Jlacck

I tried searching the forums and I cam across some posts that offered a little insight. However I think my situation might be a little more unique.

I have a 1998 LS400. Lately its been incredibly hot here in the Atlanta area with temps approaching 100 degrees. I'm noticing my car temperature gauge starting to rise after I've driven the car for about 30 minutes. (see picture)



This seems to only happen when it is 95 degrees or higher outside and when the AC is running. The needle drops quickly when I turn off the AC and run the heater. (The temp doesn't rise I drive he car at night or when its lower than 95 degrees during the day).

Two weeks ago I took it to my mechanic who thought it needed a new engine thermostat. The only change I've noticed is that the temp needle doesn't rise as high as it did before the change.

I showed him the pictures from my phone. He told me when its really hot like it has been lately, its not unusual for the needle to rise or fluctuate a bit. He says if/when it starts to approach the line that's close to the red that's when its a real problem. He also said he didn't see anything wrong with my fan/radiator or the engine filter.

So I'm a little stumped here. Has anyone else had an issue similar to this? If so, what fixes did you use to correct the problem?

Stroock639

the needle should never go above halfway. under normal conditions it should be right above the 2nd tick mark. the coolant isn't low or really old is it?

dicer

Things to do and to check, temp sender for the gauge, flushing scale out of the cooling system, make sure between the condenser and radiator has no debris between them and both are clean for air to pass through.
Scale can build up in the tubes of the radiator and usually they need to come out to be cleaned good. And with these plastic tank radiators likely they just need to be replaced. Are you sure the transmission is working correctly? It does have an oil cooler in the lower radiator tank and can heat up the engine coolant.
You need a good honest measurement of the temp of the engine and what the sensor is showing it as. A real time scan tool will show that. Does it heat up when driving at 50 plus MPH in the heat?

Losiracer2

make sure the electric cooling fan is turning on when the A/C is switched on. If its not, the condenser will heat up the radiator a lot more and cause a temperature fluctuation.

This also happens if you didn't bleed the cooling system properly or if air has somehow gotten into the system.

jaaa

Also, check your crank pulley for a separating middle section. If it slips enough, you could be loosing cooling action on the fan.

Stereorob

tempature / overheating is one of the only things that really scare me about these cars cause of aluminum block. that's one way you can actually kill an Ls400. I got an OBDII scanner so I can monitor my tempature cause I don't trust my gauge

djamps

Mine doesn't move at all. Even in 100+ degrees. Something is wrong with your cooling system. Some good comments so far, I don't have much to add... could be alot of different things. Radiator clogged, water pump going bad, air in system, low coolant, slipping belts, fan clutch, ect ect...I'd start with the fan clutch and make sure it's 'kicking up' the speed when you're seeing those temps. It's pretty obvious, the engine sorta sounds like a big truck when the fan kicks up. I've heard mine kick in a few times in really hot weather. if I were you I'd roll the windows down and kill the A/C until you figure it out. The added thermal stress on the engine could start causing damage to your head gasket and other stuff.

lextout

if the radiator is old, i would just change it for a new denso, there around 90$ online.

KJG92

You can check all the stuff mentioned but if the radiator is stock then I'd pull the thing out and have it cleaned or just replace it. Does it cool off when you drive or does it matter. If it rises when you are driving and when the a/c comes on then either the second fan is not working or the radiator has some build up in it. The needle in our '92 goes to a little under half and stays there. Always has no matter what temp it is outside. We did change out the coolant temp sensor though doing some general maintenance.

Jlacck

My apologies for the delay in getting back to everyone... Its gotten pretty hectic at work. I wanted to thank everyone who did take the time to comment and offer some thoughts or feedback. I'll try to answer everyone's question on this post:

@Stroock639:

Quote:

the needle should never go above halfway. under normal conditions it should be right above the 2nd tick mark. the coolant isn't low or really old is it?

the coolant is somewhat fresh I should say. Of course I probably may need to do an actual flush/change, but I just poured some new coolant in the engine about a month or so ago. It was low at that time.

