GarethZA

Hi,

I purchased a second used 2006 GS300 from an ex colleague when I left the company and moved on.

I've put about 5,000KM on the car, it currently has 195,000KM.

The car is/was mechanically great, until this week when I had some cooling issues..

First sign of problems was when I noticed steam bubbles in the expansion tank after the engine was turned off. I was actually filling up with oil as the oil warning light came on - 2nd time in 5000km but I guess that's normal for a car of this performance, size and age. I hadn't noticed overheating sings at this point but I remember fans being generally noisy (In SA it's in the height of summer so I didn't think much of it).

Temperature seems to be rock solid in the middle of the gauge, something I noticed as it gets very hot here and traffic is sometimes quite bad...

The next day I had been driving about 15 minutes on the motorway and I noticed the temperature gauge was suddenly in the red. I pulled over, noticed expansion was empty and filled. Decided to carry on another 5 mins as I had 2 small kids in the car and it's not a safe place to be (side of the motorway).

I finally found the radiator cap after I was recovered home and filled up with water (appeared to be very empty).

Next day little loss in expansion tank, low miles driven
Next day needed to drive out a little further, about 50KM later the temp gauge started flipping hot then in the middle, hot then middle and then the engine warning light came on and the stability control light came on!

I was carrying water so filled up quite a lot of water again and the car started up perfectly and I returned home.

Since then I've been trying to investigate the problem, I will bullet point finding...

• no obvious leaks
• no oil in water / water in oil
• no apparent general overheating (except the 2 times with water loss)
• AC and heating working perfectly
• no performance loss
• driving lightly, up to temp no steam bubbles in tank w/ engine off
• driving heavy at working temp leads to steam bubbles even when off
• replaced radiator cap - no change
• radiator cap off and engine running cold, small water movement with a light sucking/bubbling - seems like air is sucked in every 10 seconds or so (very small volume of air into a tine whirlpool then air bubbles back). This I paid attention to, it settled down when engine heated up.
• revving engine shoots water out of radiator - noticed when trying to get temperature up, I believe this is just the pump spinning up and normal?
• research leads me to believe it's not a gasket at there is no significant stream of air from cold and no huge volume of steam from exhaust.

Lexus can't look at this car for 2 weeks, I may see if I can find an independent mechanic but I'd like to get an understanding of the problem this week and find someone next week.

Many thanks for information and advice,

Gareth.

ez12a

doesn't seem that failed headgasket/burning coolant is a common issue with these cars, so i'd look more carefully for leaks to see if you have a failing water pump as it's significantly more common it seems. Mine had a badly leaking one at 90k miles.

If you look by the pulleys at the front of the engine and see any crusty, dried fluid it is probably coolant.

If you're not sure still, I'd also bleed/burp the system as it sounds like it is low (fill coolant through the radiator cap till full, top off overflow, and run engine till warm with the cap off and observe for bubbles. Then continue to monitor the levels when the engine is cooled off after driving.

GarethZA

Thanks for the reply and happy new year!

I've burped the system numerous times now, when I start up the car all I see is a tiny bubbles being sucked down then they come up again, seems to be with flow of water.

I'm going to try and clean up around the belt/pump area to then look for leaks, but would this not show up with a pressure test?

Interesting thing I found yesterday:

Lexus dealer told me thermostat spec is to open at 82degC.
I found that the thermostat did open fully, slowly when the pan of water was boiling but I wasn't convinced that it was operating properly as the temp rating is quote low at 83deg.
After probing the water, I found that the stat only started to open very slowly at 90degC, with a small gap appearing after a minute or so. IT was 100% open at boiling point.

Could this be a clue?

I'm concerned about the ingress or generation of Steam, I have now got a 50/50 coolant mixture in and still steam escaping after driving the car at operating temperature. I dropped all water from the radiator via the white butterfly screw on radiator then put in +- 3Lt coolant then topped off with water.

With regards to burping (cap off warming up, heater on etc), I lifted the front up a couple of inches last night, driving up on some bricks and didn't see any significant bubbles, squeezing radiator pipes etc.

What is strange is that the temp gauge seems to show rock solid temp in the middle of the dial, but steam is being generated somewhere...

Cheers,

Gareth.

ez12a

Nice find!

it looks like the thermostat is indeed bad. I'm looking at replacements and they're all rated for 82C.

Guess I'd start by replacing the thermostat. My guess is the steam could be caused by the low flow of coolant inside the engine causing the coolant to vaporize.