Can a bad heater control valve cause overheating? I know it may sound dumb but going to work this morning, I had heat running and truck proceeded to go all the way to the red pulled over shut off for 15 mins started back up and ran fine and stayed at half. Driving home, didn't turn heat on, heated to half way and never moved.
Thoughts?

 

Mine does this as well. It gets close to the red zone, but if I keep driving it it slowly goes back down. Curious to what this is!

 

No, if anything it would reduce heat (more heat being transferred to air via the heater core). Unless your heater core has a massive coolant leak but you would've noticed that!

Sounds like you might have air in your coolant system. Bubbles will tend to hang out at the coolant temp sensor causing a false reading. Don't assume it's that though if it overheats again.

 

yeah I hope it's just a bubble. this weekend was the first time it sat and didn't get started since we got the air out before.

 

In your case, it sound like more of a bad thermostat. It's not opening fast enough (or an aftermarket one at the wrong temperature range) causing the engine to overheat until it finally does open. Not a sure fire diagnosis, but likely. You'll want to get that fixed, long term overheating will blow your head gasket, guarenteed.

 

I ordered the dual thermostat and a new heater control valve for $100 from the dealer for both. should be here by Thursday.

 

Oh... well the one's from Autozone work great... I've used them twice now and they are like $17...

 

Actually his problem does make sense. Not all yotas have this issue BUT some do. When your heater is on it is dissipating more heat, the cooler fluid coming from the heater core gets dumped out right at the thermostat. If it is to cold the thermostat wont open. I believe 4crawler has a little write up on the issue.

 

ran no heat all day today and no issues! pretty f'n cold in MN right now though so hopefully this valve gets here soon!

 

Did that take care of your problem? I ordered a new thermostat also with the little "bypass" valve on it. Mine was doing the same thing, my idle was also surging..

 

Surging idle means low coolant, or air in the system. It can also happen when your coolant freezes, OR you have a bad ect senesor. This happened to me when we got down below 0*F a few weeks ago. Went out to warm up the truck, come back out 5 min later, and the idle was surging, no heat coming from the heater. I then remembered that I had a leak over the summer, and filled up with water after repairing the leak, and never put any antifreeze in... DOH!!

 

heater control valve took care of overheating problem. I have a Weber installed that till needs to be tuned again after moving from 15000 ft to 500 ft. I also installed the yota thermostat, so either valve and/or thermostat solved the problem. It still isn't full heat I don't think but its much better than none!