King0824

So I just bought a 99 Lexus ls400 and the coolant temperature gauge would read above halfway point each time after a few minutes of driving but the car wasent overheating . So I replaced the coolant temperature sensor and the thermostat at the same time and while I did that I drained all the coolant in the engine block and the radiator because the previous owner was using green coolant. So after I did that I filled the front of the engine filler off with coolant up until it didn’t take anymore and topped off the coolant reservoir. I turned the car on and I heard ticking noises coming from the left and right side of the engine, I did change my spark plugs too but idk if it could be that or I also heard it could but from engine overheating. It used to tick a little just on the right side but now both sides and a little more louder. Then while bleeding the coolant after letting it idle for 10 minutes I proceded to push the gas to 2000 rpm like the instruction states and after a minute my engine started making a weird kinda loud rattle noise so I turned it off. After letting sit for an couple minutes in the meantime while I changed my clothes and got ready cause I had to go somewhere and it’s my only car after 5 minutes of driving the rpm went all the way down and the car had no power anymore to move and the steering wheel got really hard. I turned it off and waited for a couple minutes. No leaks at all. Reservoir was still at full. The hoses were pretty hot. The top of the engine wasent really hot to the touch but the thermostat housing was really hot to the touch. So I turned the car on again and left the reservoir cap open hoping maybe some air would bleed out and after a couple minutes of idling I took it for a spin and it didn’t shut off after 20 minutes of driving straight. But the the rpm’s idling at 0 now and it looks like the temperature gauge still doesn’t work. How can I fix the rpm gauge idling at 0 (looks like it’s not accurate because car doesn’t shut off) and temperature gauge not working? Also I have the BlueDriver obd2 and when I try to read live coolant temperature so I can see the temperature while driving it says “not supported”. I don’t know what the issue with my car is? And what can I use to see my live coolant temperature if my temperature gauge isn’t working?


Edit: I turned my car on today and idk if the gauges work now or aren’t accurate but the temperature gauge started at the bottom and slowly went up and the rpms started at 1000 and slowly went down after 8 minutes of idling.

400fanboy

This is the normal temp gauge & idle RPM indicator. Both are abnormal in your picture. However, since you never mention the engine is running rough, I suspect this is instrumentation failure rather than your engine actually running at 350rpm. This may be causing the coolant temp gauge to also be reading incorrectly. Key word: may.

Attachment 485260

As for OBD2, it should be able to pull coolant temp and other associated stats from the engine. Are there any other sensors or values which fail to provide live readings?

Attachment 485261

OBD failure, gauge cluster failure, engine running weird then running fine. All are intermittent. Sadly this suggests, but doesn't confirm, ECU failure. Be mindful however, 98+ models this is less common. But not impossible, it just takes longer.

Hard to determine whether "weird noise" and "hot hose" are actually weird, or just new to you.

Suggest digging through OBD to find accurate values for engine RPM, temperature, etc to confirm instrumentation failure. Also make sure you're pulling the correct coolant temp value from your OBD reader. Or try another one.

https://www.clublexus.com/forums/ls-...capacitor.html

King0824

So my rpm’s was working fine before until after I thought bleed the car out of all the air. So when I took it to a drive, after 5 minutes it literally stopped moving and the rpm went all the way down and I couldn’t move the steering wheel, I think it went into “limp mode” if that’s what it’s called and then I turned it off. After I turned it back on again my rpm’s would idle at 0. Now the car doesn’t overheat . The live scanner tool works now and I could read the live data. So the rpm’s are about like 300-400 off. And the coolant temperature is about 180- 185° F but the temperature gauge needle is all the way up close to the hot. Also by the way I should mention that sometimes it slips gears which I heard could also be from a bad ECU

400fanboy

Wait, I don't understand. The RPM went down? Did the car stall & you couldn't move the wheel because the engine stalled?

Were the RPM's 300-400 off of what was indicated? Or it was idling at 300-400?

