Slow = Cold air

Steven Lockey · October 10, 2023

Before I start digging about thought I would ask here.

Basically the issue is, when I'm driving slowly (sub-50), I basically get no cabin heat bar the heated seats. Vents just blow cold, even if the temp is set
to maximum (I thought it might be a sensor problem but seems not).

But it works fine if I'm going 50+ and comes on if for example I'm going up a hill or constantly accelerating hard at lower speeds.

Now this all leads to their not being enough engine heat to transmit.... but the thing is, its like 30+ minutes before the heat
kicks in below 50 (and often goes cold again).

Engine temp on dash rises normally to half-way point before stopping as you'd expect so nothing abnormal there. It's up to the normal
level and sitting there regardless if the air-vents are blowing cool or hot.

Only sane explanation I can think of is the heat-exchanger isn't connected to the air-vent properly so engine has to be particually hot to
actually transfer heat.

Any other ideas or where to look for the heat exchanger on a GS450h (pre-facelift) would be appreciated.

Steven Lockey · October 10, 2023

Nevermind, think I found the answer from 8 years ago on this very forum. Also a post I commented on 3 years ago before I had this issue 😉

Looks like it maybe a air-lock in the heating matrix and just needs running with the cap open and refilling with coolant.

Steven Lockey · October 14, 2023

Coolant system bleed, feet now warm again 🙂

hazelnut · October 18, 2023

Our 2009 GS450h just developed this issue today. I guess you and I must have a leak for this to happen ?

KayCee · October 19, 2023

if its Ok for me to comment this is usualy caused by the water pump developing a leak if you can see pink crusty stuff aroind and under pump thats the problem.

hazelnut · October 19, 2023

On 10/10/2023 at 4:35 AM, Steven Lockey said:

Nevermind, think I found the answer from 8 years ago on this very forum. Also a post I commented on 3 years ago before I had this issue 😉

Looks like it maybe a air-lock in the heating matrix and just needs running with the cap open and refilling with coolant.

So what is the bleed procedure? I just put 2 litres of genuine Lexus premix coolant in, started the car for a few minutes and the heater started warming the cabin. stopped the car, add more coolant, repeated this a couple of times, but feels like I could be doing this all day and topping up. I can't see any leaks, but now I discover the car did overheat some days ago.

hazelnut · October 20, 2023

I found this on YT:

I've got this thingy on order :

https://www.amazon.co.uk/gp/product/B01A2CQSU6

So I should be able to bleed with this. .. I hope ..

Steven Lockey · October 20, 2023

On 10/19/2023 at 10:32 AM, hazelnut said:

So what is the bleed procedure? I just put 2 litres of genuine Lexus premix coolant in, started the car for a few minutes and the heater started warming the cabin. stopped the car, add more coolant, repeated this a couple of times, but feels like I could be doing this all day and topping up. I can't see any leaks, but now I discover the car did overheat some days ago.

For someone as inept as me, procedure was call garage, arrange time, drive in, wait 1 hour, drive home warm 😉

I looked at doing it myself but the garage only wanted £70 to do it so by the time I brought everything and messed about wasn't worth it for the £20 or so I'd save.

hazelnut · October 22, 2023

I did the 'no-spill' funnel coolant bleed today - amazing really is no-spill.

hazelnut · November 29, 2023

I've been using this funnel a lot lately. I'd rather fix the leak but I can't find it. Is there a cunning way to add pressure to the system when cold ?

johnatg · November 30, 2023

Here's a video of how it's done.

But I'm afraid - if you can't see the leak from outside the engine, the coolant is likely to be going inside - ie into a cylinder via a head gasket. Hopefully it's not that.

Steven Lockey · November 30, 2023

Should see signs of that in the oil if its leaking into the engine.

johnatg · November 30, 2023

Not if it's going directly from a water passage to a cylinder. You only get water in the oil if there's a leak between an oil passage and a water passage.

If there's no leak into an oil passage but there is to a cylinder the water will just get vapourised and blown out of the exhaust.

Water leaking into a cylinder actually improves combustion....for a while.

My supercharged MX-5 has water injection - it's there to act as an intercooler but it keeps the cylinders nice and clean!

johnatg · November 30, 2023

PS - Hazel - if you have or can get hold of an endoscope you might be able to find a clean cylinder by looking through a plug hole - might save having to remove one cylinder head.

But again - I hope it's not that - removing a head on these engines is a real task!

Mention of a recent overheating problem doesn't bode well though.

Steven Lockey · December 1, 2023

True, but its less of an issue if its going into the water since the coolant fluid tends to turn into a horrible
sludge when combined with oil and high temperatures.

And engines don't like being lubricated by sludge 😉

Might cause some issues with the cats through.

hazelnut · December 2, 2023

Thanks guys. I've bought this draper pressure test set.

Sealey VS0013 Cooling System Pressure Test Kit 10pc | eBay

I have an entire spare car to swap parts over, so I am hoping it is either the radiator / pump or cap. I have previously had a car with an annoying slow leak that was really hard to spot. Turned out to be the radiator, I only found it by getting the car really hot so the coolant was pressurised.

KayCee · December 2, 2023

Hazel

Have a look under your waterpump and see if you can See any Pink crud under the Pump my MK3 a few years ago Had exact same problem and it was the water pump leaking I dont think your Head Gasket as gone.

You may need one of those small mirror type Pens to see it but i will wager its that

I had 2 mk3s from 2010 to 2013 and i had to change both pumps (well lexus did)

but they changed design after MY 2010

If you look on the US site its full of Problems with water pumps on the Mk 3

Robert

hazelnut · December 2, 2023

I braved the cold and hooked up the new toy, pumped it up to 10psi, then came back 5 mins later - still at 10psi. While there I swapped the cap as I could hear wheezing while I squeezed the top hose. Still had the wheezing with the alternate cap. No crusty under the water pump, and no obvious leaks anyplace.