2000 QX4 Temp Gauge issues?

[jiannichan]

Hello everyone. SO I am having a problem with the temp gauge on my 2000 QX4. When I drive the temp will some times drop down below the C and then rise up to normal range when I stop...and will drop down again when I'm driving. When I drive for a prolonged period without stopping, it will come up and sit at the normal range, which I guess is a little below halfway. I have attached a video of it happening yesterday. I have already purchased a new thermostat as well as a new radiator. Some times I can smell coolant when I get home but I don't see any leaks anywhere that I can see but will check again. Car drives perfectly fine, when I come to a complete stop and the car is idling, I can barely tell that it is on. Overall the engine itself is great. As you can see in the video, the car has 223,xxx miles on there. I am the second owner of it and the first owner is a friend of the family that we have known for years and I know he takes great care of his vehicle. Just wanted to share a little background.

Turn off the sound if you want to ignore the music
https://youtu.be/9kE7ShFeJjc

Thanks in advanced for any and all responses/advice/suggestions.

jchan

[atraudes]

First things first, check the coolant level and verify there aren't any leaks. A good way to check for leaks is to drive it around till it's warmed up, then park it and throw a large clean piece of cardboard underneath and let it idle for a few minutes. If you have to fill it up, keep checking and refilling until the level doesn't go down any more.

It really sounds like a bad thermostat since that's exactly what one that's stuck open will do. However, I've read a few accounts of the temperature sensor actually being at fault in cases like this (they had already replaced the thermostat, just like you). Fortunately for you, the sensor is right up front and a new one can be had for less than $20.


(It's the thermal transmitter. Image pulled from EM-10 of the FSM)

If you get through all that and still have problems, pull the thermostat back out and follow the FSM's steps for verifying that it's working properly (suspend in a pot of boiling water, make sure it opens, etc.)

By the way, I'm jealous that it's running so well with so many miles. Here's hoping mine will be as happy in 50k miles

[fueler]

Thermostat stuck open, or possible stuck or sticking fan clutch. Does the fan sound like a school bus when you drive?

Never heard of the thermal transmitter issue.... interesting to know. Thanks

[rgk]

I've been wondering what that school bus sound was, I always thought it was the swirl control valve activating. It seems to happen sometimes on startup and often at very high ambient temps, like 95F+.

[atraudes]

Oh, you're talking fan going full bore like a single engine plane taking off? I replaced my fan clutch and it does that too. I heard pretty much all aftermarket ones do for whatever reason. It should go away pretty quickly (<30 seconds)

[jiannichan]

Okey, so I cleaned out the radiator top, since it was fill of white dust and such. Drove the car around until it warmed up (after doing the up and down thing on the gauge until it finally stayed at normal operating range..just below the middle). I saw hairline crack on top about 5 inches long with some fluid coming out. Level was fine when I checked...maybe slightly low but not abnormally low. I just changed out the radiator since I had already purchased one anyways this morning. I refilled it with some 50/50 Asian from Oreilly (recommended by them). When I drained out the coolant to swap, the two bottom tubes had some red slightly thicker fluid coming out. What is that? Anyways, the car ran fine for about 15 minutyes and then kept doing the up and down thing again with the gauge...quite disappointed. The fan does kick on when the car is at a complete stop but then turns off. I do also notice that the car never goes above middle range on the gauge when I drive, even after I drive the car on 100+ mile round trips. (from Plano to Oklahoma and back fishing trips)

I do have a thermostat that can replace it with but I am having trouble finding out the location even when looking at the FSM. Is it when you follow the bottom tube, up to behind the fan? Held in by what appears to be 3 bolts 12mm? If so, that looks like it'll be a b*** to get to.

[jiannichan]

Thermostat stuck open, or possible stuck or sticking fan clutch. Does the fan sound like a school bus when you drive?

Never heard of the thermal transmitter issue.... interesting to know. Thanks

I do not recall ever hearing the fan come on while driving but it does come on when I sit at a stop for a long time...rarely ever comes on when at a stop light though. Usually when I am parked waiting in a drive through or gas station. It is pretty loud when it comes on but it only runs for a short time.

[atraudes]

When I drained out the coolant to swap, the two bottom tubes had some red slightly thicker fluid coming out. What is that?

The red fluid is the transmission fluid. The radiator has a built-in transmission cooler. One of the reasons they're combined is the engine coolant helps warm the transmission fluid quicker on cold starts. The send and receive lines for the transmission fluid are the two smaller lines near the center on the bottom. If you drained any significant amount of fluid this time or when you changed the radiator, check the fluid on your transmission to make sure it's within range.

[jiannichan]

Thanks!!

[csmith99]

Just had a similar issue. The mechanic wanted to replace the temperature sensor. That didn't work, then he replaced the fan, that helped a little, then he replaced the $20 thermostat and that fixed it. I would suggest going in the reverse order.

[jiannichan]

When I drained out the coolant to swap, the two bottom tubes had some red slightly thicker fluid coming out. What is that?

The red fluid is the transmission fluid. The radiator has a built-in transmission cooler. One of the reasons they're combined is the engine coolant helps warm the transmission fluid quicker on cold starts. The send and receive lines for the transmission fluid are the two smaller lines near the center on the bottom. If you drained any significant amount of fluid this time or when you changed the radiator, check the fluid on your transmission to make sure it's within range.

Car runs great now. Issue appears to have gone away on its own. Problem I have now is the car is leaking transmission fluid from the line attached to the radiator. Not sure of it is the house that's the issue or the actual metal inlet on the radiator itself. Everything appears to be tight. I have read that you may need to take it offthe metal nipple and add Teflon tape to the threads? Anyone else have had this issue after replacing the radiator? I've already changed out the ring clamp with the kind that you screw to tighten. Will try a new hose next as soon as I can find an auto store that has one in stock.