2003 Odd cooling issue

[tper94]

I have a 2003 Explorer XLT with a 4.0 v6 4x4. I’ve been trying to figure this out for months now.

Every time I drive the car from C it briefly overheats. The temp gauge rises like normal, but when it reaches operational temp the gauge spikes into the red for about 2-5 seconds and falls back down to normal temp. The rise and fall to and from red lasts about 3 seconds each. From that point on it drives as it should. I could run it out of gas if I wanted. (For future reference. This paragraph is “the thing” haha)

It loses fluid and I have to add some at least every month or two, so not quickly. I don’t check every time I drive, but I believe it’s mostly lost through the reservoir cap. The system seems to not have any signs of leaking elsewhere. I flushed the system and refilled at one point using a vacuum tool to remove all the air and it held the vacuum steady. No signs of weeping from the water pump as it’s pumping properly.

I most recently burped the system two days ago with the nose up in the air and the tires about a foot and a half off the ground. That appeared to solve the problem, but the issue came back today. Test drove it yesterday from C and it was fine. Today it did “the thing.” Drove it about 25 miles the rest of the way home and it did great.

No colored exhaust, or milky colored oil so I’m not leaning toward a blown head gasket. I found some threads on here talking about the reservoir cap (no radiator cap on this one). Could it be holding pressure instead of releasing it forcing an air pocket to develop somewhere?

Parts I have replaced: radiator, thermostat (twice. One aftermarket. Currently an OEM), and thermostat housing (cracked))

 

[TechGuru]

Since you've already replaced the thermostat with a Motorcraft 190F I would try replacing both the cap and the sensor.

 

[tper94]

Since you've already replaced the thermostat with a Motorcraft 190F I would try replacing both the cap and the sensor.

I had someone recommend that to me the other day, so I ordered them both. I’ll be out of town a few days, so I guess we’ll see what happens on Monday.

 

[Joe in NY]

Under pressure air bubbles will be tiny. Not under pressure they will be big.

It sounds like a case of bad head-gasket to me but that is due to a recent experience. Drinks a little coolant. After you drive, park, and go back driving it'll over heat but if you keep driving it goes back to normal. For me though, if I stopped it would over heat really bad. Had to keep the RPMs up and air going through the radiator.

 

[tper94]

Under pressure air bubbles will be tiny. Not under pressure they will be big.

It sounds like a case of bad head-gasket to me but that is due to a recent experience. Drinks a little coolant. After you drive, park, and go back driving it'll over heat but if you keep driving it goes back to normal. For me though, if I stopped it would over heat really bad. Had to keep the RPMs up and air going through the radiator.

For me, I have no issues at idle. Only when it quickly overheats about 1-2 miles after driving from C and then stabilizes. I’m not even quite sure if it’s actually overheating or getting a bad signal. I don’t think it’s going to change temperatures as fast as my gauge moves.

Also, it doesn’t overheat if I start the vehicle from c and let it warm up to temp. Only if I drive it immediately after starting.

 

[Drewmcg]

You describe two problems: a temp guage (3-second) reading hot and lost fluid.

Problem #1: Have you replaced the sensor? If so, and you're still having this problem, then check the sensor wiring. Even if there was air in the system, it would not explain that spike (I don't think);

Problem #2: Well, the coolant is going somewhere! Absent a bad hose/clamp, its most likely either (a) the thermostat housing; or (b) the head gasket.

The thermostat housings on these engines are a sore spot. They fail frequently. Sometimes its the weird flat/round gasket (sold separately by Ford) between the bottom of the lower housing and the block. Sometimes its the lower housing. Sometimes its the upper housing (the part that sits on top ofthe thermostat). Make sure whoever changed the thermostat last flipped the side with the rubber gasket surface face up (it creates the seal with the upper housing).

Given the frequency of thermostat housing failures, I'd say buy a complete aftermarket housing (they're not that expensive) and install it (you can use the old existing OEM thermostat) and see if there's an improvement. Use never-seize on the bolts (especially the lower bolts) for the housing. Good luck.