I have a problem with my truck. The temperature gauge will fluctuate and rise quickly and my check gauge will come on. I have an aftermarket overflow reservoir and I noticed that when the gauge does this, the cap had popped off of the reservoir and it's overheating. What could be causing this problem? Could my thermostat be bad and causing this? Also, I changed the thermostat and radiator cap, but those didn't help. What else could be causing the truck to run really hot and blow off the coolant reservoir cap? I was driving my truck on 95 and it started to overheat. I looked under the hood and sure enough the cap and come off of the reservoir again. How can I fix this? Could it be the water pump? I haven't done a fluid change in a while, so I'm due; could that cause it too?

 

That is probably blowing off due to the pressure and expansion. The tank however has NOTHING to do with the overheating. The tank is where the coolant goes AFTER it is overheating and is over pressurizig.

The cause of overheating could be several things. However, if it does this while moving then it is definately something preventing the circulation of coolant. Our trucks will keep themselves cool without a fan as long as you're moving. It won't get hot until you've been sitting idle for 5 or 10 minutes. I would start with the coolant level, water pump, and thermostat. Any of those will prevent coolant from circulating through the radiator and it will boil over.

 

Dammit, thought you would say water pump. I changed the t-stat and checked the coolant level. Guess it may have to be the water pump.

 

check the weep hole on the waterpump to see if coolant is seeping out. if it is that means your pump is bad

 

Well, there's nothing coming out of the weep hole - does that mean it's not the water pump?

 

This sounds like your coolant system is low. Check it first thing in the morning at the radiator. Make sure its full to the cap. Next thing, since you said you just replaced the thermostat, I would suspect is an air bubble in the system. If you can, raise the front of the truck. Start the engine with the radiator cap off, let it warm up till you see coolant moving past the cap opening. You may notice some burping, if it does rev the engine up 2500 rpm then to idle a few times to help clear any air in the system. Add additional coolant if needed and put the cap on. If you have a friend to help when your ready to put the cap on have them rev the engine to 2500 and hold it, then add coolant if needed and put the cap on then return to idle.

The overflow bottle cap should not blow off under any circumstances. There should be a vent in the cap otherwise the system wont be able to equalize (coolant wont flow to the bottle when hot and it wont allow vacuum to pull back when it gets cold). Not sure were you got the overflow bottle at, but I would either replace it with a factory reservoir or one that you know for sure works with your truck. Also make sure you got the right pressure relief cap on the radiator.

 

Well, I've done a good flush, fluid change, changed the thermostat, hoses, radiator cap, reservoir tank, belt, and radiator. Would changing the water pump help? How can I tell if there is something more serious occurring internally?

 

Well, if it is still overheating, the water pump is the only thing left.

 

What if the water pump doesn't fix it, what else could it be?

 

I had some heat a few days ago (even after the problem started). However, I didn't have any yesterday after I put the new belt in and radiator in.

 

bite the bullet and change the waterpump......good luck and have fun.....

 

Head gasket... If you weren't getting flow from the water pump or thermostat, the coolant in the radiator wouldn't be hot only the coolant in the block. Your coolant system is only running 16 psi which isn't enough to pop off a cap. The combustion chamber is over 100 psi and when that pressure enters the system it will blow off the cap. Don't forget to check your oil and make sure it's not milky. But I'd guess and say head gaskets.

 

I changed the water pump and it seems to have worked. I took it around the block 4 times after it was already warmed up, and then went for a 2 mile round trip with a max speed of 50 mph. It stayed in the middle as far as temp goes. The cap didn't pop off. However, it appeared to be working properly after every fix I tried until the next day when I'd drive it around. So, I guess I won't know until tomorrow when I drive it to work and back.

I'm positive the belt is on right. I'm pretty sure I got all the air out of the system.

Also, the cap was popping off because of the coolant flowing out of it - it wasn't the air. It was only popping off before I added the vent. With the vent, the coolant just flowed right out of the vent.

 

how long did the water pump replacment take? im thinking of doing mine before it fails. i just hit 140k

 

Good thing that fixed it! only thing left would have been a blown head gasket or cracked heads! very $$$$ and time consuming!

 

Well, I hope it fixed it. I won't know until tomorrow - it never gives me problems until the next day.

The water pump took about 3 hours to install, and that was at a leisurely pace. It took me a while to take it apart because I couldn't figure out how to loosen the bracket that holds the ac compressor and power steering pump. That bracket blocks one of the bolts completely and makes it a pain to take apart. Two bolts that hold it down are behind the tensioner.

Oh, and my truck has 140k on it as well. I guess that's the life expectancy of a water pump.

 

dammit, im at 134k........

 

Water pump didn't work. I drove it about the same distance (as last night) after it had warmed up (much like yesterday), got to burger king and parked it. I revved up to 4k for a few seconds, let off, still normal temp. Looked under the hood and the reservoir cap had blown off and coolant had surged out a bit. I replaced the cap and grabbed some food to go, and started driving home (less than a mile). The temperature guage dropped to just above C. It then went straight to the middle of the gauge. I continued driving and the temperature started rising. It was stop and go traffic, with street lights and when I'd stop it'd drop some. I'd go for a few blocks more (max rpm of 3k and top speed of 50-55 mph) and the temp would rise beyond the mid point and just shy of H (red). It would drop a bit when I put it back in park and it started to rise a bit and stabilize around 60-75%. I checked the cap again and it was not displaced; but it had been overheating. What's everyone got for me?

 

It's a head gasket... You keep driving it you'll put a motor in it sooner than you know.

 

Coolant doesn't usually leak out of the spark plug holes unless it's extremely bad. In which case the motor has usually hyrdolocked already. There are no TSB's on a Head Gasket or Cylinder head issue for a 2000 3.0 listed. It takes a crack about the size of your fingernail in a head or head gasket to cause this. Either way you're pulling the heads off. And when you do head gaskets you need to have the heads sent out and checked/milled anyways. You can pressure test the system but if it's only overheating when it's hot it might well pressure test fine due to the expansion and contraction of metals.

 

I didn't have any coolant in my oil. However, I'm not ruling out the head gasket or cylinder head itself.

I'm going to try the intake manifold gaskets tomorrow - they're cheap and they're easy to change so I might as well try it before I go elbow deep to the heads themselves. It could be a possible fix.

I'm fortunate that my lil' bro and I live and work together, so I haven't had to drive my truck except to see if I made a change that fixed my problem.