Just wanted to ask a question to confirm whether something is an issue or not...

I recently noticed that the temperature gauge in my 98 ls400 takes a while to warm up to the halfway mark. It seems to take a good 20-30 minutes (maybe a little less) before it reaches its optimal level (the half way mark). This slow rise usually occurs when I leave the car sitting for a while.

Now, Lately its been getting colder here in Denver, especially over night. This car wasn't doing this before (when it was warmer).

Does this mean my temperature gauge/thermostat is likely going bad, or does this mean the car really is that cold and needs to warm up?

 

My bet is the thermostat.

 

When was the last time the cooling system has been serviced? If one of those fail safe type thermostats is installed, it may have gone south so it is now in the open position.

30K intervals for the cooling system, coolant, thermostat and gasket. The coolant technically goes longer but the thermostat interval is suggested at 30K. Since enough needs to be drained off to just do this, replacing a partial amount of coolant is inefficient so the whole routine is just as easy.

 

you might want to go ahead and proactively replace the gauge sender, since it has lived 16 years in a bath of hot chemical water, as well as sixteen summers and winters in the hot and cold, then at least you would know that what you are seeing on the gauge is accurate info - I think that peace of mind is worth $15 and 15 minutes of work!

 

Well I took it to the lexus Dealer to have the oil changed, and the transmission fluid changed last Monday. I would imagine they checked the anything related to the coolant stuff stuff during during the change. In fact, now that I think about it, the gauge started acting funny maybe a couple of days after that oil/transmission change.

But I can't imagine what they did that would've caused it. In additionally, the weather has also gotten a lot cooler lately so I'm not sure what the issue is. However, I do know the car wasn't doing this at all the first week I had it (had the car for about two weeks now).

 

Does the heater temp correlate.

 

When you ask does it correlate, what do you mean exactly?

 

+1 on the gauge sender. Even if the thermostat was stuck open, 20 - 30 min to reach operating temp is ridiculous. Unless it is really cold outside. Smart to replace both temperature sensors since your right there.

 

I would judge after measuring the actual temperature of the LLC using a IR temp meter or a ELM327 scan tool 10 minutes after the engine is started.

 

I had a similar issue on my other Ls400 (a 94), except the gauge on that one wouldn't rise at all. It ended up contributing to bad gas mileage (I was probably getting about 12 miles a gallon). Cost me about $230 to fix.

This one seems to rise to the correct levels, its just slow getting there (10 minutes if I get on the highway immediately, 20 or so minutes if I'm just driving about town). So i assumed it was most likely a temp sensor going bad. But because these cars are so old and sensitive to cold weather, I wasn't sure if it was something related to the weather being cooler/colder, or the engine itself.

I'll definitely have a mechanic or the lexus dealer check it, I just wanted to know of there were some things I should look out for so that I'm not being told its something more expensive when it isn't.

 

I say its the temp gauge itself. I changed all that other stuff and nothing. Did the gauge and presto.

 

BTW my 92 goes from cold to half in about 5 mins.

 

Change the temp sender, gauge sensor, thermostat and flush the fluid. The problem will be fixed and you have done maintenance that is probably long over due!

 

When I first picked up my 95, the thermostat was jammed in the open position and the temp gauge wouldn't get any higher than 1/4. It made the car run like absolute garbage, because the engine would be stuck in warmup mode. a new $30 thermostat from the Toyota dealer fixed the issue and now it warms up very quickly.

The thermostat and coolant temp sensors are stupid easy to change on these, the biggest pain is just draining the coolant out of the engine for the t-stat.

 

I mean if your water is cold your heater will blow cold or not so warm air. If the heater is blowing hot air then it's probably your gauge or temp sensor, if it's blowing cold or not so hot air then it's probably you're thermostat.