NeverSatisfied

My old RX330 (now owned by my folks, has about 51K mi.) While parked on a slight incline with the engine running and A/C on, the coolant temperature needle went all the way up to the 5th line on the gauge. The A/C went warm. After driving off, the coolant temperature went back to normal and the A/C was cool again. Can anyone explain this?

The G Man

Time to replace the the thermostat

salimshah

Thermostat is one possibility and the other is the cooling fan (its switch) as well.

Also simple thing as a clean radiator does wonders to the cooling system.

Q: Does the coolant retain its properties one you reach extreme temperature? Should the coolant be replaced once you see it steam off?

Salim

The G Man

Actually if he start driving off and temp went back to normal, it more likely the its the cooling fan than the thermostat.

NeverSatisfied

I'm not too sure what you're asking, but there was no steam whatsoever coming out of the hood when the gauge needle was almost at "hot".

I'm just surprised that this is happening, when I thought I cared immaculately for this car (service EVERY 5K miles and all the major services at 15K, 30K & 45K. Or is this normal wear & tear? *secret: this is why I don't keep cars for too long*

Lexmex

What's the color of the coolant that you see in the reservoir (left side of the engine bay, biggest reservoir you see)?

Claude7629

I agree with THE G MAN. Let the car idle until the temp rises and see if the fan comes on. The car can cool down when moving due to increased air flow. The fan should come on when engine temp is not maintained by movement of the vehicle.

IS3666

Check your coolant level... If it is low, your radiator is leaking.

The G Man

They cannot check everything on those schedule services. Even if they did, the parts can still fail in between the services. No its not normal wear and tear, you should get the dealer to check it out. Have them check out the entire cooling system. BTW, I use the same excuse for trading in my car every 2 or 3 years

NeverSatisfied

Thanks everyone for all your input! Lexmex: I'll get back to you on the color.

Lil4X

It still sounds like the fan is not switching on at high temperatures. That would account for the sudden rise in temperature that subsides when you drive off. Yes, the AC would also be affected as its efficiency also depends on air flow over the condenser coils when motionless in traffic. Either the fan has failed, or more likely the thermostat that controls its operation has gone bad.

salimshah

Lil4x's message needs a bit of clarification ..

There are two thermostats ..
Thermostat-valve ... This is in the coolant path, which does not allow flow from the radiator till the engine reaches operating condition [If this was not there (or stays open) you would need a long time to get to operating temp. If it remains shut you would over-heat while the radiator would be cold]

Thermostat (cooling fan switch)
This is an electrical switch that sits in the water-jacket of the engine block, and it switches the cooling fan (on the radiator) on or off when the coolant temperature reaches a certain temp above the optimum temperature.


Salim

NeverSatisfied

Just an update: The temperature would shoot to hot when driving in normal conditions/flat roads. They took the RX to the dealership today. The radiator needs to be replaced. Around $1K with labor. Is this normal for 68K miles??

ggebhardt

Have you owned the vehicle from new? If not, the coolant system might have been neglected prior to your purchase and clogged arteries in the radiator caused it to need to be replaced.

If you owned it from new and did the proper maint, then there is no way it should have gone bad at 68k miles.

tfischer

That just happened to me a few weeks ago.
My '04 started to overheat while driving. The dealer checked it and found that the radiator was leaking and needed to be replaced. Although I still have a few months left on my CPO warranty, which would have covered it ($750 or so), the service tech mentioned that my '04 fell within a range of VIN numbers that had bad radiators, and that Lexus "extended" the original factory warranty on those cars and would replace them. (So I was double covered.)
I searched here and did find some posts about the radiator problems from posts in '05 and '06, since that's when the original warranties ran out on the new '04 cars.
Before you pay for the replacement, have the service folks look this info up and see if your car is in the covered group.
Good luck.