Was the car actually overheating, or was the car "overheating" because the gauge was reading high? I would trust the thermostat and coolant temp sensor through the OBD over what the gauge shows.

The live scanner tool didn't work before, but now it does?

Are there any stored codes? Or any CEL at all?

Transmission also sometimes slips?

This keeps coming back to ECU, ECU, ECU. You have like half of the symptoms on the megathread.

https://www.clublexus.com/forums/ls-...l#post11490223

Replacing your ECU is not simple. You cannot just match P# because the immobilizer. Repair is the best option, not replacement.

LeX2K

If coolant level is low engine temperature reported will not be reliable. Put another way you can cook the engine even if reported temperature is normal. Going by your description the cooling system could be filled with rust and clogged.

King0824

Yes, Yes it stalled. So the RPMs are 300-400 off of what the OBD scanner is indicating yes. Also what I forgot to mention is the first time I installed the thermostat and I turned the car on after about 10 minutes of idling it started leaking from the thermostat housing and I turned the car off. The engine was smoking a bit and I noticed a little opening on the bottom of the housing where you bolt it in. I’m guessing because I didn’t bolt in the bolts evenly, I did them one by one. So maybe that could have messed up the ECU somehow? Because it overheated.

King0824

I took it for a spin today. This is after about 5 minutes of driving and I parked the car and took both of these pics from my obd scanner tool and gauge. Also when the speed gauge reads at 40mph the obd scanner reads at 35mph but anything at lower speeds than that it is accurate.





There is no current codes on the car and this code I’m guessing was from before.

400fanboy

So fwiw, two sensors reading engine coolant. One for the gauge, one for the computer. You replaced the one for the computer. I'd be more inclined to trust the new part.

There is a easy test you can perform on teh gauge. Ground out the single wire connector (temp sensor) on the thermostat housing area with the car on. The gauge in cluster should go to full Hot. If it does not, the cluster is the problem. If it does, the sensor and or connector or wiring in the connector is bad.

Lex also brings up good point, green coolant could be mixed and ****ed up the internals. What did the thermostat look like when you pulled it? Was there corrosion? What about pulling the cap to the radiator and shining a light in there. Or the coolant you drained out.

King0824

when I pulled out the old one there was a little corrosion but only around the o ring. Cause I tried to take it out by hand and it didn’t want to come out. So I took a flat head and just softly prided it and it came off easily with that. But no corossion on the actual thermostat. Yesterday I cleaned out the radiator by plugging my water hose through the top of the radiator and at first it came out a little red from the new coolant I put in ( I drained the radiator already) but I’m pretty sure it cleaned out everything cause the water came out clear at the end. After about 30 minutes of driving today and monitoring the rpm’s, speed, and temperature on my obd scanner and the guage( The guage wasent accurate at all) the car doesn’t overheat at all, the temp stay between 180° - 185°. I’m not worrying about the car overheating anymore and no coolant is leaking or nothing. So only the gauges don’t work and the car sometimes slips gears. So i think you’re right it is most likely the ECU. Do you know the best website and or place were i can get it repaired?

King0824

well the coolant level today was at full the whole time and it doesn’t leak and I cleaned out the radiator yesterday with a hose. So I don’t think there’s any clogs. Idk

King0824

actually tomorrow ima try what you told me. By ground out you mean is unbolt the temp sensor but still have it connected touch the thermostat housing right? If it just the sensor then worst scenario the reason my rpm and speed not working and the car stalling on me and the car slipping could be from a bad tranny and I would have to replace that.

400fanboy

Everything about the ECU is in this thread

https://www.clublexus.com/forums/ls-...capacitor.html

I would continue testing your gauges, they can fail on their own. You are able to pull the ECU reasonably easy and visually inspect it as well. Be very very careful, it's a highly sensitive piece of old electronics.

It's not just those issues you listed. You also had OBD connection issues. You had idle\stalling issues. Variably inaccurate speedo.

I would drive the car some more & get a feeling for it's behavior before condemning the ECU. And I'm just one person on the forum, I may be wrong as well.