Heater only warm and not hot

Choppertrash · Dec 30, 2011

Hi everyone,

I have a problem with my 300tdi heater, in that it is only blowing luke warm air, and is not as hot as it was. I did the head gasket a few weeks ago, and it bled up fine, and has been blowing hot air ok.........but now its only just warm.

Does this sound like a heater matrix problem, or is it hopefully something a lot simpler to fix? Surely if there was an airlock, then I would only get stone cold air, not warm?

Any help much appreciated, as the search didn't really nail the problem. Cheers.

sierrafery · Dec 30, 2011

Check the pipes which are "feeding" the heater assy(in the engine bay) ...if they are evenly warm and at the same temp as the bottom hose of the cooling circuit then it's a matrix malfunction(some flaps is blocking the hot air's access)...if the pipes are not warm enough then it's a coolant flow issue.

discool · Dec 30, 2011

What the 'Count D' said, I could not put it better :banana:

janderson41 · Dec 30, 2011

also check or replace thermostat.Cheap and easy fix. Had a similar problem with heater taking ages to heat up then not very warm. Thermostat cured this. There have been other posts saying the same. Worth a try before having to remove matrix.
cheers
Jim A
1996 300Tdi auto(jap reimport)

Choppertrash · Dec 30, 2011

janderson41 said:
also check or replace thermostat.Cheap and easy fix. Had a similar problem with heater taking ages to heat up then not very warm. Thermostat cured this. There have been other posts saying the same. Worth a try before having to remove matrix.
cheers
Jim A
1996 300Tdi auto(jap reimport)

I did the thermostat when I did the HG, and the new one was a genuine LR part, so that should be ok Jim (I hope), and the rad hose is hot, but cheers anyway.

I checked the pipes that go to the heater (as suggested) and of the 2 hoses, the top was hot and bottom was fairly cold. I thought I would also just check for an airlock, and the level in the header tank had dropped a bit, and I did bleed some air out of the t/stat housing.

I hadn't checked the water level for about 4 weeks/ 1000 miles............I do a 40 mile round trip a day to work, and I do put my foot down a bit, so hoping the water loss is just a maintenance thing.........there are no visible leaks, or any odd engine things, so fingers crossed.

Thanks for the help chaps

discool · Dec 30, 2011

I've never checked if it's true but I have always understood that the supply to the matrix was the bottom hose therefore would be the hottest although the other hose would still be hot.

Choppertrash · Jan 3, 2012

discool said:
I've never checked if it's true but I have always understood that the supply to the matrix was the bottom hose therefore would be the hottest although the other hose would still be hot.

I'm still getting the same problem..........Only luke warm air from the heater, and sometimes its even cooler when cranked round to hot .

The top hose that goes in through the bulkhead is hot......this one comes from the top of the head. The bottom hose going into the b/head is cold.......this one joins into the metal pipe which runs along side the inlet manifold and then joins into the water pump hose. That hose is cold all the way back to the pump. Is this how it should be?

System all bled up, no visible leaks, no overheating. Does this sound definately like the matrix?

sierrafery · Jan 3, 2012

On working temperature all the pipes/components must be the same... IMO your heater rad is clogged. Clamp the two supply pipes to it as to not lose much coolant then run some water through it to see if it passes or not(try to attach a proper pipe and fill it starting from the bottom)

Choppertrash · Jan 3, 2012

sierrafery said:
On working temperature all the pipes/components must be the same... IMO your heater rad is clogged. Clamp the two supply pipes to it as to not lose much coolant then run some water through it to see if it passes or not(try to attach a proper pipe and fill it starting from the bottom)

I take it by that, you mean the actual heater rad inside the cab? So you mean clamp and disconnect the 2 pipes, and run hosepipe into heater at bulkhead?.......and hope for a good flow out? Sorry if I made myself sound thick there. :doh:

sierrafery · Jan 3, 2012

I meant clamp and disconnect heater assy then attach hose to the bottom pipe of it and wait to see if the water comes out easyly through the upper pipe....cos if not then this one is clogged and it's the reason for your problems

ScottJones1 · Dec 18, 2017

Hi all I’ve replaced the heater motor on my discovery 200tdi now mine are only luke warm not hot. All the pipes get hot and the temp gauage goes to half way. Could someone help me out? Does the system need bleeding? Or is it the thermostat?

Heater only warm and not hot

Choppertrash

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