Lukewarm heat. (New Rad. & Heater core)

TLDR. New rad, new core, flushed and burped - no heat. Maybe water pump?

So I’ve got an 02 V6 with 220K miles on it now. Didn’t have heat last winter, so I had brought it in and they said the heater core was bad.

I replaced the heater core, flushed the system as well as flushed and back flushed the new core itself. Still - No heat when the fan was on high (worked on low-med).

I noticed the radiator Was rotted and rusting, so me and some friends flushed and drained the system (and same procedure with heater core), put in a new radiator, and now heat works on high, but at idle it blows warm but not HOT.

When driving, even at low RPMS like 1200-1500 it gets really hot, I have a thermometer that reads 95 at idle, 135 at 1500 RPM.

Is this normal? I’ve tried everything. I’ve burped the thing a million times at this point as well as checked coolant levels.

Inlet hose to core is HOT outlet is WARM/LUKEWARM (I presume that’s normal). Temp outside is about 32 here in detroit.



My heater control valve to the core IS chipped where the hose connects but from what I can tell it is not losing coolant, nor has the piece gotten lodged into the new core (was chipped before replacement).

Driving on a long drive the other day it went cold until I turned off and restarted the truck and the heat was hot again.

All I can think of is MORE AIR, possible water pump failure (it’s factory pump still), or I read a head gasket leaking could cause this- Although the head gasket was replaced a mere 60K miles ago by a dealer.

EDIT: no air comes bubbling up when burping radiator, and to burp radiator I have front end of truck raised about 6” driven up on some 6x6 wood railroad pieces.

 

Could possibly an issue with the electronics behind the temp selector, the blend door actuator, or even the cable connecting to the valve in the engine bay.

Check to see that when you change the temp dial, that the cable in the engine bay moves. Then move back to the blend door actuator. Then back to the climate control module.

 

What he said.....there's not much else......

 

Okay. I’ll try this tomorrow I’ll check back as soon as I test it. Thanks for the response.

 

So the issue is the heater only blows hot while driving, only blows warm while at idle, and it sometimes goes cold while driving?

If the engine isn't overheating then I wouldn't suspect water pump is faulty. Do you have an OBDII scan gage to read the coolant temperature?

If the inlet to the heater control valve is hot and the outlet from the heater control valve isn't hot, that would imply the heater control valve is faulty. That's what I would check.

 

I would also agree with this- especially considering the OP mentioned the water pump might be original and 220k old. Either way, sounds like both the timing belt and water pump are up for replacement.

 

I do actually have an UltraGauge. Coolant temp heats up to 195 and never gets above that. When driving it goes between 185-195.

 

That heater control valve seems fairly simple and cheap. I’ll check out the electronics in the morning and if they check out and work I’ll run up and grab a new control valve and slap it on. Thanks for all the replies so far.

 

Hey all I won’t be checking that stuff out today. Just got back from the urgent care with some pretty intense symptoms. I’ll check in here with what I find as soon as I’m ship shape.

 

Okay all. I have replaced the heater control valve, it actuated correctly and I tested the part prior to install with my hand. Like I said just a second ago the part actuated using the controls on the dash, arms move and valve opens and closes. To my surprise the heat is now ice cold, with tons of pressure in the lines that wasn’t there before. My guess is air locked core? Just spent about an hour outside attempting to burp this thing with the front end up on a parking brick, and let me tell you I send those rpm’s to the moon and tons of air came out… still no heat. Like I said it’s colder than before and yes! the old part was in fact faulty and only half opening. Any ideas?

 

Water pump IMO

 

Gonna make me cry LOL

 

Not my intent but you’ve replaced about everything you can but as some have said, sounds like faulty water pump. You honestly should perform the timing belt and water pump every 80K… faulty pump could be reeking havoc on the inside of your engine. Don’t mess around and get done. 3 things you gotta without fail every 80K, water pump/timing and LBJ

 

Yeah. I never knew about doing the pump but I had all the timing belts replaced by a shop about 30k miles ago and I did the LBJ and UBJ this last summer. I guess I'm just not understanding why the heat would have gotten colder after replacing the faulty heater control valve. I mean if it is a failing pump it should still be the same as it was with the old valve at the least right?

 

I'm no expert, but I can't get on the "water pump train" without seeing the engine temps go above normal. I'm out of ideas. It has to have something to do with that valve or perhaps a clogged line.

 

I’m going to try and reverse flow the core today and burp it again. The engine temp seems fine it’s been just chilling (not) at 195 but no over heating. Lines all have really good pressure. I noticed this morning the inlet line to the core is now COLD! That gives me hope that maybe the core is airlocked or plugged after I replaced the valve and so maybe reverse flow garden hose might be the last step!

 

The inlet line to the core, downstream of the valve? It has to be that valve... it's the only change since it was partially working.

We gotta get some pictures in this thread.

 

Maybe faulty thermostat, or it’s vapor locked

 

Hey all. Final update here. Just finished working out there with my roomates. Core was FULL of air as was the whole system. I pumped air out of the core using a harbor freight fluid pump. Then I used a no spill funnel and, added some more coolant, and sent that tach to the moon (4-5k rpm’s for a solid 5 mins at a time) tons of bubbles came out and then all the sudden they stopped, and no more bubbles surfaced for next half hour at idle, so I turned her off and let her cool down sucking in some more coolant from the funnel. Sure as sh** I put my thermometer in the vents and she was blowing at 130! I went to the gas station to top it off and was sweating! I definitely think it was the valve, cause this difference is crazy. Thanks all for the help and ideas. I’m just happy it wasn’t the water pump

 

I would send some photos but now it’s resolved. I do have an awesome video of the 3.4 soaring to the moon in my garage while being burped tho.