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Old 07-16-2019, 11:41 AM   #1
MisterBLC
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Default Coolant Temp Threads Messed up - Repair options in PDX

So frustrated! Went to fix a weeping coolant temp sensor on my wife's '94 940T. The head was previously rebuilt and I had the shop install new sensors (I think the head I used originally had the early style 1-wire sensor...converted to the later 2-wire sensor). However, apparently the shop cross threaded the sensor so when I went to tighten it, the sensor just popped and spun easily. Pulling it out, the sensor was clearly cross threaded and new sensor when spun in go in cock-eyed and won't tighten

Sensor: https://www.ipdusa.com/products/7209...ge-swf-1362645

Looking for repair options. I think my best bet is some sort of helicoil solution (threads are M16x1.5)...but repair kits are expensive. Anyone in the PDX area have one I can borrow? Any other alternative solutions I am not thinking of?

Thanks!
Brian
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Old 07-16-2019, 12:16 PM   #2
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I wonder whether wrapping teflon tape around the threads would solve the problem?
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Old 07-16-2019, 12:36 PM   #3
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Are you sure the sender is in the correct hole? It should be in #2.



The temp sender has 5/8"-18 threads but they don't do the sealing. The beveled part below the threads is what seals the sender.



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Old 07-16-2019, 02:29 PM   #4
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Yes, right spot just above the knock sensor.

The threads are straight threads...tape/goop isn't going to work as the threads aren't the sealing point...the tapered seat should be what seals the sensor.
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Old 07-22-2019, 07:06 PM   #5
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Ok update...so I didn't get a good pciture, but apparently the old style 1-wire sensor was not as deep as the new style 2-wire sensor. Both are the same threads, so when the machine shop installed the new 2-wire sensor in the head, it only engaged the outer 2 threads or so, which were the ones damaged. I bought an old-style 1-wire sensors, cleaned up the threads remaining in the head with a tap, and was able to install the 1-wire sensor in the head successfully! Now I just need to modify the gauge wiring so that the 1-wire sensor causes the gauge to read correctly...currently it reads hot. Does anyone know the specs on these two sensors to help me fix up the reading?
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Old 07-22-2019, 08:42 PM   #6
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Does the gauge work at all? Maybe the second wire needs a ground point.
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Old 07-22-2019, 09:14 PM   #7
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Quote:
Originally Posted by MisterBLC View Post
I bought an old-style 1-wire sensor
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Originally Posted by lummert View Post
Does the gauge work at all? Maybe the second wire needs a ground point.
I'd like to know which "old-style 1-wire sensor" he stuck in there. Probably for a 240, which used a 1-wire right to the end of its pitiful life, using the head as a ground. My diagrams say 7/9's all had 2 wires directly from the gauge in a long loop, with the sensor inline, no separate ground required.

240



7/9

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Old 07-22-2019, 11:28 PM   #8
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It looks like the sensor you labelled 240, but its for very early 7's as well...my '85 740 turbo uses it as well. IPD puts this as a 7xx sensor:
https://www.ipdusa.com/products/5907...t-vr850-460191

Gauge does work, but fully warm moves the 940 gauge past center...when the fan kicks in, the gauge is almost to the red. I did need to ground the other wire, otherwise the gauge would move with the blinker!
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Old 07-23-2019, 01:38 PM   #9
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OK another update: the car has a new idle problem that did not exist before this issue with the coolant sensor. Now, as the car heats up and the gauge moves above the midpoint, the idle will slowly drop and drop until the engine almost dies. This behavior seems to go away when the coolant gauge is completely disconnected, although I only tested this once so I'm not 100% this is the case. I did a full smoke test to ensure we didn't introduce any new vaccuum leaks during the removal of the intake manifold to repair the sensor and found nothing. How could the coolant gauge wiring affect idle? So wierd

I also found that turning the headlights on(!) causes the gauge to read much higher...there is some electrical ground loop going on that I don't understand.
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Old 07-23-2019, 01:43 PM   #10
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On latter 7/9s i wanna say the temp gauge is 2-pin and shares a grounding point on the intake manifold that is also shared by the engine coolant temp sensor?

It's rare, but once in a great while I've seen one of the little wire-crimps that holds the multi-ground bundle come loose on 1993-1994 cars if yours is one of those (mom's 1993 244 has that issue & I get to take the engine harness apart/replace it with a non-defective one now that I found all my decent crimper tools).

Kinda sad as 1993-1994 tend to be mostly good years with even some good japanese parts, but with a bit of odd electrical on some.

Having said that, assuming there are no vacuum leaks, the later 2.4 cars seem to idle a bit lower warm and hunt a bit with the 02 sensor switching? But it shouldn't almost die in good repair assuming the throttle position switch/throttle body is clean/adjusted properly.

Good luck.
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Old 07-24-2019, 01:10 PM   #11
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Kjets, are you talking about the crimps on the eyelets for the grounds at the fuel rail? Or are there also crimps elsewhere in the engine wiring harness that go bad?

Throttle switch is definitely correctly adjusted and throttle is reasonably clean...wouldn't hurt to spray a bit in there though as well.
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Old 07-24-2019, 01:38 PM   #12
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More than one ground wire is often joined together into 1 branching out with a crimp under the intake much like the injector wires.


That’s a real outside shot though.
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