1999 Ford Explorer

[xVersa]

Hey guys, this is my first post. I've read quite a bit on this website so I thought I'd register.

Anyways, I've found a 1999 Ford Explorer on craigslist for a good price, but he says that the temp gauge fluctuates for the first 5 minutes of driving, then stays in the middle. He believes it's a blown head gasket, but I'm doubting that because it never overheats, the oil is clean, the coolant never leaks and is clean. There's other ways to diagnose a blown head gasket, but I would think there would be a more glaring issue with the truck.

I've seen a lot of threads about these temp gauge fluctuations, but never like this (although this case is milder than the ones I've seen). Do you think it is as simple as a bad temp sending unit?

Thanks for reading and helping me out

 

[koda2000]

I'm thinking bad thermostat.

 

[chefduane]

+1. I'd start with the thermostat - fairly straightforward to do. Buy a new housing when you do the thermostat, tho. They tend to crack easily and especially when replacing the thermostat. (Don't ask me how I know this, but I'm not the only one.)

 

[Flash]

The first and most important thing about buying a 1999 or any year V6 SOHC is the timing chain guides and tensioners.
Listen very carefully when the engine first starts from cold, if you hear any timing chain rattle, run, don't walk. If it's a tiny rattle then a tensioner replacement will most likely cure it.
If the tensioner is bad the chain will rattle at start up until the oil pressure builds up.
During that time the chain will thrash about and carve up the plastic chain guides.
That's why rattle is a big no no. Later models and upgrade kits have a steel backed chain guide.

The temp gauge fluctuation IMO isn't a big deal as long as you're 100% confident that the head is sealed.
Look at the coolant; is it clean and the right colour?
Using straight water is a short cut to wrecking your head.

I'd look at replacing the sender, the thermostat and the housing.
Do it all together as they're all in the same place and don't be tempted to put in a lower temp thermo.

 

[Flash]

Hey guys, this is my first post. I've read quite a bit on this website so I thought I'd register.

Just a tip; put your location in the ID thing in the side panel so we know what kind of conditions your truck is expected to see and what it's been through already.
IE: desert, rust belt etc.

Though it still doesn't stop people from suggesting I pop into Pep Boys or Harbor freight.

When you buy the Explorer put that in the sig too so we know if you have a SOHC, OHV or V8.

 

[Mike65]

Welcome. I agree with the above, start with a new thermostat.

 

[Sedition]

It is the Thermostat, change the o-ring too.