Coolant temp sensor bad, but how? (1 Viewer)

[tiomateo]

I have 99 LC100, I posted a separate thread about the steering rack the other day.
But then a new problem happened.
The shop did not have time to do the steering rack stuff so my plan was to take it elsewhere, but they DID change both radiator hoses. I know they were OEM parts because I picked them up myself from Toyota.

Anyway, that night after changing the hoses, having only really driven a few miles home, and then down the street for dinner, when I came home a check engine light came on and I could smell coolant burning.

The next morning I take it back to the shop, they take a look and find a bad coolant temp sensor. Then the car sits for 5 min while I chat w the guy, and then when I try to start it, it’s a hard crank no start.

They are telling me it’s totally random and by chance that this new sensor issue arose.

Just frustrated because every time I went to that shop, it seemed my truck left worse off. I don’t want to throw them under the bus as it’s a highly respectable shop… but damn.

Curious what the community thinks typically leads to or causes this sensor to get fried suddenly.

TLDR: what causes a coolant temp sensor to go bad?

Thanks everyone

 

[Malleus]

age

 

[Rhetoric]

When hoses in the cooling system are changed, coolant needs to be refilled and burped. Was this done?

Perhaps a steam pocket formed by the sensor due to not burping the system and wrecked the sensor?

I am merely hypothesizing. But I know these trucks need to have air purged from the cooling system when changing components...

 

[tiomateo]

When hoses in the cooling system are changed, coolant needs to be refilled and burped. Was this done?

Perhaps a steam pocket formed by the sensor due to not burping the system and wrecked the sensor?

I am merely hypothesizing. But I know these trucks need to have air purged from the cooling system when changing components...

Hmm they said they “flushed” it and replaced the coolant. I would assume that means they burped it. But maybe there was some nuance to the way that burping is performed?

 

[Rhetoric]

Hmm they said they “flushed” it and replaced the coolant. I would assume that means they burped it. But maybe there was some nuance to the way that burping is performed?

I would ask exactly what was done without leading them on and divulging what the proper procedure is.

A full flush would mean they replaced all 16.3 quarts (4.075 gallons) of coolant. Which also means they used the block drains to drain it all.

Again. Just a hypothesis. But since you are looking for an answer... here we are.

 

[2001LC]

I've never have had to replace ECT sensor. In the 99-02 we've two ECT sensors next to each other. 1 for dash gauge, 1 for ECM.

I think @Rhetoric nailed it. Low coolant.

I see this time and time again. When just radiator drain, not much air in system. But when block drained, as it should be. We get lots of air. Blowout the system clearing heater cores, we get even more air pocket.

We must fill system. Bring up to operating temp and 3K RPM for few minutes. Shut down and let sit cooling overnight. Best parked front end higher than rear. Check under radiator cap and top, before starting or sun heats the air. Repeat each day, until level under cap found max.

When coolant to low, the ECT (engine coolant temp) sensor is out of coolant and reading air. The sensor rides high in the engine coolant system. So system need not be very low, for sensor to be out of coolant. We then get a false, cool reading, on dash water temp gauge.

Also, if to low. Coolant doesn't make to the heater cores, for cabin HVAC heat. We get warm air rather than hot, from HVAC vents.

We also must have the correct thermostat (OEM best) with jiggle valve. Jiggle valve must be at top. It part of the way system bleeds off air.

Cap and reservoir must also be to spec.

Smell of coolant in a low system. Then crank no start. Are bad signs.

 

[2001LC]

My bet, INDY shop that works on all makes and models.

 

[tiomateo]

I've never have had to replace ECT sensor. In the 99-02 we've two ECT sensors next to each other. 1 for dash gauge, 1 for ECM.

I think @Rhetoric nailed it. Low coolant.

I see this time and time again. When just radiator drain, not much air in system. But when block drained, as it should be. We get lots of air. Blowout the system clearing heater cores, we get even more air pocket.

We must fill system. Bring up to operating temp and 3K RPM for few minutes. Shut down and let sit cooling overnight. Best parked front end higher than rear. Check under radiator cap and top, before starting or sun heats the air. Repeat each day, until level under cap found max.

When coolant to low, the ECT (engine coolant temp) sensor is out of coolant and reading air. The sensor rides high in the engine coolant system. So system need not be very low, for sensor to be out of coolant. We then get a false, cool reading, on dash water temp gauge.

Also, if to low. Coolant doesn't make to the heater cores, for cabin HVAC heat. We get warm air rather than hot, from HVAC vents.

We also must have the correct thermostat (OEM best) with jiggle valve. Jiggle valve must be at top. It part of the way system bleeds off air.

Cap and reservoir must also be to spec.

Smell of coolant in a low system. Then crank no start. Are bad signs.

This is the most thorough answer I could have possibly dreamed of. Thank you @2001LC
I know that it only took them about an hour, so it definitely didn’t sit overnight with the front end inclined.

 

[Bisho]

I had to replace a coolant sensor…when I mashed the top of it with the intake manifold when replacing the starter.

 

[2001LC]

This is the most thorough answer I could have possibly dreamed of. Thank you @2001LC
I know that it only took them about an hour, so it definitely didn’t sit overnight with the front end inclined.

Was this and INDY shop, that works on all makes & models, with good prices?

Check engine light (CEL), means system detected trouble code (DTC). What was the code?