False high temp readings and engine harness plug

waughoo · January 26, 2022, 07:15:26 AM

I have been experiencing high engine temp readings of 178 to 190 while at cruiae rpm since I have owned the boat. After a TON of work replacing hoses, thermostats, raw water pumps etc... I was still having the problem.

After a bunch of messing about, i discovered that jostling the engine wiring plug reaulted in movement of my temp gauge reading at the engine panel. This plug is called by many names (gummy bear plug, trailer plug, etc) and is called out in the critical updates section of this website as a "repair this or else" item.

Attached are a few photos of what mine looked like when I removed it.

waughoo · January 26, 2022, 07:18:50 AM

This has been solved many ways by different owners over the years. I happen to like harness plugs as it allows for servicing parts without having to cut and splice electrical connections. I elected to use Deutsch Connectors for my engine harness.

They have a pin that requires a special crimp tool, but I have installed a lot of these about the boat so I feel pretty good about the purchase.

The pins get crimped to the wire end and then inserted into the plugs and sockets. There is a locking tab which keeps them from pulling out under strain.

waughoo · January 26, 2022, 07:22:41 AM

There are two different gauge wires used in the harness so I elected to use one plug for the high awg wires and a second plug for the smaller awg sender wires etc.

The finished harness lives nicely under my coolant expansion tank. The gauge now reads a solid 165 without errant motion. I am so happy to have sorted out that gremlin!

KWKloeber · January 26, 2022, 07:32:21 AM

Alex do you have a product number for the plug set you used?

waughoo · January 26, 2022, 07:59:17 AM

I used the DTP series Deutsch plug for the 10 gauge 12v, gnd and glow, and a DT series Deutsch plug for the remaining sender connections.

Ron Hill · January 26, 2022, 11:40:56 AM

Alex : Just goes to show - what I've been saying sense 1991 !!!!!!

Like I've also mentioned it is easier to just skip any plugs and hard wiring - unless you plan on removing your engine!?!

A few thoughts

waughoo · January 26, 2022, 12:33:45 PM

Yep... it has been said many times and many ways. Just adding my experience to the pile.

Also, I happen to prefer harness plugs. Sometimes being able to quickly disconnect slmething allows access to something else
I am working on in the area. What is it that's said on here all the time... YBYC?

KWKloeber · January 26, 2022, 01:44:27 PM

I think the Deutsch contacts are rated at 25a, but I've heard from a couple owners that with GPs energized they measured the draw at ~30 amp.
Might want to verify that?

Note also that the "current" (uuugh) standard is to use heavy gauge (I use 10) on the S wire (minimize V loss to the solenoid.)

waughoo · January 26, 2022, 04:02:06 PM

Ken,

I figured you were asking with that in mind. The DTP connectors are rated for 25amps. I feel like I looked up the GP current at the time I made the selection for the plug, but now can't recall. Worst case, I could switch to relays for the GP circuit. I have a clamp on meter and will see what I draw on the GP.

I noticed that the CD panels had a #10 for the start solenoid. It seems rather strange in that the start circuit is already a solenoid circuit, but it couldn't hurt. The boat had the old wiring standard with a #10 to send the alt current up to the panel and back down, but it had already been bypassed by a previous owner who installed an external regulator. The #10 is still in the harness so I could just re-purpose that #10 for the start solenoid. I could then use the old start solenoid wire to provide the high temp alarm switch I want to add. CHOICES!!

KWKloeber · January 27, 2022, 09:16:09 AM

Alex
I always thought the GP current should be 18v (6x3) but an owner with brand new NGK plugs it was much higher. It will be interesting to see what you read (of course amps depend on btty voltage as well.) Maybe current varies with temp?

What meter do you have -- I got a Craftsman that does DC amps but the display essentially sucks.
Pet peeve: why do manufacturers continue to call them clamp-ON meters? They are clamp-AROUND meters!!

waughoo · January 27, 2022, 09:25:33 AM

I have a Fluke "clamp around" meter. I it will prob be tested while the boat is plugged into shore power so the btty V will be at their highest possible voltage. I will try and remember to do that when I am at the boat again over the next few days.

waughoo · February 01, 2022, 01:36:22 PM

Ken,

Whep... you were right on the current draw on the glow plugs. The meter says 42amps for about a second or two and then it slowly drops to about 37 in say 15 or so seconds. I guess the relay mod is in my near future as the Deutsch connectors I installed aren't rated for anything that high.

Also, I found out my fluke meter doesn't do DC amps. Thus the Klein pictured. Now I have a good dedicated meter for the boat at least. The Fluke was from my home shop.

Ron Hill · February 01, 2022, 02:07:28 PM

Guys : Another false high temp reading - Will be caused if the metallic covering on the engine cover insolation happens to touch the unprotected temp connection on the thermostat!!!!

That's a reason to install a protective boot on that connection!!

A few thoughts

KWKloeber · February 01, 2022, 04:11:15 PM

Alex

THANKS for that info.

WOW 40 amps is crazy. That's sure not what I had read on (some; somewhere) NGK's datasheet on those plugs. Of course, the data would have been at 10 volts. I bet with a slave relay they'll pull 50+ amps.

I wonder if your plugs are rated 25 disconnect amps (as switch contacts are) or continuous current?

As I always said, adding complexity (e.g., plug connections) can lead to other unintended complexity/potential failures.

Man, that display looks BOSS. MUCH better than my crappy Craftsman display where you cannot read any Mode functions because they are so small. A Klein might be in my future if nothing else because they label it a "clamp meter."

waughoo · February 01, 2022, 08:08:37 PM

Ken,

This boat has the 4 cylinder m35. One extra gloplug is likely to significantly increase the draw. I too was quite surprised.

This Klein was a home depot purchase. I was quite pleased with the display as well. It is completely black and only lights the segments. It is much easier to read than even a standard LCD display with the grey background. The price was only about 90 ish something dollars. Seemed pretty reasonable to me.

I know you aren't particulary fond of the additional complexity of the relay mod, but if you HAD to install ome for an insistant customer, do you have a spec you would suggest? I am thinking of something with a pre made waterproof harness from the automotive sector, but want something with tinned wire.