temp gauge drops to Cold on long climb

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Krazykraut
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temp gauge drops to Cold on long climb

Postby Krazykraut » Mon Jul 02, 2018 10:44 am

So I'm still getting used to all the quirks of my new (to me) 1993 L300 Exceed. It has 205000 km on it, with pretty much everything new in the last year (cylinder head, radiator, transmission, radiator hoses and cap). It runs beautifully and I get 23 mpg with a clean fuel and air filter. I learned on a long mountain pass on a hot day to take it easy, turn off O/D, rev high and let the rest of the traffic swear at me without breaking into a panic.

Yesterday I noticed that the temp needle which usually just sits at 1/4 creep up slowly on a long gentle climb, but then to drop off to "C" completely. The needle never reached 1/2 but even though we were still climbing, just dropped to the cold position. No puffs of smoke, no engine loss of power, the engine was purring just fine. On the downhill following the pass, the needle crept back up to the normal 1/4 position as the engine cooled.

This is odd, as I would expect the needle to climb to "H". Where do I start looking for the issue?
I do have a pyro and boost gauge installed but they seem not to be hooked up. I still need to dive into how to get them connected.

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Growlerbearnz
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temp gauge drops to Cold on long climb

Postby Growlerbearnz » Tue Jul 03, 2018 2:50 pm

My first step would be to replace the temperature sender. What you describe is not your typical faulty sender symptom, but the sender is cheap and easily replaced so it's a good place to start. viewtopic.php?f=94&t=17645
Nothing says "poor workmanship" more than wrinkles in the duct tape.

Krazykraut
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temp gauge drops to Cold on long climb

Postby Krazykraut » Wed Jul 04, 2018 3:32 pm

Thanks Growlerbear! Just as I was driving to Autozone to order the new temp sender, the needle dropped completely to C and doesn't move anymore at all. New probe should be here on Friday. Will go through the troubleshooting steps as outlined. The sender being for both the ECU and the dash gauge, is there a chance that I damage something, driving like this for a day or two? Aside from overheating of course, but I would think the thermostat takes care of coolant temps independently of the gauge.

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Growlerbearnz
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temp gauge drops to Cold on long climb

Postby Growlerbearnz » Wed Jul 04, 2018 4:52 pm

The sensor is two sensors in one package- it's possible the ECU side of it is still working. (It's possible the gauge side is still working too- but it's easy and cheap to swap it out, and probably needs changing anyway if it's as old as the van.)

If the ECU side has failed, you'll have some odd behaviour from the glow plugs and possibly difficult starting. The worst thing that could happen is the glow plugs staying on while the engine is running- that would burn them out pretty quickly. Pay attention to the glow plug relay clicks.

There's a quick test to confirm that the gauge itself is working mentioned in the thread: "To test the connector, I'd find a male spade terminal and plug it into the yellow/red stripe side of the connector. Connect it to engine earth, and turn the ignition on- the gauge should move pretty quickly towards the hot side. Turn the ignition off before the needle reaches the top of the range. That'll confirm if the gauge and wiring are good at least."

If the gauge doesn't move, I'd look for damage to the wiring loom around the sender connector and above the engine. Maybe pull the gauge cluster, trace the lines that go to the gauge, and earth the pin that runs the gauge directly- though that can have consequences if you get it wrong.
Nothing says "poor workmanship" more than wrinkles in the duct tape.

Krazykraut
Posts: 26
Joined: Fri May 25, 2018 10:16 pm
Member's Photo Album: http://www.delica.ca/Photos/
Vehicle: L300 P35W (Apr 1993)
Location: Portland, OR
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temp gauge drops to Cold on long climb

Postby Krazykraut » Wed Jul 04, 2018 4:56 pm

The glow plug relay clicks just fine, engine starts in no time at all and runs smoothly, with no smoke and I don’t hear clicks while idling. I suspect that the ECU side is fine and my wiring is just wonky somewhere.


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Krazykraut
Posts: 26
Joined: Fri May 25, 2018 10:16 pm
Member's Photo Album: http://www.delica.ca/Photos/
Vehicle: L300 P35W (Apr 1993)
Location: Portland, OR
Contact:

temp gauge drops to Cold on long climb

Postby Krazykraut » Wed Jul 04, 2018 6:03 pm

Phew, wiring is ok. After grounding the red/yellow wire and turning on the ignition, the gauge climbs to HOT in 10 seconds or so.
Guess it is the sender after all.


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Krazykraut
Posts: 26
Joined: Fri May 25, 2018 10:16 pm
Member's Photo Album: http://www.delica.ca/Photos/
Vehicle: L300 P35W (Apr 1993)
Location: Portland, OR
Contact:

temp gauge drops to Cold on long climb

Postby Krazykraut » Sat Jul 07, 2018 12:59 pm

Problem solved. The Sender was faulty. I got a new one from Autozone at around US$ 30, swapping it out took about 30 seconds and my gauge is now working fine.
The failure mode was interesting- the sensor would work for ten minutes or so, and then give up, and not work for the rest of the day.

Now to get my pyro hooked up.


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