pa2phoenix

So my o7 es350 with 75k on it just started acting really strange. I noticed while at a traffic light the temperature gauge was right in the beginning of the red zone. After being there for around 20 seconds it dropped back into the normal range. Then while driving it would randomly shoot up very quickly and then back down again, just as quickly (a couple seconds)

I sat and idled it for a while and the gauge slowly creeped back into the red, then in a matter of 15 seconds dropped back into the normal range. I checked the fan, and coolant levels and both seem to be fine. I called the dealership, but they were no help at all. Has anyone seen this on this car before?

Note: it's hot here in PA right now, around 90 degrees.

Lexi66

When was the last time/mileage that you changed your anti-freeze?

pa2phoenix

Probably been about 40k miles if I had to guess. Could that really be the cause?

Bill Dowd

there are two possible problems one being the fan sensing switch coming up slowly or the radiator could be clogged have a good radiator shop check the radiator for clogging of garbage junk etc. or see if the fan switch is coming on. Another test is to leave the air conditioner on during a hot day if the gauge stays normal the gauge doesn't move up then I suspect the fan switch is going bad or you radiator tubes are full of calcium from old antifreeze. Again have a good radiator shop check the radiator tubes they should be clear. Another trick I do to help my air run cool is once a year go to the self cars wash and spray the air condenser with hot soapy water do not get the engine wet.

jcat_350

I'm thinking coolant temp sensor. Definitely replace the coolant and have it glycol tested to be safe.

pa2phoenix

So after I let the engine cool completely I checked the coolant level, and it was just a little low. It probably took about a cup of coolant total. I drove it today a few times, and the engine temperature was very stable. I'm going to get the coolant system flushed this week to be safe. I'm a little concerned that the coolant was low because it's definitely not leaking. When I change the oil I'll keep a close eye on the color to make sure the coolant isn't bleeding into the engine. Thanks for your input guys.

kewl

Thermostat...

mspearl95

i was thinking that it may be air bubbles in the system.

jcat_350

air in the system would indicate a leak somewhere.

OP, worst case slide a sizeable piece of cardboard under the car overnight to catch any leaks. I would not wait to check the oil for coolant, that should be done ASAP.

MadMax96

+100

A car of mine in the past did the same thing. The thermostat is like a valve that opens and closes to allow the coolant to flow between engine and radiator.

When the engine is cold, it's closed so the engine will warm up faster. As the temp goes up, it will open to allow the coolant to flow to keep it regulated to the proper temp range. Kinda the same way your A/C in your house goes on and off to keep a set temperature.

When they get old, they'll often get stuck closed - causing an overheat condition. Then when they finally pop open, the coolant flows and your engine cools right off.

Newer thermostats are made differently now so when they get stuck, they are stuck OPEN - this avoids your engine from overheating, but it will take longer to warm up (more noticeable in winter when you can't get much heat from the vents).

Good thing is that a thermostat is like a $5 part. Bad thing is it'll cost much more than that to have it replaced... and if you do it yourself, it's just a frickin mess because coolant will generally get all over the place.

So unless your car is throwing a code to show a bad sensor or something, I'd place my bet on the thermostat being the cause.

Good luck........

MadMark

I second the thermostat motion. I doubt your radiator is clogged, a cup of fluid shouldn't make that much of a difference. Don't drive it if it's getting anywhere near close to the red. It would be a shame for you to end up with a blown head gasket and have to have the head milled and a new gasket put on. (can you tell I've had this happen before? FYI it was a 1982 Toyota Supra.) You won't make a mess of your coolant if you simply drain it at the radiator. Put a spill pan underneath because the block and heads will have some coolant in them too (depending upon the location of the thermostat.)

pa2phoenix

Update:

Car has been driven maybe 4-500 miles since then with zero issues, and with the temperature gauge not moving an inch, even under various driving and heat conditions.

Going to keep a close an eye on it, and i'll probably change the thermostat in a couple months when I need to tires/brakes/rotors as well. Thanks for the input guys.

jkayca

If you are still concerned about the loss of fluid, check around the water pump for signs of leakage. Mine leaks albeit very slowly. Mechanic said it isn't an uncommon occurrence on the ES.

3foreign

replace reservoir/radiator cap and purge coolant system. Should solve your problem.