@Dicer:

Quote:

Things to do and to check, temp sender for the gauge, flushing scale out of the cooling system, make sure between the condenser and radiator has no debris between them and both are clean for air to pass through. Scale can build up in the tubes of the radiator and usually they need to come out to be cleaned good. And with these plastic tank radiators likely they just need to be replaced. Are you sure the transmission is working correctly? It does have an oil cooler in the lower radiator tank and can heat up the engine coolant.
You need a good honest measurement of the temp of the engine and what the sensor is showing it as. A real time scan tool will show that. Does it heat up when driving at 50 plus MPH in the heat?

The heating seems to only occur when its REALLY hot outside. What I've picked up on is the car has to be running for at least 30 minutes and the temp has to be over 95 (according to the outside temp reading in the Lexus). When its this hot it, the engine temp will start to rise even if I'm driving regular city speeds. However, the car does not seem to "overheat" if it is lower than 95 degrees outside, no matter how long or fast I'm driving.

@Losiracer2:

Quote:

make sure the electric cooling fan is turning on when the A/C is switched on. If its not, the condenser will heat up the radiator a lot more and cause a temperature fluctuation. This also happens if you didn't bleed the cooling system properly or if air has somehow gotten into the system.

Bleeding is where you run the heater on high and keep the rpms between 2000-3000 for 15 minutes right (I read this somewhere)? If so, yeah I actually tried that a couple of weeks ago. But I'll run this by my mechanic to check into as well.

@jaa:

Quote:

Also, check your crank pulley for a separating middle section. If it slips enough, you could be loosing cooling action on the fan

I'm wondering if my mechanic inspected for this... So you are saying if the fan isn't kicking in, is possibly a bad crank pulley?

@djamps:

Quote:

Mine doesn't move at all. Even in 100+ degrees. Something is wrong with your cooling system. Some good comments so far, I don't have much to add... could be alot of different things. Radiator clogged, water pump going bad, air in system, low coolant, slipping belts, fan clutch, ect ect...I'd start with the fan clutch and make sure it's 'kicking up' the speed when you're seeing those temps. It's pretty obvious, the engine sorta sounds like a big truck when the fan kicks up. I've heard mine kick in a few times in really hot weather. if I were you I'd roll the windows down and kill the A/C until you figure it out. The added thermal stress on the engine could start causing damage to your head gasket and other stuff.​

I suppose I can try keeping the windows down. In stop and go traffic, this heat becomes unbearable. But I agree that its something I definitely need to get resolved ASAP before I do any major damage to my engine.

@Lexout:

Quote:

if the radiator is old, i would just change it for a new denso, there around 90$ online.

I'm pretty sure I'm still riding on the stock radiator. My initial thought was maybe I need to replace the fan or something is going bad with my AC

@KJG92:

Quote:

You can check all the stuff mentioned but if the radiator is stock then I'd pull the thing out and have it cleaned or just replace it. Does it cool off when you drive or does it matter. If it rises when you are driving and when the a/c comes on then either the second fan is not working or the radiator has some build up in it. The needle in our '92 goes to a little under half and stays there. Always has no matter what temp it is outside. We did change out the coolant temp sensor though doing some general maintenance.​

Sometimes it will rise and stay there for a bit, and then it goes back down. But here is the kicker.... yesterday I was driving home from work (this is primarily when the car over heats), the needle started to rise (heat index of 100 outside). As usual I had the AC on and was in stop and go traffic on the highway. As soon as it started raining and , the temp needle started to drop. (and yes the AC was still running).

So whatever this is, it has something to do with the high heat index effecting my engine somewhere. Any other thoughts that you guys can add for me to run by my mechanic is always welcomed.

KJG92

I'd say it is a flow issue and maybe time for a new radiator or remove it and have it hot tanked and rodded out. Sometimes that is more than just replacing it but I have not priced a radiator for one of these. There is a normal range for a reason but it is a warning sign. Here in ATL it has been stupid humid and the high temps don't help that.