Ah nice diagram, that makes it a bit easier to trace. So does the Aux pump impede flow at all when unpowered? Does it have a stepped voltage input that drops to a lower value after 1500 rpm perhaps? Cam

2011 TDV8 Vogue in Stornoway Grey

I have disconnected the coolant valves wiring ( As they remain open). This gives good heat flow with the Aux pump & Nothing above 1500 rpm. With the aux unplugged, the flow is minimal & low temperature, hence my next move.

Last edited by Highroller on 17th Jan 2023 9:35pm. Edited 1 time in total

I've got a 2011 TDV8 but see no reason why this same issue couldn't occur on any other engines also.

I had a similar issue - sometimes the car heating would work fine and others I could set it to 28 degrees and it get no warmer than about 19 degrees. It too was linked with engine revs. In summer months I had the reverse problem - the car could get too hot, but a burst of revs would kick the air con in.

The cause was in fact my air con compressor. Replacing it solved both of these problems. Something to investigate. 2015 Range Rover Autobiography 4.4 SDV8

That's interesting Gary. What was the issue with the compressor & did your air con work?

The issue was the pressure release/control valve on the air con compressor.

The air con for cooling worked, but would stop sometimes. Raising the revs caused it to kick in again. 2015 Range Rover Autobiography 4.4 SDV8

Does it instantly go cold when you go above 1500rpm, or does it fade to being cold.

Does the engine temp drop when you sustain speed above 50 ( like when on a motorway ).

The only thing I don't read mentioned is the main engine thermostat which could be stuck open, and at speed the radiator is over cooling, and above 1500rpm the flow pressure somehow changes to route more through the radiator ?

You're changing the water anyway, so may as well when you're in there. V8 or else ...

Gary, my AC works perfectly, so can’t see the compressor being the cause ( although I may stand corrected).😄

fisha, the temperature drops pretty quick, as though the valves are closing. Once you drop below 1500 rpm, you have instant heat again. IID shows one or two degrees drop at motorway speed. Changed the thermostat twice & the only other one that I’m aware of is in the Oil mixer control valve, which I will change with all the hoses. Is there another one???

How is it going with this 1 ?? I'm about to flush the heater matrix in my new to us D3 v8 the passenger side heat is almost non existent. Iv not read that you have tried this yet

Hi Dave, I've left it alone at the moment, as I have some heat & awaiting a little warmer weather .

I flushed my heater matrix fully some time ago & had a nice flow from both sides.

Just found a battery drain on the interior fan, so currently rectifinying that. Thought it was the FSR (changed that & still had the drain), So put the old one back in. Removed the sensing fan feed on the ACT to shut the fan off & bingo!.

I now have a new water pump & purchased a complete new hose kit from Island 4x4. I will be also replacing the OMCV at the same time.
If this doesn't cure it, then I'm unsure what will, as I would have replaced the complete system by then Cheers Paul.

Well good luck with it they do try our patience

UPDATE - Still the same after loads of work & parts. I thnk that it's defeted me

Okay, So I decided to replace the water pump, Hoses, aux belts & AC Compressor & still the same.

Heater works fine - until you increase the revs or drive down the Motorway, then it blows cold. I removed the plenum chamber & blanked it off, just to see if the air was forcing by, but still the same.
Even tried wiring a switch direct to the Auxiliary water pump to see if that would work, but nothing.

I'm thinking that there is a blockage somewhere in the block, thats restricting the flow at the higher pressure (I've had most of it apart & flushed everything).

My last resort is to remove the thermostat & allow full flow. This is currently working fine & warms up quickly, Removing will it will take longer to warm up & will give full pressure to the complete system. (may have to disconnect the control valve wiring), Allowing the valves to be open all the time.

Any thoughts about this?.

You will be fine running no stat it will give full flow around the rad tho so not sure you will achieve what your looking for but nothing to loose. You will get full flow and leave the aux valves unplugged like you say

I did just recently flush my heater matrix with a flush gun both water and compressed air and its solved my issue with hardly any heat passenger side. I know you have flushed it but was it just with a hose or flush gun ?

Click image to enlarge

Only flushed with mains pressure, but had good flow. The heat at idle / low revs- speed is very good though.

I'll try without the stat, But I also have reservations. It's just so baffling why it goes cold at speed & then returns hot again as soon at the engine revs drop

There’s nothing I can add to this other than to say it’s an incredibly unusual fault.

I remember reading somewhere that on the Supercharged there’s a thermostat in one of the bottom hoses but I’ve not seen it whilst doing all the work on mine.

David. 2002 4.6 Vogue SE - Alveston Red with Lightstone Leather
2012 Range Rover 5.0 SC Autobiography in Indus Silver with Jet/Ivory Interior
2012 Range Rover 4.4 TDV8 Autobiography in Baltic Blue with Sand Interior

David, You are correct. It's one of the bottom hoses that feed coolant around the oil coolers (Oil mixer Control valve). I've changed that & bled it.
To be honest there was nothing wrong with this or the water pump when removed