Alrighty,

First let me start by saying I am new to this forum but not to automotive forums in general. I tried to look through existing posts as to not create another thread but many threads contradicted each other and most were so old there wasn't a point in replying.

That being said I have a 2004 Land Rover Discovery II. I have owned it for about a year and it currently has 88,000 miles.

A few weeks ago I noticed my car was leaking coolant. I traced the leak to a crack in the expansion tank. No surprise there, it happens. So I made the mistake of thinking I could just plastic weld it to fix. No such luck. My dad was driving the truck from Ft. Bliss to White Sands Missile Range (30 miles) When the car overheated. I had to go get him and towed him and the truck home with a 550i (see pic for a good laugh)

Anyway, I bought a new expansion tank and replaced it. Now when you turn the key to accessory or start it, the coolant gauge overheat light comes on (red) and the gauge goes all the way to hot and then drops down to cold.

From what I understand, this usually means that the coolant temperature sensor is bad. I also understand there are two sensors? One to the gauge and one to the ecu? I replaced the one that is on the passenger side of the radiator at the bottom. The gauge is still showing the error. So now I want to change the other sensor. The only problem is I can't find any graphic or info online as to its location. I think I have located it but its nearly impossible to get off without removing other crap and I would like to make sure its the right sensor before I go through all the trouble.

I'm also wondering if it is possible that the thermostat went bad during the overheat and if that could be tripping the light and causing the gauge issue?

Lastly I found a 3 year old thread in which someone said they had to reset the coolant overheat light? By the way there are no other lights on and the engine will run fine though I haven't let it run more than a minute because I am worried about it overheating.

Any Ideas, suggestions, advice?

Thanks in advance.

Pic 1 In tow.
pic 2 Where I think the sensor is.
pic 3 The sensor they gave me for the bottom of the radiator wasn't the right one obviously. Anyone know what the heck its for out of curiosity?

 

Have the codes checked. I was working on a guys 2004 Disco that he had overheated and after fixing the problem and bleeding the coolant was having the same gauge issue. His vehicle had a code for engine temperature out of range (or something similar) because there was no coolant in contact with the sensor after it had overheated. I cleared the code, and the gauge went back to normal.

Picture 2 is the ECT sensor which both operates the gauge and gives parameters for engine management in the ECU

 

Rookie mistake! I hadn't given a lot of thought to having the codes checked because in my other cars anytime there is a code to read the check engine light will come on. Ill have to go pick up a OBD scanner as I usually just drive to an auto parts store and borrow one.

I'll go buy one today and do a check and see what comes up and if clearing it helps.

Thanks for the input!

 

Just got home from work and scanned for codes and got "P0118 engine coolant temperature circuit high input"

From what I've read this is for the sensor I haven't yet replaced. Anyone have any tips for getting this sensor off? There's a strip of metal directly behind the bolt that's too close for the head of a socket to slip over the bolt :/

I'm going to try to clear the code and let the engine run and watch it with a laser thermometer and see if it's all good now or if I do indeed need to replace the sensor.

 

that strip of metal is a support bar connecting the fuel rail. have you taken the plug off and tried a deep socket yet? if so try a crowsfoot.

 

If the code returns after clearing it, you might also want to check the wiring going to that sensor. If my memory serves right, the loom for that runs down the front of the engine behind the accessory brackets and it prone to becoming brittle.
P0118 is a short to ground per RAVE. Perhaps the insulation on the hot wire is worn through and is touching something?

 

The temp sensor in the radiator is for the secondary air injection (SAI) system. It tells the computer that the coolant is cold and that the SAI needs to run if truck is just started. Your problem is related to the sensor in the manifold.

 

@drowssap

I had already tried a deep socket the problem is the thickness of the socket head they don't make them thin enough for the clearance. I had never seen a crows foot before but that would definitely work. ultimately didn't need it though!

@lordmorpheus

the code didn't return after clearing it. I just unplugged the sensor and sprayed it with some cleaner and then reconnected it. I had also ordered a new thermostat just in case that was the issue and decided to replace the old one anyway. Buttoned it all back up and drove her today and its all good as normal. There was a p0305 code that came up but I cleared that and haven't had any issue since. So ill keep an eye on it.

@04duxlr

yes the error code was for one sensor but the gauge issue was for the other sensor as I understand it. Ultimately I did not have to replace the sensor in the manifold and I think the sensor in the radiator was probably fine but for as cheap as it was and given that id already swapped it out I just left it.

Thanks for all the help! Good as new.

 

My understanding of the operation of the coolant temp sensors and the SAI was not correct. Thanks to a member of this forum, jafir, I have been set straight. Based on a combination of previous threads, incorrect parts descriptions from vendors and assumptions based on radiator listings I was under the impression that the temp sensor in the radiator controlled the SAI. This is not the case. Should have read RAVE and the BOSCH ECU manuals cover to cover.


The SAI operation is controlled by the temp readings from the intake manifold sensor. The sensor in the radiator is only used by the computer to check for a stuck thermostat. It compares the temperature readings of the two sensors and if it exceeds certain parameters then it concludes the thermostat is stuck open and generates a code P0126. If tests of the radiator outlet sensor indicate that it is not functioning correctly, codes P1118 or P1117 will be generated. This radiator temp sender was added to the management system at the same time that SAI was introduced so if you have SAI coincidentally you need a radiator that has the port for the sender. Hopefully this post will help keep someone from coming to the same erroneous conclusion that I did.

 

Because of all the mis-information in other threads is exactly why I had to start this one! And yes hopefully this will help others in the future.