95 Four Winns 5.0

[joey nathan]

Hello All,
Trouble is VDO temperature gauge laying on zero when running with new thermostat; and grounding the brown wire on the manifold causes gauge to deflect full scale.

Is sending unit p/n 3853787 correct for this engine? (OMC 502 APHUE)

https://www.ebay.com/p/OMC-Temperature-Sending-Unit-PN-3853787/1530321935?iid=302305319653

Unit on the engine now has a spade lug connection, and this shows a nut/lock washer like for a ring terminal? Does that mean it's wrong sending unit?

 

[alldodge]

Unit on the engine now has a spade lug connection, and this shows a nut/lock washer like for a ring terminal?

The part number listed and the part on ebay show the correct part. The part number crosses to Merc 806490T so it should be the right one. A sender with a spade lug is not the same part number, so I would contact seller first.

Does that mean it's wrong sending unit?

Its not the right part but still may work. Is the thermostat housing good and warm to the touch?

If it is, remove the sender and place an ohm meter on the threads and on the spade terminal. Place in a pan of water on the stove and heat the water up. You should see 240 ohms when cold and about 33 ohms when hot

 

[joey nathan]

Thank You Sir,
I have some more troubleshooting to do...

BTW, how do I contact forum administrator, I need to update log-in and password for new e-mail

 

[alldodge]

Send a PM to GA_Boater or iboats_tim

 

[GA_Boater]

You logged in to make this post with your old info, so you can update your email by clicking your Username on top and then click Edit Profile. Scroll down to to the E-mail box, change your password and make sure you click on Save on the bottom.

Your Username and Password will remain the same and so you won't have to change them, joey nathan

 

[joey nathan]

That's where I get hung up - need old password which is just a series of dots. It's been so long I don't remember what it was? Tried copy and paste but it doesn't bring the password over...

 

[joey nathan]

Okay, thanks I got it changed that time

 

[joey nathan]

So, I've replaced the temp sensor and now the gauge is 95% full scale at operating temp?

It measured 550 ohms cold btw.

Pretty sure this is correct part for this engine (Sierra 18-5897) so I'm at a loss as to why a) the wrong sensor was in there to begin with - which worked for years, and b) why the huge discrepancy in the resistance value?

Scratching my head a little on this one...

 

[alldodge]

While 550 ohms is not bad cold, the spec should read 330 ohms.
Sierra buys/sells boat parts, are they as good as higher dollar, sometimes yes, some no, I'm in the no category.

What is the ohm value when it reaches 180 degrees (pan of water on the stove)?

 

[joey nathan]

Well I'm at a loss here - went out and got the OEM part 3853787 and it is even farther out from the spec cited This one measures 850 ohms cold and 195 ohms in boiling water.

What don't I understand here? I haven't put it in the boat yet, but does this part have any chance of working correctly, i.e. putting the gauge in the middle at operating temp?

Haven't checked the Sierra part in boiling water yet, but it's not the right one either as it puts gauge at 95% at operating temperature...

 

[alldodge]

With it reading about the same as the old, and peg full scale when cold, the wire going to the sender may be shorted to ground. If it reads cold without the wire attached, then we can say that part is correct.

I don't get the resistance readings other then maybe your meter.

 

[Bt Doctur]

The sender may be specific to the VDO brand

https://www.vdo-gauges.com/sensors/t...nsor-only.html

https://www.jegs.com/p/VDO/VDO-Tempe...70966/10002/-1

 

[joey nathan]

Thanks for input all...

Using a Fluke DMM for troubleshooting. Taking wire from transducer and grounding it to the engine pegs the meter - seems to indicate that both wire and meter are good, no?

What's confusing to me is OMC listing this as an "OEM" part when it really calls for VDO specific?

 

[alldodge]

Taking wire from transducer and grounding it to the engine pegs the meter - seems to indicate that both wire and meter are good, no?

Yes, that's the way it should react

 

[joey nathan]

Wanted to follow up and thank all who helped with advice. Boat is ship shape now.

Still puzzled by the temperature sensor issue however. The OEM part works but the resistance readings much different than that quoted. OMC #3853787 checked 850 ohms cold and 195 ohms in boiling water but gauge goes center scale at operating temperature. Just an FYI...