I have 2004 GS 300 155K miles. Car overheated this week and lost all the coolant.

Towed to a repair shop and they replaced water pump, thermostat, timing belt and radiator cap. (Last year the radiator was replaced). Also, I had an oil change 60 days ago and they found that I have lost at least 2 quarts of oil, however found no issues with oil and coolant mixing anywhere.

The strange thing is when the car is parked and idling, (over 30 minutes) no overheating issues. Since we live in AZ, it has been over 100 degrees this week. However when they conduct a test drive, the radiator pressure goes to >22 psi and the car overheats. They swapped out the thermostat to make sure that it was working properly.

They conducted a pressure test on engine block and found no leaks.

Any advice on where to look next?

 

Idling in hot weather is alot different than driving, once a load is on the engine the heat increases drastically. It may idle all day long in 100+ weather and still not overheat, but drive a block or two and it may top out the gauge instantly.

Are the radiator hoses hard when you squeeze them after a drive?

Otherwise you will need to know the actual results of three tests, compression, leakdown, and radiator pressure. Simply 'pass' or 'ok' doesn't cut it when coming from a random shop. Those three tests done correctly will tell you what the problem is.

2 quarts is a good amount of oil, your not smoking out the back at all?

 

head gasket or cracked head... that's the only way you get that kind of pressure that quickly... so long as you aren't being hard on the car, coolant temp should lower once you start moving if it was a simple heat exchange issue - air flow over the radiator even at 25 mph is more than you get from the cooling fans...

there is one very easy way to determine for sure if you have a head gasket / cracked head issue - open the radiator cap and run the engine... if you have a steady stream of bubbles coming out, then 90% sure you have a head gasket / cracked head issue... to be that 10% more sure, you pay a shop, or rent the tester from somewhere like autozone - just like this: http://www.autozone.com/autozone/acc...ester/_/N-25dh

basically, you put the fluid in the cylinder, use the bulb to suck air out of a radiator / coolant space - if the fluid changes color it means there are hydrocarbons present, which means exhaust in the coolant, which would confirm head gasket / cracked head...

 

It's a great possibility that there is air in the coolant system. Bleed it over and over. Drive it a few miles and bleed it again.

My IS300 had an air pocket after I installed a new radiator. I bled it for 45 minutes at idle. The air pocket was before the heater core, so I was able to tell that it was blocked due to not having heat. I drove the car up the road and back, and I could hear the water rushing through--forcing the air pocket along. I took the car back home and bled the rest of the air out. That was about 4 months ago, and I haven't touched the coolant system since. No problems at all.

Good luck.

 

check the radiator hoes like how 99 gs3 said.
maybe you have a cracked radiator and you dont even know about

 

if the radiator was cracked, it wouldn't build excessive pressure, it wouldn't build any pressure...

 

you can als check the fans make sure they are coming on properly check the temp sensor for the fan.

 

Please check these, but I highly doubt that is the issue, as it does not overheat at idle, and the fans become worthless around 25 MPH, as there is more airflow from the movement of the car than there is from the fans... if the fans weren't working, I would expect the car to overheat relatively quickly sitting still...