Temperature Fluctuation

[burntmetal]

Good afternoon. I've put about 2500 miles on the 96 Explorer now and since I've been driving it i always noticed the temperature gauge fluctuates. Not by a few degrees but will get up about 2/3 of the gauge then drop suddenly to about a 1/4 then slowly climb up again and repeat. I had only driven it 50 miles or less on trips till last Sunday when I went about 80 miles. I was going about 75 when I noticed it had climbed almost to the top of the gauge. Pulled over and noticed the top radiator hose was super pressurized. I let it cool a but then popped the cap with a towel, lots of steam and a gush of the new coolant I put in a month ago. I sat a but longer and topped it back off and finished my trip. I installed a new thermostat yesterday but the fluctuation continues. Any ideas what could be causing this? Thanks.

 

[Redmanss]

Happening at speed it sounds like a clogged coolant system, either in a hose or the radiator. Drain it, look for foreign matter, and flush/fill it. Does the fan clutch seem to be working properly?

Alternatively, could be the water pump, would definitely give that a hard look and inspection for any leaks, noises, belt wear, etc.

 

[J_C]

Any chance you just have a bad radiator cap?

 

[96eb96]

I would pressure test the cooling system, you can rent it at a parts store. Sounds like another cracked head, that is my first guess. There are a few solutions.

 

[burntmetal]

Happening at speed it sounds like a clogged coolant system, either in a hose or the radiator. Drain it, look for foreign matter, and flush/fill it. Does the fan clutch seem to be working properly?

Alternatively, could be the water pump, would definitely give that a hard look and inspection for any leaks, noises, belt wear, etc.

When I first got the vehicle I drained and refilled with fresh coolant. I didn't really notice any heavy rust or anything in the old coolant(it had sat for 2 years which was why I replaced it). The fan clutch seems to work as it should and it does not leak coolant. I think I may add some coolant system flush to it and change it again. I may change the cap just to do it then take a look at at new water pump. Probably should with over 200k on it anyway. Thanks.

 

[burntmetal]

I would pressure test the cooling system, you can rent it at a parts store. Sounds like another cracked head, that is my first guess. There are a few solutions.

I hope not. What are some other symptoms of a cracked head that I can look for?

 

[J_C]

^ Bubbles coming out the coolant expansion tank, white smoke out the exhaust, loss of coolant, coolant in oil. In addition to pressure testing there are also test kits for exhaust gas in the coolant expansion tank, run about $35 and up on Amazon, etc.

However I don't think there is a way to be sure it's a cracked head until you tear it down and find the crack (or see a leak externally), versus a head gasket or warped head.

 

[burntmetal]

^ Bubbles coming out the coolant expansion tank, white smoke out the exhaust, loss of coolant, coolant in oil. In addition to pressure testing there are also test kits for exhaust gas in the coolant expansion tank, run about $35 and up on Amazon, etc.

However I don't think there is a way to be sure it's a cracked head until you tear it down and find the crack (or see a leak externally), versus a head gasket or warped head.

I don't think I have a cracked head then. System holds pressure, exhaust is smoke free, and it doesn' seem to loose coolant. I think it' the water pump so I'll probably replace it soon. Thanks for the quick reply though.

 

[koda2000]

There's only so much checking you can do for a possible cracked head (@J_C covered some ways to check). The only way to know for sure is to pull the head and examine it visually, or by magne-fluxing. Some cracks are easy to see with the naked eye, and some are not. If you ever said which engine you have I missed it. Head cracks between the valves are pretty common on the OHV V6.

 

[96eb96]

I don't think I have a cracked head then. System holds pressure, exhaust is smoke free, and it doesn' seem to loose coolant. I think it' the water pump so I'll probably replace it soon. Thanks for the quick reply though.

There are a few things with these trucks...
Yes, they do crack heads, but you would also notice misfires at startup, maybe not. Sometimes you won't see symptoms for years.
These engines have issues with steam formation and gauge fluctuation. There was a TSB somewhere. Maybe related to the cracked head issue. Mine would fluctuate between 1/4 and 1/2.
The WP could an issue,I believe it was revised.
The single wire sender could also be defective, you can also monitor ECT with a real scan tool.
There is a chance the radiator is clogged too. Who knows what the last owner did. Maybe worth running one of those flush chemicals thru.

Opening hot coolant and getting a gush could be normal.

 

[roscoe 0202]

check the bottom radiator hose it may be collapsing from vacuum from water pump old hoses used to have a spring inside to stop this
roscor

 

[Turdle]

^^ this, and, are you sure you burped all the air out of the system when you refilled the coolant? Stuck thermostat also comes to mind

 

[lobo411]

are you sure you burped all the air out of the system when you refilled the coolant?

Yep, my thoughts exactly. If it were me, the first thing I'd check would be the easy stuff: make sure the system has been purged of air, check for obvious external leaks, replace the radiator cap unless it's already brand new.

 

[96eb96]

Many years ago I worked in shop. A 3.8L Taurus engine came in, overheating, etc. Those are notorious for HGS. Ok, right away, the tech tears it down, replaces the gaskets. Leaves it outside for the owner to pick up the next day. Owner calls back and said the problem is still there, send a tow.

Make a long story short, turned out to be a bad radiator cap. I replace all those cheap things every other time I service the coolant and keep a spare.

These OHV engines are also weird, they have the bypass built into the engine (it is not external). That sometimes causes issues if something isn't right in the cooling system.