Water Temp. Gauge

[drewchips]

I have a VDO Water Temp. gauge on my '98 Four Winns Horizon QX. The boat is powered by a '97 Volvo Penta SX Cobra, 3.0 liter, 135 hp. This I/O has a raw water cooling pump. The problem I am having is the water temp. gauge never reads above 100 degrees. The range on the gauge is from 100 to 250 degrees. It never really moves past the minimum reading. I have replaced the sending unit and have also tested the gauge by grounding the wire on the sending unit and turning the ignition to the start position. The needle pegs at the maxium reading so I know the gauge is working. Also, when the key is turned to the start position the needle moves just a bit to the lowest reading (i.e. 100 degrees) but no matter how long I run the engine it never moves past 100. Should I be concerned? I don't know what else to look for if the gauge is working and the sending unit is brand new.<br /><br />Thanks!

 

[J.J.W]

Re: Water Temp. Gauge

Chances are the thermostat is stuck open. I've even seen little pepples get wedged in blocking them open.<br />Good luck,<br />Justin@sterndrive.cc<br />www.sterndrive.cc

 

[drewchips]

Re: Water Temp. Gauge

Thanks for the reply. If that is the case, would the thermostat just need cleaning or would it need to be replaced?

 

[Boatin Bob]

Re: Water Temp. Gauge

Did it ever work correctly? Could it have the wrong sender in it and you replaced it with same? Could you have some corrosion on the connections affecting the resistance of the wire? If you go the t-stat route then I would just replace it since you will have it apart and probably need to replace the gasket anyway. <br />ps...if the t-stat is really the problem your not doing your engine any favors by running it this way as it's not being allowed to come up to correct operating temp.

 

[drewchips]

Re: Water Temp. Gauge

Boatin Bob - it appears attempted to reply to my topic hear, but for some reason your reply does not appear. I am very interested in any insight you can provide as well. Thanks for your time.

 

[drewchips]

Re: Water Temp. Gauge

Boatin Bob - Your reply just appeared. Thanks! I am the second owner and do not remember it working correctly, but I did replace it with the OEM part from an OMC/Volvo parts dealer. The connections appear to be fine - no corrosion.<br />I will replace the t-stat and see what happens.<br />Thanks again!

 

[cobra 3.0]

Re: Water Temp. Gauge

You can check the t-stat in a pot of boiling water with a cooking thermometer. It should open at 160 degrees.

 

[drewchips]

Re: Water Temp. Gauge

Thanks Cobra. I'll give that a try before replacing it.

 

[Boatin Bob]

Re: Water Temp. Gauge

Just re-read your first post again, so the guage starts at 100 and the needle doesn't really move, I would think a stuck open t-stat would still move some after a while but it would be very slow. You have proven out the gauge and as long as you have the correct sender in there. When you grounded out the gauge before, did you do it at the gauge or using the sending wire at the block?

 

[Boatin Bob]

Re: Water Temp. Gauge

I'm having problems posting on this board today so if this is a duplicate, I'm sorry. Anyway about the sender, did you put any sealer or teflon tape on the the threads because that can act as an insulator and the sender may not work properley.

 

[drewchips]

Re: Water Temp. Gauge

I did use teflon tape on the threads as that was how the previous one was installed. If that acts as an insulator, I will remove the tape and see what happens. That had not occured to me. It seemed to make sense to use the tape as I have some experience in plumbing and that is how those types of threads are typically sealed.<br /><br />The guage starts just below 100 degrees and moves up to 100 when the ignition is switched on. After that it doesn't move at all. When I grounded out the gauge, I did it using the sending wire at the block.

 

[TwoBallScrewBall]

Re: Water Temp. Gauge

I have no T-stat in my 3.0 and still run about 140-160, closed cooling though.....

 

[Boatin Bob]

Re: Water Temp. Gauge

Sounds like the gauge and wire are OK, could be the tape on the sender, those are supposed to be a tapered thread so no sealer is required.

 

[drewchips]

Re: Water Temp. Gauge

Good to know. Thanks. I will remove the tape and see what happens. I'll let you know what the result is.

 

[gaugeguy]

Re: Water Temp. Gauge

I think Bob has hit the nail on the head. The teflon tape isn't "insulating" the sender, it is actually inhibiting the ground connection between the engine and the body of the sender. If that ground connection isn't there, the sender is basically "open", and the gauge will never read above its minimum setting.<br /><br />The threads are brass and tapered designed to be leak proof.

 

[drewchips]

Re: Water Temp. Gauge

Wonderful! Thanks to everyone for your input. I will let you know what happens when I take it out this weekend.

 

[merc200]

Re: Water Temp. Gauge

drew-take an ohm meter and see if the sender is getting ground. I bet the tape is NOT preventing the sender from getting ground. Just because threads are tapered, doesn't mean that they won't leak. I used liquid pipe sealant on mine and it gets ground just fine. I think your problem is somewhere else..........

 

[drewchips]

Re: Water Temp. Gauge

Thanks for the advice re: the thread sealer. I took the temp. sending unit out and the threads are so sharp that I think they would have cut through the tape and grounded the sending unit anyway. While in that area though, I decided to remove the t-stat housing. I came to discover that there was no thermostat! The previous owner (or mechanic) had removed it! I am obviously going to replace it but now my question is, why would someone do that? Also, what unforseen damage should I be aware of/look for since the t-stat has not been in the engine for quite some time? I bought the bought last summer and ran it for about a month and a half before winterizing it. There is no telling how long before that the t-stat was removed. I'm baffled here.

 

[merc200]

Re: Water Temp. Gauge

Pretty much the only thing you will notice from a cool-running engine is there will be condensation gunk underneath the valve covers; milky looking stuff. Put a t-stat in it and forget about it. I'd take the oil filler cap off and look on the bottom of the cap to see if there is milky gunk there. If there is, I'd think about taking the valve covers off and clean them. It won't hurt anything though.

 

[TwoBallScrewBall]

Re: Water Temp. Gauge

Well, only real problem is that the oil never gets warm enough to burn off condensation moisture, leading to a very small amount of water in the oil. That and the engine won't be running at optimum efficiency at 100 degrees or less. Needs to be at least 140-160. No real damage likely.