Gs450H Heating Goes Cool When Engine Shuts Off (Driving/slowing Down)

[coneybiller]

Hi all, yet another issue I seem to be having with my 450h. Noticed
the other day on a local run to the shops that the heating was taking a
while to get warm, as its usually pretty quick to heat up!

Had a play around and noticed that the heat from the vents went
cooler when slowing down and the engine cuts off(Battery mode), then if I
give it some stick and the engine cuts in again, the heat comes back!
After a while of driving though it seems to stay warm all the time!

Pretty terrified about another massive repair bill I cant really afford at the mo!

Oh and the temp guage never goes above half way and the coolant level hasnt moved! I've not had the coolant changed since owning the car, but last time I visited Osaka toyota/lexus specialist, I had them check it and they said that it was fine on the protection front and that it doesnt need changing!

[TeesLS460]

Did you turn off the AC?

[coneybiller]

Umm not that I'm aware of but having it set at 26degrees and it blow cold air at me when in Battery mode shouldn't make any difference surely?

[TeesLS460]

Agreed - I have have some issues with heating when turning off the AC, but what you describe in post 3 clearly indicates a fault.

[coneybiller]

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 beenreached 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! :(

[Dracoro]

In case of an electronic issue, you could try disconnecting the Battery for 15 minutes and seeing if that resets things. Probably won't work but is a free/easy fix if it does.

[coneybiller]

I've actually got the toyota techstream on my laptop to have a look at the faults and play around. Problem is, my laptop Battery doesnt last any longer than 10mins, so I need an extension cable to run outside the house, but this time of year I dont want to chance the extension cable in the rain/puddles

[Evil Nuts]

Does the car have ECO mode??? If it's like the Auris and Prius ECO mode shuts down the PTC heater in the matrix so when the engine isnt isnt running the coolant cools.

In normal and power modes this doesn't happen.

Apologises if the info I've given doesn't help, I'm unfamilar with the Lexus Hybrid features but I work at a Toyota dealer and am fairly sure the systems are the same.

Chris

[coneybiller]

Just had a look as wasn't sure, but no eco mode that I can see, it has an auto feature that regulates the temp on its own and an auto circulation control.

If i start the car up for 10 mins and leave it idleing, the temp guage reaches halway and stops, but even if I set the temp to "HI" and put the demister on it still blows cold until you hit the accelorator, then hot air comes through, let go of the accelorator and after a few secs it then blows cold air! :(

[noby76]

heater fan blows air from a warm/hot engine so am guessing once your ECU shuts off the engine to run the car off batteries during low speeds, this might expalin why you start getting cold air blowing as engine is no longer running to generate heat for the fan to channel into the cabin.

[coneybiller]

Yea the car shuts the engine off and an electric water pump circulates the coolant when the engines off, not sure if it circulates the coolant via the heater matrix, but when the coolant temperature drops below a certain temp it then starts the engine up again! You should b able to start the car from cold, put temp to hi and windscreen blower on and it'll blow out hot air as soon as the engine has warmed up, then it'll cut the engine out and into Battery mode and then once the coolant temp drops or the batteries run low, it'll start the engine back up again therefore maintaining a constant temperature! It'll continue this cycle until you drive away!

Problem is mine doesn't blow warm air at all until you press the accelerator! Then it's as warm as it should be but goes cool as soon as you let it idle or into Battery mode! :(

[tonyricha]

Deffo something amiss with this, mine has never blown cold in 6 years of running it. I admit not so quick to start warming in the mornings unless set to windscreen but then perfect all day. My last 2 miles home thru my village I can normally achieve on the batteries only by using cruise control set at 30 but still blowing hot air at arrival.

[coneybiller]

Think I'm going to have to bite the bullet and visit my local Lexus Dealer! Not what I had hoped the outcome would be but hey ho! Was hoping someone on here or our american cousins over at clublexus would say "oh yea, I've had that problem with mine and it's X" but unfortunately no luck in that department hehe! I'm going to bet on the engine waterpump myself! Might get them to diagnose it and I'll do it myself! Theres a tutorial on how to change the pump on the GS350 on the american forum! 2 hours work tops!

