Ford Lehman Operating Temperature

[diversion]

I have a question.

Is the header tank temperature the same as the engine temperature after the engine has reached operating temperature? Underway, my gauges read 185 degrees but an infrared heat gun on the header tank reads 175 degrees and no hotter on the block near the temp sending unit. I recently installed a new thermostat and vent tube and am getting different readings than in the past.

Anyone have any experience with this?

I have owned the boat since new for 21 years. Its in great shape and the engine runs great.

Any help would be appreciated.

[Mariner]

I would expect that the exterior of the engine would read a little bit cooler than the interior. Even after it has been running for a long time, the metal acts as an insulator, and the bulk of the heat is expelled through the coolant out of the exhaust. That would explain why the readings you're getting on the exterior of the engine would be a little cooler than the coolant temperature gauge. Do you have an oil temp gauge?

[diversion]

You're probably right about the difference in temp but I wonder if it is a 2 degree variation or something more like a 10 degree variation.

I don't have an oil temp gauge but I will look into it.

Thanks.

[Merry Kate]

Diversion -

Shooting your header tank will give you an accurate reading on your coolant temperature once up to temp. Shoot the thermostat housing to verify. Then, you've just calibrated your engine guage (sounds like it's reading 10 deg high - not at all unusual).

There are all kinds of temperatures on different parts of your engine. An IR gun is one of the best diagnostic tools to have on a boat. If you're into that kind of thing, it's fun to see temps on the various parts (e.g. the exhaust manifold near the head will be 100's of degs). A very useful application is to shoot the inlet end of your heat exchanger and the outlet end. A 20-30 deg gradient tells you all is working well.

Running 175 deg on your 21 year old Lehman is awesome. Great motor and great maintenance program you've done!

[diversion]

Thanks for the reply and the great tips. I will check out the other areas you mentioned this weekend.

[jleonard]

According to Bob Smith, the Lehman guru, the proper way to monitor temp is via a manual gage off the header tank.
My Lehman came to me already set up that way and it does run about 180 there although the temp gages on the instrument panel read 185/190.
I also verify all those readings with a temp gun on a regular basis and as you found I get around 178 or so at the header tank and 175 to 185 elsewhere.
Hope this helps.
Happy cruising.

[diversion]

Thanks, I will check into the manual temp gauge.