My '99 started to overheat several months ago---on the highway--after about 2 hours of continuous driving in cold weather. Pulled over right before needle got to the "red zone". Popped hood and the overflow tank was overflowing with boiling coolant. Once it cooled a bit, i pulled the radiator cap off---ran for a few minutes and went on my way. No problems for another 30 minutes of driving. Shop pressure tested and everything checked out fine. Replaced thermostat for good measure. All good for a a few months.

A few weeks ago, I noticed that temp gauge would start heading north after getting off the highway. Once I sped up again, the gauge would go back down. Never went all the way up. I replaced radiator cap and it seemed to get a little better.

Then, last week, gauge shoots way up after an hour's worth of highway driving (granted it was almost 100 degrees). I pull over and --- once again--overflow tank is full and boiling over with coolant. Let it cool, pull off cap, top of coolant---that would get me another 5-10 minutes on the highway. Limped home without truly overheating.

What would cause the coolant to boil over into the resevoir like that? Seemed like a pressure issue but could this be a water pump problem? Clogged radiator?

Thanks,

 

Plugged radiator tubes or debris in the fins. Could also be water pump vanes are eroded away.

 

That's your answer right there. Replace the radiator and chances are some of that debris got to your heater core. When winter rolls around again and your heat is not as strong, you would know why.

 

Are the fans (both of them) on and on high speed when this is happening?

 

Plugged radiator sounds logical--especially given the rusty brown color of the coolant that is in the overflow resevoir.

In terms of the fans--they definitely both run on high (at least now). In terms of whether they were running when the overheating occurred----I believe so---but I cannot say for certain.

Thanks!!

 

I was actually referring to leaves and bugs stuck to the radiator fins. When I replaced my radiator it was pretty plugged up externally.

 

Oh. I was referring to sludge in the coolant clogging the fins if the coolant wasn't replaced in years.

 

Ah---the plot thickens. I was prepared to take the radiator out this weekend and give it a good cleaning. That said I needed to take the car out on a short run this week so I decided to get the car heated up before I left to ensure that it wasn't going to quit on me as soon as I got on the road. Took rad cap off and let it run----revving it every once in a while---just to ensure I got any air out of the system. Sure enough there were some air bubbles that bubbled out. Took the car out for 1/2 hour...no problems.

Then, on the way home---temp gauge stayed where it had for years---slightly below halfway mark. All good---all of a sudden the needle goes all the way down past COLD as if the engine was off. Stayed there for a while and then, evenually went back up to the 'just shy of midway mark'. I'm still going to tackle the radiator as it seems like it's contributing to the problem but it looks like the temp sending unit (or whatever it's called) is acting up as well.

 

u sure the radiator cap is still good? The boiling fluid in the reservoir leads me to believe the system is not holding pressure or not circulating through the radiator.

Dont replace the radiator just yet. Flush water through it and clean the exterior. If its not leakin and water flows freely, then the radiator is not busted.

Replace the ECTS. Its 25 bucks and easy to replace. U can test it, but for 25 bucks why waste the time IMO.

It the radiator is fine, thermostat is fine, ECTS is fine, then flush the entire cooling system.

If the car is still overheating, then your water pump is toast.

 

With our cars, I agree, it's likely the radiator, esp. if the thermostat is new.

Newer cars, you get into electric water pumps and it gets trickier to diagnose....but I feel like ours are simple and a radiator is not very expensive anymore....

 

sounds like thermostat is sticking, system probably sludged up. depending on your budget, I would first replace thermostat, next radiator, last water pump... but start with a good flush of the system first...

 

my 96 se is still acting up after new radiator,thermosat and both temp sensors.It goes way over the happy medium and stays just below the hot mark. water pump is moveing the water, relays tested fine. Any help would be helpful

 

In your one post you said that you had rusty brown water in the reservoir. That means that all the anti-corrosion chemicals in your antifreeze were used up. So that could mean that your water pump is screwed, like asand1 said. You say that the water pump is moving the water, but it may not be at the full force/volume.

photos courtesy of org member Nelsito65:





When you look at the center hub of the old pump, it is coated with a brown slime. That should not be. I can guarantee you that every surface in that cooling system was coated like that. That junk would be in the radiator and when you took the cap off, it would be on the bottom of the cap.