[coneybiller]

Think I've found the source of the problem!! I Sarted the car up at work yesterday from cold and let it idle and come up to temp. Sure enough the temp gauge rises and still the heating doesnt get warm. Thought I'd double check the heater matrix hoses in the engine bay, 1 was scolding hot and the other stone cold (still blowing cold in car). So i hit the accelerator and waited for warm air to come through, then quickly went round and felt the pipes. The cold pipe was now hot, I stayed round by the pipes and let the engine idle again for a while and the pipe eventually got cooler and the air in the cabin grew cooler with the pipe

This suggests that the heater matrix is partially blocked and that when the engine is revved, the water pump turning faster is forcing coolant through it and making it hot! Hopefully I can fix it with the garden hosepipe by taking the two matrix pipes off under the bonnet and flushing it through backwards to dislodge the blockage!

It may have to wait until the weekend though!!!

[coneybiller]

UPDATE

Pulled off the heater matrix hoses yesterday, (cutting my hand in the process ) I ran a hosepipe through the matrix, backwards first in an attempt to clear out any debris or blockages on the inlet side and it ran clear and straight through. Ran i through the correct way round and again no restriction or blockages and ran clear straight away.

I took the cap off of the thermostat housing (while cold) and noticed there was no coolant in it whatsoever. So I re-fitted the matrix hoses (really really easy to take off and run a garden hose through BTW) and started her up, it belched a small amount of coolant then immediately went dry again, so i topped it up (with water) till overflowing, put cap back on and squeezed the top rad pipe for 10secs or so, cautiously removed thermostat cap again to find it empty, so topped up and repeated hose squeezing until, when I opened the cap it decided it was gonna go everywhere (system full) to which i stopped!

My heating's been blowing hot ever since, so it must of been an air-lock in the coolant system causing a bubble of air to be trapped inside the heater matrix pipes which seem to be the highest point in the cooling system! So there you have it, hopefully if anyone else has this issue then this could be a fix for you

[cruisermark]

well done for getting it sorted

miles of smiles and it didn't cost anything too

[deighty]

Thanks mate, this was exactly the problem I had and your postings sorted it out for me. You saved me a bundle in Lexus Woodford fees, who, by the way are useless and probably would've ripped me off for such an easy fix.

[Double D]

Same problem, same solution.

Removed engine cover, undid cap, no liquid. Poured in just over pint to fill, recapped, ran engine for a minute, rechecked level, then ran engine up to temperature. Heater came on and stayed on. Drove round town for ten minutes, heater didn’t cut out at all. 😊😊😊

[Steven Lockey]

On 2/12/2014 at 5:02 PM, coneybiller said:

I've actually got the toyota techstream on my laptop to have a look at the faults and play around. Problem is, my laptop battery doesnt last any longer than 10mins, so I need an extension cable to run outside the house, but this time of year I dont want to chance the extension cable in the rain/puddles

Why does that matter? Unless you are daisy chaining extensions, then just keep both ends in the dry, you can dip the cable in all the water you want unless its full of holes in the insulator! (in which case throw the damm thing away and get a new one anyway)

 

 

[Britprius]

I am happy that the OP seems to have found a solution to the problem, but there is another item that can cause this problem that unless I have overlooked it has not been mentioned. The item concerned is an electric pump that circulates the engine coolant around the heater circuit when the engine is not running. This allows the heat to be removed from the engine, and passed round to the heater when the engine is not running.
All the hybrids have such a pump mounted somewhere. In the GS it is mounted on the drivers side inner wing, and can be herd running if you put a long rod or screw driver against it stethoscope style after the engine has shut down automatically.
Do not confuse this pump with electric pump that circulates a separate  coolant circuit to the inverter, and transmission.

John.