940 SE, non-ac, how hot should the heater be?

[Laird Scooby]

Originally Posted by kiloran

Aha - that has to be one of the stranger quirks I've encountered. Can't recall any of the 15+ cars I've owned delivering cold air from some vents whilst others are delivering hot.

Further diagnostics - passenger side outer vent is warmer than the driver's side outer vent. And the glovebox is noticeably warm based on the slightly melted Twix I found this morning

Still waiting for stat to arrive.

That's the standard set-up on most 7/940s with manual heating and no air-con, centre vents are fresh air, outer vents go through the heater so can be simply fresh air or heated. Fan assistance is available on all though.

If you use the screen demist function on the heater, you'll also find the passenger side clears quicker than the drivers side. Never worked out why but have noticed the same on almost every car i've ever owned, regardless of make.

The heater ducting for the outer vent is behind the glovebox and to the right is the heater box so no surprise you have a iTwx instead of a Twix!

[kiloran]

A brief update - Ciara prevented any work at the weekend so I haven't done the stat yet.

Elsewhere there was mention of checking the viscous fan coupling - there seems to be no difference in (physical) resistance of this whether hot or cold. After the usual school run (40 minutes of driving at around 30mph) with temp up to its usual 11pm-ish position it's easy to spin by hand.

Cabin remains lukewarm but the good news is that I don't see/feel any moisture coming from the HCV so I think we can rule that out. Will aim to do a full coolant flush and change the stat at the weekend, weather permitting.

[Laird Scooby]

Originally Posted by kiloran

A brief update - Ciara prevented any work at the weekend so I haven't done the stat yet.

Elsewhere there was mention of checking the viscous fan coupling - there seems to be no difference in (physical) resistance of this whether hot or cold. After the usual school run (40 minutes of driving at around 30mph) with temp up to its usual 11pm-ish position it's easy to spin by hand.

Cabin remains lukewarm but the good news is that I don't see/feel any moisture coming from the HCV so I think we can rule that out. Will aim to do a full coolant flush and change the stat at the weekend, weather permitting.

It was me mentioned checking the vicious fan coupling, sounds as if it's playing the game by the rules so all good there.

Try swapping the heater hoses at the bulkhead connections, if you get the Jubilee clips loose (seem to recall you lubed them some days back) and ensure the hoses are free to move on the stubs you should be able to literally swap them in seconds minimising the coolant loss. If that improves the heater output then you've solved half the problem. If it reduces the output, swap them back.

[TonyS9]

Originally Posted by Laird Scooby

That's the standard set-up on most 7/940s with manual heating and no air-con, centre vents are fresh air, outer vents go through the heater so can be simply fresh air or heated.

Yeah, 300 series is the same, just close the centre vents during the winter.

Dave, do you know which is the correct way around? Pump (red pipe) connects to lower hose with the control valve?

[Laird Scooby]

Originally Posted by TonyS9

Yeah, 300 series is the same, just close the centre vents during the winter.

Dave, do you know which is the correct way around? Pump (red pipe) connects to lower hose with the control valve?

I've always worked on the idea the feed/cylinder head hose is the top and the return (to water pump) is the bottom one Tony. For some reason on some cars it makes no difference, on others it makes all the difference. My Jeep Cherokke was the same, some idiot had fitted an LPG vapouriser in parallel before the heater valve and crossed the pipes after the vapouoriser and the heater was stone cold (even in the middle of summer!), swapped them back and it was lovely and warm. What didn't help was the vap was mounted so high it was prone to air locks and would ice up on tickever on a hot day on gas, even worse going uphill in the middle of winter with 2 tonnes of car and trailer on the back end!
Had to switch back to petrol on a few hills until i eventually had time to trace the problem.

[TonyS9]

Yep, mine seems to be head connected to the bottom one. Its not bad, I just assumed the it was slower to warm up than the 360 due to size.

[bob12]

Originally Posted by Laird Scooby

That's the standard set-up on most 7/940s with manual heating and no air-con, centre vents are fresh air, outer vents go through the heater so can be simply fresh air or heated. Fan assistance is available on all though. ................

You may also notice (at least on a late 745) that on the 'standard' set-up the more you increase the heat the less air comes out of the central vents.

[kiloran]

To close off this thread, replacing the thermostat has sorted it. The car had an 88 degree stat in it, the correct replacement part was a 91 degree, and a lo and behold the temp gauge is slap bang in the middle now (previously sitting around half 11) and the heater is furnace-like. Will bode well for the winter

[Laird Scooby]

Originally Posted by kiloran

To close off this thread, replacing the thermostat has sorted it. The car had an 88 degree stat in it, the correct replacement part was a 91 degree, and a lo and behold the temp gauge is slap bang in the middle now (previously sitting around half 11) and the heater is furnace-like. Will bode well for the winter

Good news, well done! I suspect the 88C 'stat had gone weak with age, those 3C won't make a wild amount of difference to either the gauge or the feel of it if it's working right.

However at the "half-past-eleven" position, you're probably losing 10-20C from where it should be so will make a big difference!