Lehman water temp sender

Does anyone know the part number(s) applicable to the water temperature sender for a Ford Lehman SP135 using VDO gauges. The sender is available from ADC however I would like to swap the sender out before the weekend and it would never reach me in time. I have heard that it is a common sender and need not be a VDO sender. Hope this is true.
Per infrared heat gun engine runs at 178 degrees. Gauge fluctuates between 180 and 200 degrees. Will creep up from 180 to 200 in 30 seconds then just fall
back to 180. Have checked connections. Also could be wiring or gauge but have been told this scenario likely due to faulty sender.
All help much appreciated.
Thanks,
-David

petdoc4u said:

Does anyone know the part number(s) applicable to the water temperature sender for a Ford Lehman SP135 using VDO gauges. The sender is available from ADC however I would like to swap the sender out before the weekend and it would never reach me in time. I have heard that it is a common sender and need not be a VDO sender. Hope this is true.
Per infrared heat gun engine runs at 178 degrees. Gauge fluctuates between 180 and 200 degrees. Will creep up from 180 to 200 in 30 seconds then just fall
back to 180. Have checked connections. Also could be wiring or gauge but have been told this scenario likely due to faulty sender.
All help much appreciated.
Thanks,
-David

Click to expand...

Does the gauge move up to 200 then fall back to 180 just once as the engine first warms up after a cold start?

If so that is normal.

While a small amount of "overshoot" is normal until a cold engine warms up fully, what you are seeing sounds a bit excessive. I highly doubt that the rise and fall you see is due to a faulty sender or anything electrical if it is at all regular. I would be much more inclined to believe too much air space in the system or a thermostat. I had some of this happening on my Stb engine and a new thermostat fixed it.

Ken

Is the climb to 200, then fall back to 180 only after start? Or does it happen repeatedly?

Either way, easy answer is pull and check, or just replace thermostat and while at it, give the fresh water cooling side a flush if it hasn't had one in awhile.

What Capt Bill says is true in the sense that it happens a lot, but I think properly working cooling ssystems have a little less of a rise and fall, if any at all.

I checked my SP135 parts book and the numbers don't cross reference with anything out there that I can see.

Have you called VDO? Their parts are sold nationally. Here's a spec sheet that may help. It also has a troubling shooting guide for the sender.

https://marine.vdo-gauges.com/media/instructions/A2C59519516 Temperature and Press Senders.pdf

Anything Lehman related, call American Diesel in Kilmarnock, VA.
The founder of the company, recently deceased, is the daddy of the marinized Lehman.
They know that engine better than anyone and can troubleshoot over the phone better than most mechanics can sitting in your engine room.

Greetings,
As well as AD, I've had good dealings with Bomac for Lehman parts.
Ford Lehman Engines | Parts | Service | Bomac Marine

I don't think it's the sender, but more likely voltage fluctuation due to changing loads.
But that's my boat.

Since I know the gauge runs between 172 and 188, while the actual temp stays steady at 156 at the top of the coolant tank, I don't worry unless it goes outside that range.

Thank you for all your input.
Given that the engine did not seem to be overheating but suffering from a bad gauge, wiring or sender, I decided to take a cruise. Initially the gauge crept past 200 degrees only to rapidly fall to 180, this seemed to be an intermittent cycle the first 45 minutes. Over time the gauge settled in just shy of 190 and stayed there for the next 2 hours. I think it was a sticky thermostat, hopefully not a damaged thermostat. Anyone had a similar experience?
Thanks again,
-David

Sounds like a sticky thermostat...but that is a guess.

As far as American Diesel being all things Lehman....they do not necessarily know what gauge package and do senders are installed.

My rebuilt block must have some unusual oil pressure sender in it as my oil pressure has been 90 psi dropping g to 80 at temp. How would they know what is right or wrong other than matching a correct t sender for a particular gauge?

No matter where you get a gauge or sender...you have to match them....

Really don't think that is the actual pressure....but have t gotten around to fixing every dang problem on the boat and the oil flow has done 2900 hours so it is low on the priority list.

petdoc4u said:

Thank you for all your input.
Given that the engine did not seem to be overheating but suffering from a bad gauge, wiring or sender, I decided to take a cruise. Initially the gauge crept past 200 degrees only to rapidly fall to 180, this seemed to be an intermittent cycle the first 45 minutes. Over time the gauge settled in just shy of 190 and stayed there for the next 2 hours. I think it was a sticky thermostat, hopefully not a damaged thermostat. Anyone had a similar experience?
Thanks again,
-David

Click to expand...

Yes. When I first purchased my new to me trawler with twin 135's the stb engine did exactly what yours is doing. A new thermostat completely cured it.

Ken

Consensus is a bad thermostat. Sender would have been easier to change out but next step will be a new thermostat.
Thank you to everyone for your input. Have a wonderful summer.
-David

Problem Resolved erratic temps

Changing the thermostat, changing the temp sender did not resolve the temp erratic temp problem.
Eventually I decided to disassemble the cooling system to attempt to chase down this problem. I started by removing the hose from the strainer to the raw water pump. Inspection revealed a delamination in the hose at the end closest to the strainer. The delanination was evidenced by a pocket which would form where the inner rubber lining of the hose would separate from its underlayment resulting in the pocket filling with seawater thus blocking flow and causing temp to rise. The pocket would subsequently collapse and water flow and temp would normalize. Replacement of the hose resolved the erratic temps. I suspect that when the hose was originally installed that no or insufficient lube was used and the inner lining of the hose was damaged on the barb of the hose fitting. Boats never cease to present us with perplexing problems. Thanks to everyone for your feedback.

Good find.

Wxx3 said:

I don't think it's the sender, but more likely voltage fluctuation due to changing loads.
But that's my boat.

Since I know the gauge runs between 172 and 188, while the actual temp stays steady at 156 at the top of the coolant tank, I don't worry unless it goes outside that range.

Click to expand...

A 3 wire gauge does not fluctuate with voltage change. They are magnetic field gauges and voltage change on both sides coiis keeping the needle at the same place.