3.3L engine, 71,000 miles. Coolant flushed at 50,000 miles, waterpump went bad at 69,000 miles and was replaced.

Everything working great, then it suddenly starts overheating. Gauge shows hot, upper rad. hose is hot to the touch. Heater hoses, lower rad. hose, cap, all cool. Sounded like a typical thermostat stuck closed.

1. Changed thermostat, no difference
2. coolant looks clean, no leaks
3. Oil looks clean
4. Is now at a mechanic. They suspect an airlock, but haven't been able to clear it. They say thermostat is good, and water pump is working.

HELP! My ideas of the problem.
1. Radiator blocked? System looks clean.
2. Water pump works fine at idle, but isn't pumping at driving conditions? Impeller/shaft slipping on a new pump?
3. Blown head gasket? No tailpipe steam, oil and coolant look perfect.
4. An airlock put into the system when I changed the thermostat? That won't clear out?

Any help is greatly appreciated. Trying to get some ideas to help the mechanic.

 

In order for the top rad hose to be hot, the thermostat would have to be open. Flow in the radiator is from the top down.
Water pump should be hauling coolant from the bottom radiator hose and circulating it through the system.
Blockage of some sort somewhere, it seems. Are you sure the rad is full? Low fluid level will cause loss of heat in the heater core. Don't depend on the reservoir for the fluid level, check the rad.

 

Thanks for the reply, TJeepman. I should have put this info in the original post.

Coolant level is good in the radiator. With engine off, I can remove the cap while the guage shows hot, not usually a good idea. Some pressure will bleed off, coolant comes out if the cap is opened too quickly. I should have been scalded doing that, but the coolant at the cap isn't hot.

When the problem is found, I'll post it here. I sure hope it was a bad t-stat at first, then I airlocked it changing the t-stat.

 

Two things:
(1) Perhaps your temperature sensor is wacky and (2) your new thermostat is stuck wide open. Did you use one of those fail safe thermostats? They can go into fail safe mode pretty quick sometimes if there is air in the system.
They say to fill the system up with the front end (high point in the system) up slightly. Is yours sloping down by any chance?

 

if yalls upper hose is hot, then the thermostat is opening. if no heat in the interior, then no have an issue with an air lock.
blown head gasket, coolant in oil take off filler cap and look for slimey stuff or when yall just start it up when cold, squeeze upper hose if not hard/pressurized no gasket prob there besides probalbly have a missfire too.

i fixed a lebaron that no-one could figgure out why it was overheating. one shop put in a new stat, one put on a new head gasket, one put on a head, when i got it, i found that someone put some cardboard between the rad and a/c. so duh its gonnna overheat.

are the fans comming on, do they feel hot air comming out with a lot of wind? could the rad be plugging up and not letting good flow thru the cores? i fixed a spirit that was overheating cuz the rad was plugged up. i figure it out when temp hit 212 and the fans came on and not much heat on the lower rad hose side. i used a temp probe down the filler neck and saw not much temp near the bottome. after i pulled the rad and put in a new one, i cut apart the old one and found she was really junked up with stop leak.

 

(1) Just talked to the mechanic. His temp. gun confirmed it is hot. Temp guage is probably accurate.

(2) Don't know about the fail safe. It was a $10 t-stat from O'Reilly's, made by Murray

Vehicle was at a very slight up angle when refilled after changing t-stat.

I had a similar problem with an 1987 Shadow (in the galleries, the black CSX). Heater core was plugged, and the valve that controls flow to the core broke. Replaced valve, backflushed core but it didn't clear it 100%. Now, I just flip the climate control to recirc, which cuts off flow to the heater core, and no overheating.

So...I wonder, could there be an airlock in the heater core of the van? Could the heater core be located where it won't "burp" unless the outlet hose is disconnected? We might be able to test it by running the climate control with the recirc feature on. If it has a valve to bypass the heater core, that would be a clue.

Grasping at straws, but that's about all thats left.

 

Thanks for the reply Circumventor. Fans are coming on, both when the engine temp gets high, and when you turn up the AC.

It's never had stop leak in it. Water pump was changed about 2000 miles ago. Could some gasket sealant been squeezed inside the pump, been floating around the system for a couple of months before causing a clog?

I'm in denial about a blown head gasket. But there is no tailpipe steam or signs of oil contamination.

 

i just was thinking back to my 1964 fairlane that i had put a brand new water pump on and it overheated on me, did the rad replacement, stat, hoses and what ever else i could think of turned out the new pump was junk the impellr was slipping on the shaft. seems yall mite have the same prob since there was no prob before the pump 2k miles ago. sumthing to think about.

 

Yes, sometimes new parts aren't what they are suppose to be. I once replaced a Ford carburetor, and the replacement performed worse than the old one. Removed the air mix screws from the old one, found fine steel wool like metal in the passages, removed it, put the carburetor back on and it worked great. Took the newly purchased carburetor back.
Came across a site, a month or so back, where a repair shop listed replacement parts that had been purchased, that were defective. The % was fairly high. So, your water pump is a suspect for sure.

Considering that the radiator and the heater are separate, shouldn't coolant be flowing through your heaters even if your radiator were plugged or there's an air pocket somewhere? The problem is looking even more like the water pump.

 

I agree that it sounds like the impellers are seperated from the shaft on the water pump, but I was told the water pump tests fine.

It's still in the shop, but they had appointments booked today and didn't get to spend much time on it.

I was told they have one of those vacuum machines that will drain and fill, and get rid of air locks. That will be attempted Friday.