HELP - 1994 Lexus LS400 running cold.

[HTSS_TR]

My 1994 Lexus LS400 had a small heater hose leak few weeks ago, got over-heated and lost most coolant when it got home after 12-15 highway miles. I flush out the remaining coolant and added new coolant and water for 50-50 mix.

After that the engine ran very cold, the coolant temperature is now less than 1/4 mark while it should be 1/2 mark, and it take forever to get to that 1/4 mark even after driving 70+ mph on highway for 10-15 miles.

I bought an OEM temperature (180 F) thermostat at Autozone and after replaced the coolant temperature gauge shows the same level, 1/4 mark, as before changed. Because the engine is running cold at all times, my gas mileage suffered about 30-40%, it was about 19-20 MPG last month before coolant got over-heated, now it is about 12-13 MPG. My main concern right now is this car is needed to have smog check in 2-3 weeks for renew registration, it will not pass smog check with current cold engine temperature.

Other than the thermostat to control the coolant temperature, what else can be failed such that the engine coolant temperature is so low ?

 

[Falcon_LS]

Had a similar problem with a 5S-FE in a Camry, and the problem went away after replacing the ECT sensor. Have you ever replaced it on yours before?

 

[crazyoildude]

Did you try a 195 degree?

 

[HTSS_TR]

Originally Posted By: Falcon_LS
Had a similar problem with a 5S-FE in a Camry, and the problem went away after replacing the ECT sensor. Have you ever replaced it on yours before?


Is ECT stands for Engine Coolant Temperature ? If it is, the ECT sensor in my is OEM and never been replaced.

 

[HTSS_TR]

Originally Posted By: crazyoildude
Did you try a 195 degree?


No, I didn't try it. With OEM 180 degree thermostat, the coolant temp, my guess, is no more than 120-130 degree after 15-20 miles highway drives, the top of the engine is barely warm to the touch, before it was hot. So the problem is not with either thermostat, old or new.

 

[mechtech2]

Could be an air pocket.
Keep your reservoir 1/2 full and give the car a few hot cold cycles.

 

[robshelton]

I agree. Check this link:
http://www.justanswer.com/questions/20okm-overheating-lexus-sc400

The OEM thermostat probably had a "Juggle Pin" to let air out of the system. Does the stat one have one? I've drilled holes in a few to help them bleed the air out of the system. Still could be the ECT sensor but I'm betting on a air pocket.

 

[Falcon_LS]

Originally Posted By: HTSS_TR
Is ECT stands for Engine Coolant Temperature ? If it is, the ECT sensor in my is OEM and never been replaced.


Yes it is, sorry should have made that clearer. Might want to try 'burping' the system first, as others have suggested though. Hadn't thought of that one.

 

[HTSS_TR]

I checked and found there is no air pocket in the coolant system. The reservoir/expansion-tank was 2/3 full at cold start and is exactly the same level after 15 miles drive in the low 80's heat. The coolant temperature gauge is barely above the cold mark after the drive, it was way above that cold mark few days ago.

I think the culprit is the ECT sensor, Autozone has an after-market one for about $14. I will try to replace the ECT sensor and hope that will fix the cold engine temp problem.

 

[1999nick]

I do not know what kind of a thermostat a Lexus uses, but if it is anything like the kind used in most cars, if it is opening correctly, at 180 degrees, the water will be 180 degrees, at least. I would check the thermostat to see if it is opening at the correct temperature by doing the time-tested putting in a pot of hot water and an appropriate thermometer and observing just when it opens. Also, make sure it is not installed upside down.

If the Lexus thermometer is some kind of a fancy computer controlled electronic gizmo, ignore this post.

 

[HTSS_TR]

Bought Engine Coolant Temperature (ECT) sensor from Kragen, but the mechanic said the problem was not that sensor, the water temperature sensor that send signal to the coolant gauge failed (after quick diagnostic). He ordered the sensor and replaced the OEM unit, the total cost of sensor and labor is only $40, all is good now.

 

[mechtech2]

YOu may have 2 coolant sensors.
One for the gauge, and one for the computer.

 

[1999nick]

Originally Posted By: HTSS_TR
Bought Engine Coolant Temperature (ECT) sensor from Kragen, but the mechanic said the problem was not that sensor, the water temperature sensor that send signal to the coolant gauge failed (after quick diagnostic). He ordered the sensor and replaced the OEM unit, the total cost of sensor and labor is only $40, all is good now.


Good to hear that this was a fairly simple fix. One thing, tho: Has your fuel economy returned to the previous level?