Speedy0o

Hi all, my '06 GS450h has developed a fault where the heater blows cold at idle and low revs but blows warm when driving or revving the engine at a standstill. The coolant hasn't dropped at all and the car never goes above halfway on the temp gauge. Its starting to get frustrating now the cold weather has set in and temps dropping! Long journeys are ok as at high speeds it stays warm but short journeys are uncomfortable!

I just had a feel of the rad hoses and hoses that go into the matrix (engine side of bulk head) and matrix hoses feel warm (both of them), the top hose to the rad is warm but not hot and bottom hose is cold suggesting the stat hasn't opened yet. Its cold outside so getting the car up to temp is quite difficult without a long drive (rush hour at the mo).

Still I just had the car parked on the drive and cranked the heater up to max and held the accelorator for a while and super warm air blows out. The engine cuts back out as "normal operating temp" has been reached for battery mode and then the heater goes cool again! Still the bottom radiator hose is cool and top hose not massively warm. It has never overheated thus far and I drive 150miles a day back and forth to Reading from Cheltenham 4 nights a week.

Only thing I can think of is a sticky thermostat or waterpump not operating sufficiently enough to circulate the water?!?

Anyone got any other ideas? Its getting colder and short trips where it used to blow warm air nice and quickly (within 3-5miles) are becomming unpleasant!

twylie

iTrader: (3)

thermostat stuck/broken open is most likely culprit if the temp gauge is reading normal.

Speedy0o

would that explain the heating going cool when the engines idling and hot when the engine revs pick up?

twylie

iTrader: (3)

Likely. It could also be some kind of blockage on the heater core and at higher RPM, the water pump is circulating more coolant through the system, but my bet is the T-stat. I'm not sure on the GS, but replacing the thermostat on most cars is relatively easy and not terribly expensive. The part is probably no more $30-50, even from Lexus. Normally the top hose will be HOT to the touch when at operating temps.

I'm not sure how the heating system works on the hybrid. Once the engine cuts out, there is not hot coolant circulating through the heater core.

May want to post on the hybrid sub-forum as it could be expected behavior unless there is an aux heat system that engages when on battery.

Post back once you get it sorted.

Speedy0o

I did post on the hybrid section but thought I'd post on here due to sharing the same 2gr engine as the 350. It does have a secondary electric pump but I should of thought it would throw a code if that was playing up! Thermostat does sound plausable then, I've just done a 75mile trip to work and checked the matrix pipes, both seem hot enough, top rad pipe was scolding hot and bottom pipe was slightly warm but not in any way hot, either the rad is super efficient or the stats not opening fully perhaps? I no the bottom pipe should b cooler but surely not to the point where it's almost cold???

twylie

iTrader: (3)

is it only when on battery that it's doing it? Can you do a low speed drive that is just fast enough to keep the engine running, but at low RPM? That may give you a better indicator if the aux pump isn't working properly. Given that the car isn't overheating, it may not throw a code if there is an problem somewhere since it's not a critical function in terms of hurting the car or other damage. If you can find a full service manual, there may be a procedure to test the aux pump function.

The radiator in my GS430 must be pretty impressive. I had to drive the car in a snow storm a few years back and between crawling at low speed for hours and having half the grill covered in ice and snow, I was very impressed the car didn't show any signs of overheating or otherwise acting up.

Good luck as I've dealt with a lack of a heater in the winter and it's no fun.

Speedy0o

It seems to do it at lower revs as well as on battery mode! I believe the auxiliary pump serves to circulate coolant to the HV inverter to keep that cool during battery driving. When the cars in battery mode it keeps an eye on the coolant temperature (presumably) and will cut the engine back in if it drops. It must work off of engine coolant temperature though as it'll still cut out even though its cold in the cabin! I would of said the aux pump was working though as if that had failed then surely the inverter would fail or overheat! Would of thought there would be some sort of overheat protection for it just in case!

I did notice that it blew cold air out again after my 75miles journey and stopping at a petrol station for 5 mins and driving off again, could a diverter flap or something along those lines in the heater box cause the flow of air to be moved away from the matrix? Although saying that, it wouldnt explain why it gets hot again on acceleration! hmphhh