Overheating

AAL readers, I have a 1992 400LS well maintained with 120K miles on it. Recently I drove to Las Vegas from Los Angeles with the ambient temperature around 110 deg F (120 deg F in Baker) most of the way. Normally the coolant temperature as shown by the guage on the dash is just slightly above the second graduation mark. In the past I have made this trip and the temperature has remained normal or very slightly above normal even when stalled, in heavy traffic with the air conditioning on, for more than 45 minutes. On this most recent trip however I noticed the following. With the car moving at highway speed (40 to 80mph and airconditioning on), the coolant temperature was very slightly above normal. When moving at below 40mph, ac on, the temperature started to increase. When stopped or stop-and-go with ac on, the tempeature started to increase rapidly. I never let it get near the red line. If I turned-off the air conditioning the temperature returned to normal i.e. to the second graduation mark. Returning to highway speed I was able to turn-on the air conditioning again and everything was normal. Inspection of the engine revealed a full coolant reservoir and no apparent leakage. The auxilliary fans moved freely. Since I returned to the Los Angeles area everything has been normal (ambient temperatures around 100 deg F), even when temporarily hung up in traffic. I would appreciate any of your thoughts on what may be the cause of this situation before I take the care to my Lexus mechanic. Your thoughts and suggestions are appreciated in advance.

Reply to
elmarsadice
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"The auxilliary fans moved freely" - but are they running flat out when the temp is getting too high?

Reply to
ib

This sounds like a problem I had about a month ago with my '93 ES300. The engine would be fine when idling, but when driving any significant distance (20 miles or so), the engine would gradually heat up. The problem turned out to be a non-functioning radiator, even though the fluid levels were fine. My temp gauge normally hangs right around the middle.

Reply to
McPhallus

My problem is a little different. It operates correctly at speed on an incline even with the ac on. It heats up with the ac on when in stop or stop-and-go traffic. It also operates correctly when in stop-and-to traffic with the ac off.

Reply to
elmarsadice

They moved freely with the engine off i.e., the rotors were not locked up. I don't know if they were running in the hot condition as I didn't want to stop on the freeway to check.

Reply to
elmarsadice

elmarsadice quipped:

When you're moving, there's air cooling the front of the radiator, when you're not, the fans alone keep the coolant from overheating. If the temp is climbing when you're not moving, it means the coolant isn't being cooled sufficiently enough to keep the engine at normal level.

Consequently, there's only a few things it could be:

  1. Your thermostat isn't functioning properly.
  2. The fans are not working properly.
  3. Your coolant level is low.
  4. Your radiator is clogged.
  5. Your coolant needs replacement.
  6. Your water pump is failing.
  7. You have an air pocket in your radiator that's preventing proper coolant flow.

If your thermostat isn't working properly, it's not opening up enough to allow enough coolant past the radiator to keep the engine cool. I don't *think* that's the problem here since the problem would be inherent at any speed.

If the fans aren't working properly, they aren't turning on when you're in stop in go traffic. This is a likely problem.

When was the last time you had a radiator flush and fresh coolant put in? Coolant has a life span just like oil.

A clogged radiator will also cause overheating. A flush will usually rid the radiator of any clogs.

If you haven't checked recently, check your coolant level.

There's no real way to check your water pump except if there's noticeable loss of coolant, leaks around the pump, bearing squeal or of course, sudden engine overheating.

If you've had your radiator recently flushed and it wasn't filled correctly (e.g. let it idle for at least 10 minutes with the cap off), you could have an air pocket in the radiator.

I'm sure there's other folks in this newsgroup that can offer other suggestions but one of the 7 items I listed above has always been the root cause of any sudden, unexplained engine overheating for cars I've owned in the past.

Reply to
amstaffs

The symptoms described by the OP are classic symptoms of a poorly or non-functioning cooling fan. Check their operation first.

Reply to
Ray O

If you have a removable radiator cap then starting with a cold engine, remove the cap, start the car and watch the coolant. It should pretty much sit there showing only a little engine vibration. Depending upon outside air temp to a small extent, within 10-15 minutes you should see the coolant start moving and increase intensity for a bit as your stat opens fully. If you see lots of flow right away, your stat's probably stuck open. This shouldn't cause you to over-heat tho. If it doesn't start moving the stat's stuck shut or your water pump isn't doing it's job. While the hood's up and the engine's warming you can watch your fans for proper operation too. (Just don't stick your fingers in them.)

Reply to
Dave's

Reply to
elmarsadice

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