Overheating withheater on?

[StillKicken]

I just replaced my water pump this saturday. Have done this before several times. Once on this explorer. Replaced thermostat while I was in there.

Now, idling, driving, accelerating, accelerating uphill....no problems. Water temp. gauge stays right at "N" or "O" in normal. When I turn the heater on, it starts to overheat. All the way upto "L". Stays there for about 4 seconds, then drops back to "N".

I always heard that if it starts to overheat, turn your heater on and it will "suck" the heat out of the engine bay and drop the temp. But this is the complete opposite.

Radiater replaced about 6 months ago. System flushed when that was done.

Could this be a hose collapsing? The lower one or the hose coming from the heater control valve to the water pump?

Odd...

 

[Anime]

My first guess would be it has something to do with the thermostat, since nearly every overheating problem I've ever encountered came down to the thermostat. A small defect or something could make it defective, even brand new. That said, you might want to check your hoses to the heater core, they go into the firewall and are pretty easy to replace with the coolant drained. It's also possible theres some restriction in the heater core which is blocking the coolant flow, and it starts overheating until the pressure builds up and forces the coolant through. If it continues to do this 100% of the time when the heat is turned on, my suggestion would be flushing the heater core, replacing the hoses to and from it, and seeing what happens from there. If that doesn't help, pulling the core to check it out and/or replace it might be in order.

 

[gijoecam]

Hmmm... this one's got me stumped... My best guess is that when you turn the heat on, the heater control valve opens, filling the heater core with fresh warm coolant and dumping the cold coolant back into the system. Then, since the system is a bit cooler, the thermostat closes a bit to bring the head temp back up, and then sticks at that semi-restricted position. As it heats up, it opens again, eventually settling in the proper operating opening.

I doubt the heater core blockage could cause the issue. Coolant isn't forced through the core as a primary means of cooling, it's a kidney loop. You could bypass the heater core all together and cap the lines and the engine wouldn't have any issues with overheating. The heater core can certainly draw heat off the engine, but it's not going to add heat to the system. That would violate more than a few thermodynamic laws.

Now, another possibility that comes to mind is that somehow air might be getting trapped in teh head. When you installed the t-stat, did you orient it in such a way that the little bleeder check ball was at the 12:00 position?

The only other possibility that comes to mind is that the heater core is somehow letting the system maintain its pressure, and it's actually on the verge of boiling over or is, in fact, boiling in the head, introducing air into the head, and throwing the t-stat for a loop. When you refilled the coolant, did you mix it 50/50 with water?

-Joe

 

[StillKicken]

I positioned bleeder valve in the 12:00 position. I also mixed the coolant 50/50.

Is it a possibilty that the hoses perform as they should in normal driving, but when I turn on the heater, the heater contorl valve opens, making more of a demand and the extra pressure collapses the lower coolant hose?

Sounds like I am trying to align stars here.

Thanks for the suggestions. Helps me think also.

 

[StillKicken]

ok, So i replaced the heater control valve and temp sending unit. Still no luck. Now I have another problem. Usually when I turn the selector switch from vent, floor or whatever back to off and turn the fan off...it'll stop. Now with fan off and selector switch off...heat still comes out of the vents.
Please help me before I go crazy!

 

[StillKicken]

Fixed!

I wanted to post this as I hate it when I am doing a search, person had a problem...but never how it turned out!

Today I replaced the lower radiater hose, hoses to heater control valve, temp. sending unit and the thermostat. I origionally had a 195 thermostat and replaced that one with another 195 when I did the water pump. Today I put in a 180 degree.

Everything is fine so far!

I also fixed the problem I had posted in #5. I am guessing when I relppaced the heater control valve, that I did not rehook the vacuum hose to the valve. Either that or my 2 year old undid it. He was helping! He has a lot to learn! Bt believe it or not, he is a BIG help. He is learning what the names of the tools are!

One other thing to help that I learned today. For the PITA screw to reach when you are doing the thermostat, I always use the universal joint piece to make it easier to tighten / loosen the bolt. But when going to put it back in, it always falls off a gabilion times before I actually get it to go in. I put some RTV sealer on the bolt first to make it stick to the socket and it made it a LOT easier! Hope this helps someone!

Thanks everyone for your help.

 

[shamaal]

Thanks for the followup, it helps to know when aproblem is fixed!