very Intermittent overheating

[abcducati]

So my 2004 XLS 4.0 overheated back in late March/early April, and turned out the water pump was bad. I replaced the water pump, fan clutch and thermostat at that time, and everything was fine until about a month later in early May when it suddenly overheated when my wife was driving the truck home. She pulled it over and when I got to her location there was a small amount of water on the ground, but could not determine where it had come from. Once the engine had cooled down, I checked the fluid level, and is was very low (I ended up adding a little over a gallon of coolant). Decided to keep an eye on it , and had no problems until Late june when it did the same thing. Repeat check and still no signs of any leakage. Then it happened again last night about a mile from my house. With the exception of the first time, it never got to the 'hot' mark on the gauge, and in the case of last night I noticed the gauge went back to normal when the truck was moving (I noticed it climbing while at a traffic light.

I have checked the oil for foaming (none)
The engine does not idle any differently then before the problem started back in April
Each time it happened, the ambient temperature has been over 100 degree outside (we live south of Sacramento Ca.)

I am at a loss as to what to check next. Planning on doing a pressure check on the system, but am curious if there is anything else I should be checking that maybe I'm not thinking of.
Thanks in advance for any advice from the Explorer hive mind.

Chris DeRoos
2004 Ford Explorer

 

[Drewmcg]

In my experience, these 4.0L SOHC engines do not frequently blow head gaskets. However, its always a possibility if the engine is seriously overheated (These have cast iron blocks and aluminum heads). If you blew a head gasket, it would not necessarily result in foaming oil. There is a test that involves checking either the coolant or the gases in the coolant reservoir for indications of gas or combustion products. You need a tool for this; I don't know how much they cost.

You don't mention how many miles on your 'sploder. Radiators don't last forever, and over 100 degrees F is very hot. Could be that the cooling capacity of your old/OEM radiator is limited. Radiators are not all that expensive (see Rockauto), but in my experience its a super PITA to replace them on this model. (Do a lot of YouTube searches for shortcuts if you go this route.) Do-able, but difficult.

Another weak spot on this engine is the plastic thermostat housing (where your thermostat was sandwiched into). They are prone to leaking/failing. Presumably there was no sign of this if your mechanic did not replace it, but that wouldn't stop it from failing afterwards--either independently, or as a delayed result of the original overheating. I've replaced these three or four times on three different 4.0 SOHC engines. Be very careful to get a good, six-point socket of the correct size on the lower housing bolts, and to use never-seize on the threads when you reinstall them (consider replacing them, too). Mind the odd round, flat gasket between the lower housing and the block (i.e., don't forget it). If you buy OEM parts, you need to order it separately. Most aftermarket parts include it. There is no separate gasket between the lower and upper housing; the rubber gasket on the thermostat provides the seal.

Someone made an aftermarket metal thermostat housing, available on ebay (I think). Search this forum if you're interested. I'm sticking with the plastic ones up here in Michigan.

With the exception of the thermostat housing (which seems to be a game of roulette no matter whose part you buy), I'd recommend OEM (Motorcraft parts). Especially for the thermostat--which is pretty cheap. I don't know when Ford changed from a mechanical to electric fan clutch, but it would seem to be pretty simple to check whether your fan is spinning at high speed when its hot out. Just look/listen!

Fan, water pump, radiator, thermostat, housing, hoses, quality coolant -- that's about it for a good engine. If its not one of those, suspect a blown head gasket. NB: I had the heads restored by a machine shop on one of these engines -- not outrageously expensive. Get a friend to help you reinstall them, with new headbolts (which require a lot of strength to torque properly). I found the German valve cover gaskets (Mahle) worked better than the Felpro ones, but was happy with Felpro's head gaskets. good luck!

 

[TechGuru]

The two things I would suspect are

1. Bad fan clutch (what brand did you replace it with?)

and

2. Bad cap not maintaining enough pressure causing boil over.

Be sure you're running a 50/50 mixture of coolant.