Engine overheating, AC blowing cold air when set to max hot
Thread Starter
Driver School Candidate
Joined: Mar 2016
Posts: 14
Likes: 2
From: NJ
Engine overheating, AC blowing cold air when set to max hot
Tried turning on the heat in the car today and noticed that even at max HOT, the vents were still throwing in cold air. Soon after noticed the temp gauge going well past the 3/4th mark. Pulled over and allowed car to cool for 30 mins, but after 10 mins of driving the problem persisted. Checked coolant levels, and the reservoir is half full. There is some gunk in the overflow chamber though. What could this be due to?
Instructor
Joined: Dec 2015
Posts: 878
Likes: 232
From: Arizona
You have an air pocket in your cooling system. Could be caused by a leaking heater core or a leaking heater hose. These cars only run coolant through the heater core when heat is requested. The coolant must have leaked out of the heater core over the summer. If there was a leak anywhere else in the cooling system the level in the overflow tank will drop. Factory procedure to bleed the system is to make sure your radiator is full, put the cap on it, make sure the overflow is filled to the full mark, start the engine and set the climate control for max heat/temp, verify that the heater control valve is open (on the firewall on the passengers side top) and run the engine at 2500 rpms for 3 minutes. It should start blowing hot air within that time. Don't let the engine overheat and verify that your cooling fan is working. Recheck the coolant level in the overflow once the heat works again. If you do overheat the engine it can blow head gaskets and it's not a fun job replacing them (don't ask how I know!).
Lexus Champion
Joined: Mar 2011
Posts: 2,186
Likes: 728
From: Texas
Next time you're out for a drive, determine if the temperature rises when the car sits idle (in heavy traffic), and drops when the car is in motion (freeway driving). Other than low coolant level and bad electric fans as 911LE already mentioned, overheating can be caused by bad fan switch, thermostat not opening, clogged radiator, etc.
Thread Starter
Driver School Candidate
Joined: Mar 2016
Posts: 14
Likes: 2
From: NJ
You have an air pocket in your cooling system. Could be caused by a leaking heater core or a leaking heater hose. These cars only run coolant through the heater core when heat is requested. The coolant must have leaked out of the heater core over the summer. If there was a leak anywhere else in the cooling system the level in the overflow tank will drop. Factory procedure to bleed the system is to make sure your radiator is full, put the cap on it, make sure the overflow is filled to the full mark, start the engine and set the climate control for max heat/temp, verify that the heater control valve is open (on the firewall on the passengers side top) and run the engine at 2500 rpms for 3 minutes. It should start blowing hot air within that time. Don't let the engine overheat and verify that your cooling fan is working. Recheck the coolant level in the overflow once the heat works again. If you do overheat the engine it can blow head gaskets and it's not a fun job replacing them (don't ask how I know!).
Should I be doing a coolant flush?
Instructor
Joined: Dec 2015
Posts: 878
Likes: 232
From: Arizona
You don't need to do a coolant flush immediately but just keep in mind that you lost all of the long life properties of the pentosin coolant. You should be fine for the 2 year life of the coolant you added.
Pit Crew
Joined: Aug 2009
Posts: 235
Likes: 25
From: WA
Thanks for this, I think it was low coolant that was the problem, so I got some Prestone 50/50 pre-diluted mix to top it off, took almost 3/4 of a gallon bottle. The car isn't overheating now, and the heater works fine as well. Trouble is I put in the green Prestone, and I read that the LS takes only the red Pentosin. The Prestone said it can be mixed with any other coolant and has ethylene glycol as the base.
Should I be doing a coolant flush?
Should I be doing a coolant flush?
Lexus Test Driver
Joined: Sep 2016
Posts: 8,564
Likes: 389
From: PA
touchy subject for me, my coolant was low too, etc. Since filling, it has never moved down, except for the first day after refill (air?). I have even had the dealership drain/refill (am I to understand Lexus/Toyota does not flush?), and I further removed all the coolant from the reservoir and some from the radiator, to analyze the color. Then topped off with sllc2 both rad and reservoir, and again, has not moved in a few hundred miles (the other time did not move in 1,500 miles).
I can only add my experience, normally, yes, I would be super worried on a car if owned since new, since I check all fluids regularly. With an 11 y.o. car, I dunno. I have a sneaking suspicion that some escapes over time somehow, and the fact that the intake covers the reservoir, means many would never check it.
Refill cold, note the level, and drive 1,000 miles. If there's a leak imho the level should go down. If not, probably good. good luck.
I can only add my experience, normally, yes, I would be super worried on a car if owned since new, since I check all fluids regularly. With an 11 y.o. car, I dunno. I have a sneaking suspicion that some escapes over time somehow, and the fact that the intake covers the reservoir, means many would never check it.
Refill cold, note the level, and drive 1,000 miles. If there's a leak imho the level should go down. If not, probably good. good luck.
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Lexus Test Driver
Joined: Sep 2016
Posts: 8,564
Likes: 389
From: PA
You have an air pocket in your cooling system. Could be caused by a leaking heater core or a leaking heater hose. These cars only run coolant through the heater core when heat is requested. The coolant must have leaked out of the heater core over the summer. If there was a leak anywhere else in the cooling system the level in the overflow tank will drop. Factory procedure to bleed the system is to make sure your radiator is full, put the cap on it, make sure the overflow is filled to the full mark, start the engine and set the climate control for max heat/temp, verify that the heater control valve is open (on the firewall on the passengers side top) and run the engine at 2500 rpms for 3 minutes. It should start blowing hot air within that time. Don't let the engine overheat and verify that your cooling fan is working. Recheck the coolant level in the overflow once the heat works again. If you do overheat the engine it can blow head gaskets and it's not a fun job replacing them (don't ask how I know!).
When I replaced my Maxima's radiator, the heater did not work afterwards. What helped was to gently open the radiator cap when hot (towel covering, slowly)--hear a psssssssssssssssssssssssssssssssssssssssssssttttttttt! Closed it, without adding anything, heat began working, so I repeated. Then after cooled, I added to the reservoir....
Now, on this Maxima job, I mixed the green which was brand new, with Dex Cool, which I had handy. That was over 1 1/2 yrs. ago and no issues. I have subsequently seen the debate on mixing Dex Cool and would not do it, but can only report my experience, that it had no effect/gel'ing....
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Pole Position
Joined: May 2011
Posts: 227
Likes: 2
From: CA
Several posters have commented on only using the Toyota pink coolant or the Zerex knockoff. The comments ran around the possible corrosion which would be subtle and take some time. All the manufacturers of coolant say they work with everything. Maybe they do but this is cheap insurance. If it was me, I'd drain and replace with the right stuff.
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