Replaced thermostat- no heat, perfect engine temp

[TisMe]

Howdy folks,

pretty simple question but illusive answer. I got a fresh thermostat housing (with everything preinstalled) for my dad's 2004 XC70. I installed this in the wintertime since then, engine temp is perfectly at 12 o'clock, but when I activate the heat it's lukewarm at best.

I've searched for answers on this, but come up short. The heat was working fine before the maintenance, and since engine temp is good I'm not worried. But, it's springtime and I'm ready for a resolution.

Thanks!

[vtl]

In no particular order:

- air bubble trapped in the heat core
- heat core is clogged
- HVAC air distributor malfunctions (common at this age)

[jonesg]

I did this job 3 months ago when it was too cold to ignore.
The housing came with therm' and new temp sensor, it was no good.
The bad new sensor ran the cooling fans and prevented the engine from reaching op' temps around 185, the fan kept the temp at 155F tops.
Reinstalled the old original sensor and ordered OEM volvo, all good now.

Did you ensure the pintle bleed valve on the thermostat is at the top or highest point, to let the air pocket in the housing to vent.

[dikidera]

Just so you know, Volvo use a smoothed value for coolant temp. The needle on the odometer may be perfectly vertical at 60c-70c, way before working temp. Meaning a stuck thermostat.

But, I have had this happen to me when I replaced the heater core. I had to wait for the car open the thermostat several times with an open coolant cap to get out the air pocket. Otherwise I had no heater.

[TisMe]

I did this job 3 months ago when it was too cold to ignore.
The housing came with therm' and new temp sensor, it was no good.
The bad new sensor ran the cooling fans and prevented the engine from reaching op' temps around 185, the fan kept the temp at 155F tops.
Reinstalled the old original sensor and ordered OEM volvo, all good now.

Did you ensure the pintle bleed valve on the thermostat is at the top or highest point, to let the air pocket in the housing to vent.

So it's possible I should badger FCP about a replacement unit?

It's funny you mention the bleed valve... my first attempt, I cracked open the housing and installed just a new thermostat. This got me full heat, but the gauge readings were wonky, literally hunting, so I didn't trust that I got the therm seated aaand would prefer the only time I blow an engine to remain in my night terrors.

I decided to bite the bullet and get the full housing, with preinstalled therm and sensor. That eliminated potential user error regarding the pintle bleed valve. Figured this would solve all, but here I am.

Oh, and I just bundled up an extra lot on the days that the roads would slide my RWD e30 off the road I felt bad when my sister-in-law had to borrow it, but she's a trooper.

Just so you know, Volvo use a smoothed value for coolant temp. The needle on the odometer may be perfectly vertical at 60c-70c, way before working temp. Meaning a stuck thermostat.

But, I have had this happen to me when I replaced the heater core. I had to wait for the car open the thermostat several times with an open coolant cap to get out the air pocket. Otherwise I had no heater.

That's a pro tip about the "smoothed value", thanks. Unless Murphy's law is in full effect right now, my brand new thermostat unit should be good, and my heater core should not have magically combusted the moment I did this work.

I'm definitely going to go for ANOTHER burping procedure before I rip this beast apart again. I'm tired of dumping coolant, I can only save so much of it. On second thought, I do have too many cats...

[dikidera]

Dumping? To burp the car you don't need to drain anything. And yes, the coolant value is smoothed. The needle is full vertical well before operating temp and stays there up to 125c engine temp.

[TisMe]

Dumping? To burp the car you don't need to drain anything. And yes, the coolant value is smoothed. The needle is full vertical well before operating temp and stays there up to 125c engine temp.

"Dumping" in reference to if I were to remove the thermostat housing again.

Thanks again for the knowledge! I usually trust Volvo, but in this case...

[XC70Rider]

When I replaced the thermostat with a full coolant flush it took several valve openings to burp all the air out. I had the front end raised on ramps and used the Lislie Spill Free Funnel. That funnel is great for burping air and comes with adapters to fit nearly any radiator.

[jonesg]

Grab the heater hoses at the firewall, if they are hot when engine is up to temp its not the thermostat, its the plenum door actuators in the dash.

[vtl]

I just drive around with a jug of diluted coolant and top up when the low coolant messages comes in. Does not take longer than 20-30 minutes.