3.0L Temp Sending Unit Diagnosis

[barthel]

Afternoon All, and Happy Easter.

I had my boat out for the first time yesterday ('98 Stingray 180RS, 3.0L, Alpha 1 Gen II). Most things went well, but I noticed the temp gauge wasn't working. Well, did some reading here and did the first basic checks, I'm just looking for someone to confirm my thinking.

Tested the gauge, grounded the wire and turned the boat to run, it pegged high (and strangely enough is still there). Did a continuity check, everything seemed to check out OK there. Checked Ohms between post and ground, got 900 or so. Checked ohms between post and sender body, got about 700 or so. Checked ohms between body and ground, nothing.

So, does this mean I'm not grounded or is the sender bad? I've only had the boat a few weeks, the sender looks original (no teflon tape or permatex).

Any help would be appreciated.

P.S.
Should I be concerned that gauge is still pegged?

 

[Don S]

Re: 3.0L Temp Sending Unit Diagnosis

To test the gauge, you remove the temp sender wire from the temp sender. Then, with the key on, you touch the wire to a good ground for for a quick second to see if the gauge pegs or not. If you leave it on too long you can damage the gauge.
With the sender wire removed from the sender and the gauge, check do an ohms check on the wire. Should read near zero

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

If you leave it on too long you can damage the gauge.

How long is too long Don? I only had it on for a few seconds, long enough to see it peg then turned the ignition off again.

Checked ohms and continuity from the back of the gauge to the sender termination. Continuity was good, ohms were .1

 

[Don S]

Re: 3.0L Temp Sending Unit Diagnosis

How long is too long Don?

Have no clue, never left one hooked up for more that a split second. Have you tapped the gauge to see if it just stuck there temporarily?
Here is how you test the sender. Make sure you are testing the temp sender and not the alarm switch.


View attachment Testing temp sender.pdf

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

Yes, tried tapping on it, banging on it and even loosened everything up. It moved a bit, but hasn't come back the other way. Looks like I'm buying a new gauge too.

Took the sender out and tested it the way you showed, although I used a heat gun. At 240 degrees it has about 200 ohms of resistance. It changed as it got hot, but never even approached the number on that TSB.

I'm fairly certain I got the sender, it looks the same as in all the pics of them, it was on a block right under the thermostat housing. There is space for a second sender it looks like, but there's a plug in there.

 

[Don S]

Re: 3.0L Temp Sending Unit Diagnosis

The temp sender should have a tan wire to it, the alarm switches have tan with a blue stripe wire.

Anything over 140 ohms is going to register cold on a gauge. Have you hooked the sender and gauge back up to see if the gauge drops?

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

Then that would be the one as it had a tan wire connected to it.

I did connect everything back up and turn the boat on, the gauge didn't budge.

So, beside the gauge that I apparently fried, I should replace the sending unit?

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

UPDATE:

Well replaced the sending unit, and it STILL doesn't work. I got the gauge to zero out again, but it only moves off of 120 about an 1/8 of an inch. Is there any way that my engine is actually running that cool?????

Thinking not, I'm pretty sure my next stab at the problem is going to be the replacing the gauge. Everything else seemed to check out OK.

Thoughts?

 

[fat fanny]

Re: 3.0L Temp Sending Unit Diagnosis

I have had this issue before as well but I didn't fry my gauge. Double check the continuity of the tan wire there could also be a break in the wire, do not use any teflon tape and or paste on the sending unit, make sure all wire connections have an ample amount of dialectric grease, and you might as well change the stat while ur at it to rule out the last piece of the puzzle besides the most obviuos culprit the gauge.

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

No, I did not use teflon tape on the sender, I read enough here to know that was a no-no.

I checked the wiring when I had it apart, continuity and resistance were both good on the sender wiring and used D-E grease when i put it all back together. I have not changed the thermostat, but didn't really think that could produce "not" getting a temp reading even if the stat had been removed. When I hook it up to muffs in the driveway, the exiting water is warm, but not that warm.

 

[achris]

Re: 3.0L Temp Sending Unit Diagnosis

The sender and gauge are 33-240 ohm units. That is, at cold the sender will be 240 ohms, and the gauge will show COLD (gee, what a surprise ). At 'full' temperature (about 250 degrees) the sender will have dropped resistance to 33 ohms, and gauge shows HOT....

HTH,

Chris........

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

That is, at cold the sender will be 240 ohms, and the gauge will show COLD (gee, what a surprise ). At 'full' temperature (about 250 degrees) the sender will have dropped resistance to 33 ohms, and gauge shows HOT.... .

Yeah, the "old" sender was showing upwards of 399 cold, so I'm fairly sure it was bad. Even getting it to 240 degrees with a heat gun only dropped to to the 150's ohm wise.

 

[barthel]

Re: 3.0L Temp Sending Unit Diagnosis

UPDATE II:

Well, I replaced the thermostat and miraculously the temp gauge now works!

Thanks all for your help.