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Ok team... heres another weird one. 

I have a customers 03 LL bean H-6 engine. 

Car arrived with an over heating issue from a bad headgasket job. I could drive the car about a mile and then it would overheat and start blowing steam etc. 

So we replaced the engine with a JDM unit and when i went to drive it the temp gauge shot to normal temp by the time i had driven 25 yards.  by the time i had driven 1/8 mile it had pegged in the hot. 

Knowing that the engine cant get that hot that fast i then grabbed my scan gauge to see what the computer was reading. it was reading 246 deg ( which is as hight as that goes).

The car is not hot. i was able to take the radiator cap off and there wasnt even any pressure built up...

I swapped in a couple different coolant temp sensors to see if that helped.... same result. 

I then pulled a forester up that has the same sensor and made a jumper wire  and used a jumper cable to ground the 2 cars . Now the forester was able to read the temp of the H6 engine. The gauge read normal operating temp and the computer was reading 189 deg.  now we know the engine is fine and the sensor is fine. 

This feels/acts like a bad ground. when you turn the headlights on the gauge moves. When you turn the turn signal on the gauge fluctuates. When you rev the engine the gauge moves. 

I pulled up the wiring and it seems real simple: one wire goes directly from the sensor to the computer, one wire goes to the gauge and the 3rd wire seems to be a ground for several thing including the computer. 

Just wondering if anyone had seen this and where to start. 

Thanks,

Craig

 

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I can't recall all the grounds but certainly, with an engine swap, it would be easy to miss 1 or 2 so, double check the straps to the intake mani, the grounds on the dogbone at the firewall area, the strut tower, I think the frame under the radiator?

Also wondering if a bad wire in the body to hatch gaiter could cause some weird ness?

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yeah i was going to go the computer and add a jumper wire off the ground wire to see if that corrects it. 

You talking about the wires that break in between the body and rear hatch from repeated opening?

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1 hour ago, logic23 said:

...I then pulled a forester up that has the same sensor and made a jumper wire  and used a jumper cable to ground the 2 cars . Now the forester was able to read the temp of the H6 engine...

Nice bit of sleuthing! I'm impressed

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8 hours ago, forester2002s said:

Nice bit of sleuthing! I'm impressed

yeah ive learned over the years how to eliminate the big things quickly ... this was the first time i had done this :) 

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9 hours ago, 1 Lucky Texan said:

I can't recall all the grounds but certainly, with an engine swap, it would be easy to miss 1 or 2 so, double check the straps to the intake mani, the grounds on the dogbone at the firewall area, the strut tower, I think the frame under the radiator?

Also wondering if a bad wire in the body to hatch gaiter could cause some weird ness?

not likely to mess with engine related stuff... the other half's 06 LL Bean had a BUNCH of broken wires in the rear hatch junction... no rear defrost, rear wiper, license plate lights, etc.. all gauges and engine stuff were fine.

But definitely agree about going back thru the engine bay and double or triple checking all connections & grounds - the gauge acting squirrely with turn signals & what not definitely indicate a problem somewhere

 

 

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so sometimes you get lucky >

The issue was that someone had spliced in a new coolant temp plug and wired it wrong... on the H6 there is one wire thats the same color as the H4. its a white with blue/green stripe.

The issue is that its a different wire/ position on the plug.  rewired correctly and ECU and gauge are both functioning properly. 

The splice was under the intake so it was hard to see it... like i said... sometimes you get lucky. 

Thanks y'all for the input

Craig

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