Heater only works when going over 60mph

19woodstock50 · Post by **19woodstock50** » 16 Dec 2017, 09:07

I have a 2004 1/2 S40. Heater blower work fine but will only blows warm air when you are travailing over 65mph. Temp gauge comes up to temp as normal. As soon as you get below 65mph it starts blowing cold. 65 and above no problem. Any clues?

Post by **jvl** » 16 Dec 2017, 10:27

Bad head gasket?
But then again, the temp gauge coming up as normal does suggest normal cooling.
Maybe clogged cooling channels or failing/slipping water pump? What about lower speeds at higher revs?

Post by **mrbrian200** » 16 Dec 2017, 10:52

My vote goes to clogged channels - most likely in the heater core itself. If the water pump were failing to such an extent as to get no flow to the heater core at lower RPMs I would expect you to see an elevated engine temperature gauge/indication when idling for more than a few minutes. If the coolant isn't OE-blue colored there's no telling what (cheap stuff that isn't appropriate for these cars) was put in there. Corrosion=particulates stirring around which in my experience the heater core will usually plug up first with the radiator to follow. There's also another possibility: a hose was replaced at some point in the past with generic non-formed hose, or one of the hoses collapsed at a bend resuling in a kink restricting flow like you'd get when you get a kink in a garden hose.

19woodstock50 · Post by **19woodstock50** » 17 Dec 2017, 06:57

jvl wrote: ↑16 Dec 2017, 10:27 Bad head gasket?
But then again, the temp gauge coming up as normal does suggest normal cooling.
Maybe clogged cooling channels or failing/slipping water pump? What about lower speeds at higher revs?

I will have to try the higher revs at a lower speed. Thanks

Post by **jvl** » 17 Dec 2017, 14:24

mrbrian200 wrote: ↑16 Dec 2017, 10:52 My vote goes to clogged channels - most likely in the heater core itself. If the water pump were failing to such an extent as to get no flow to the heater core at lower RPMs I would expect you to see an elevated engine temperature gauge/indication when idling for more than a few minutes.

Well... to my own surprise as well: I used to have a Land Rover that suffered from the impeller slipping on the water pump axle, was at the verge of failing but it wouldn't always slip. Took me a while to figure that out. Water pump replacement was easy on that car, took 2 hours.
Never done one on a Volvo, so wouldn't know about those.

But check for coolant flow at high revs amd lower speeds as well! Might indeed as well be flow restriction: non original hose or twisted hose, or maybe sludge in head?? Was any 'leakstop' used on this car??

Post by **oragex** » 17 Dec 2017, 14:36

How are the thermostat and the water pump?

19woodstock50 · Post by **19woodstock50** » 18 Dec 2017, 14:27

jvl wrote: ↑17 Dec 2017, 14:24
mrbrian200 wrote: ↑16 Dec 2017, 10:52 My vote goes to clogged channels - most likely in the heater core itself. If the water pump were failing to such an extent as to get no flow to the heater core at lower RPMs I would expect you to see an elevated engine temperature gauge/indication when idling for more than a few minutes.
Well... to my own surprise as well: I used to have a Land Rover that suffered from the impeller slipping on the water pump axle, was at the verge of failing but it wouldn't always slip. Took me a while to figure that out. Water pump replacement was easy on that car, took 2 hours.
Never done one on a Volvo, so wouldn't know about those.

But check for coolant flow at high revs amd lower speeds as well! Might indeed as well be flow restriction: non original hose or twisted hose, or maybe sludge in head?? Was any 'leakstop' used on this car??

No leak stop was used.