99 Explorer Temp Gauge Going Crazy

[19redbird90]

Very strange behavior I can’t figure out on my 99 Explorer 5.0. Last week (100-degrees for four days straight), my temp gauge started going crazy. Once it reaches normal running temp, it skyrockets past the “H”. When I accelerate it goes back to normal. When I brake, it goes back to normal (weird). Going down the highway, it jumps all over the place, almost like a sloshing effect. I changed the temp sending unit…no luck. Replaced the t-stat…no luck. No noise from the pump and no water from the weep hole. No coolant loss at all.

Here’s the kicker–I realized a few days ago that this does not happen after dark when the ambient (outside) temp is below 80-degrees or so. That would seem to rule out a gasket or head problem (also have no oil in coolant, no coolant in oil and no white smoke). Car runs and sounds fine. My most recent theory was I might have air trapped in the system. I did have the car flushed last winter when the heat wasn’t as warm as it should’ve been. I thought maybe the tech let air in…so I tried to burp it today. With the front elevated, defrost on high, radiator cap off and engine running (from cold start), I could not see any air come out of the filler neck. However, I didn’t see much of anything happening. I thought once the t-stat opened, the water level would drop as it flowed. Not only did it not drop, it just continually overflowed coolant (very slowly) out of the filler neck long after the stat opened and the upper hose was hot.

Important note: Last week it was just the gauge going nuts in hot weather. This week, the message center will also occasionally tell me “check engine temp”. When it does, I accelerate quickly, the gauge goes down and the message goes away.

What am I missing??

 

[Zulu95]

Fan clutch?

 

[windsors03cobra]

Possible clogged rad, or a head gasket.

 

[19redbird90]

The fan seems to kick in like is should. I've thought about a clogged radiator after NOT seeing the fluid drop with the cap off today. What's the best way to unclog?

Also wanted to ask about the upper hose. It goes upward after the stat, then back down into the radiator. Is there a chance a bubble is still trapped in there if I didn't have the front of the car high enough during my burp attempt?

 

[19redbird90]

Update: I checked the fan clutch. No bearing play and it spins freely but doesn't freewheel. Flushed the radiator completely (through upper hose and filler neck up top, out drain and lower hose on bottom). Got some crud but nothing too terrible. Flushed the reservoir. Drove to town and nothing has changed.

Did notice something I hadn't before...the gauge goes back toward normal when cornering, much like it does when accelerating and braking. Also noticed it dips back toward normal each time the car shifts gears, then bounces around and climbs back to hot. Almost like any g-force from any direction fixes the problem for a few seconds creating the sloshing effect I mentioned before (I'd like to post a pic of how far past the "H" it goes but can figure out how on a Mac). If you saw it, you'd see there is no way I could drive this thing THAT hot for over 2 weeks without serious problems. The car is still running fine. The only thing really left is the water pump, but the upper hose is getting hot like it should if water is pumping through the system. Could it simply be the gauge?

 

[rickybobby]

It sounds to me like you have a broken wire somewhere. when the engine moves it makes or loses contact. Not sure how to explain it working fine when the ambient temp cools though. that could be the insulation contracting a bit but i doubt that.

 

[19redbird90]

It kinda acts that way. Someone also wondered if the circuit board behind the gauges has warped in the abnormally extreme heat we've had (for WI anyway), and a contact is being compromised somewhere. Something I forgot to mention...I took EXTRA care when refilling the system today to eliminate the air bubble theory. Maybe I just need to buy an aftermarket gauge to see what's really happening...

 

[Jstcruz]

I read on here somewhere that a faulty rad cap will cause the gauge to wonder around. Its a cheap attempt at fixing the issue

 

[19redbird90]

Yeah, the radiator cap and water pump will most likely be replaced this weekend. I'm also going to do a full flush with the pump off. Aside from bugs in the grates, that's about all that's left. I just got back from driving it again and it seems marginally better. I wonder if the sediment I removed from the radiator this morning helped a little. Oddly enough, I also realized the gauge reading goes to normal in the middle of a left turn, not right. More and more bizarre.

I haven't mentioned this car has 259K. I am the principal mechanic and have kept up very well with maintenance, fluid changes, etc. The only time I've had someone else work on it was the flush last winter (my wife needed heat NOW). I wonder if they just flushed the heater core and nothing else. With this many miles, maybe there's just a crap ton of crud throughout the system creating hot spots.

 

[19redbird90]

Update: New water pump did the trick...finished it last night. It was 99-degrees outside today and no gauge issues at all. Unbelievable. Impossible to diagnose with no bearing chirp and no water from the weep hole.

Word of caution to those removing the water pump on older Explorers, expect the bolts on each end of the pump to break off. Mine did, and I saw MANY posts here with the same problem. What a freaking mess. I had to take the angle grinder and carefully cut the pump off the timing cover. After the cut, I was left with about 3/4-inch of bolt to grab onto. Talked to a mechanic friend who tells me he's done the same thing on many Explorers and had to cut off the timing cover. Nonsense! Easy to say when it's not YOUR money. I used a 5/16 expansion extractor (my new best friend), along with multiple rounds of heat and PB Blaster, and slowly turned them out. Attempting to pry the pump off with all the water pump bolts (which double as upper timing cover bolts) removed, I cracked the seal on the timing cover gasket. So I went ahead and replaced that while I was there fearing I might have coolant entering the oil pan.

I don't wish this job on anyone, but rather than fight it, just cut the pump body if your bolts snap. It will save you tons of grief.

 

[Jstcruz]

I appreciate the info!