explorerforum.com

It wasn't leaking at the Tstat housing before this. Do you know if the Tstat housing has to come off to do the waterpump? I feel like yes it does, but i"m not certain?

 

[donalds]

I don't think so but I'd put a metal one on anyway

 

[Scurvy]

Looks to be leaking from the middle bolt on the tstat housing. I checked the bolt and its tight. Any suggestions on how to fix this?

 

[Josef161]

Looks to be leaking from the middle bolt on the tstat housing. I checked the bolt and its tight. Any suggestions on how to fix this?

View attachment 318288

Check the other bolts how they get sealed (maybe the mechanic lost a washer or something else) otherwise you could try an o-ring. If the housing is cracked i fixed mine with soldering the plastic, clean it really good (als use sand paper) and then i put some jb weld epoxy on it. I did the epoxy fix one year ago and it still doesn't leak at all. Btw the water leak could also be coming from the sensor, i know for sure that there are 1 or 2 o-rings in there, maybe the mechanic lost it...

 

[Scurvy]

Check the other bolts how they get sealed (maybe the mechanic lost a washer or something else) otherwise you could try an o-ring. If the housing is cracked i fixed mine with soldering the plastic, clean it really good (als use sand paper) and then i put some jb weld epoxy on it. I did the epoxy fix one year ago and it still doesn't leak at all. Btw the water leak could also be coming from the sensor, i know for sure that there are 1 or 2 o-rings in there, maybe the mechanic lost it...

Its definitely coming from under the bolt. With the car running you can see the water slowly oozing up from around the bolthead. Looking at a picture online, it would appear that bolt shouldn't be coming in contact with coolant at all, which means the thermostat housing must be buggered and leaking internally...?

I'm not going to bother with trying to fix this housing. It was bought used in the first place, and didn't leak until now (but the coolant system did get pressure tested twice in this week) so I'm just going to replace it. Already ordered a replacement from RockAuto.

If this just causes another problem somewhere else in the cooling system I'm going to be pretty damn pissed off...