MD11c underheating

[Geoff K]

Well, I don't know if there is such a word as "under heating" but my MD11c will not budge the temp needle. New gauges were installed 3 years ago and the engine has run cool ever since, usually 120-130 range. (It was not my boat prior so I don't know what it did before.) However at that temp the reading is not clear; not sure what the running temp really is but it's less than 170. The mechanic who put the gauges in said he had checked the thermostat and didn't know why it was running cool.

This year the needle doesn't budge. I assumed the gauge was not working until I forgot to open the cooling inlet seacock. When the exhaust sound changed (no water in the muffler) I realized the problem. The temp was 160. Bu the time first mate got below and opened the seacock it was 180. Then it came back to the 120-130 range. Engine seems to run fine. It hasn't been run since.

I'm guessing the thermostat has been defective with partial opening (leaking?) all along and this year it just stuck open. Before I dig into the bowels of the engine compartment (or pay big bucks to have someone else do it) are there any other ideas I should pursue?

The boat is in, and has been for 20 years, fresh water.

Geoff

 

[kloudie1]

Does the engine have a heat exchanger or is it sea water cooled? If seawater cooled, the thermostat could be a cool one at less than 140 F (prevents salt deposits in the block and head). Ya have to choose the gauge carefully to get a usable reading at the cooler temperature .. Since you are in fresh water and not salt, you may be able to go up to a 160F thermostat ..

 

[Bill Roosa]

Just about the only thing that can make it underheat is super cool raw water or a stuck open thermostat.

 

[Geoff K]

It's seawater cooled. Lake Superior's average temp is in the upper 40s to lower 50s though it is warmer in the marina and in shallow bays. I'd like to go to a warmer thermostat. Are there and caveats? Any reason I might not want to?

Geoff

 

[kloudie1]

My point then is that the gauge may be a little off and the raw water thermostat is the correct one for salt water.. and it is doing its job .. but the gauge just doesn't read accurately at the low end..
A warmer thermostat .. like 160F (70 or 71 C) in fresh water would be fine; the only caveat would be to retain the old one in the event that the boat goes to salt water at some point. A gauge like this http://www.egauges.com/vdo_ind.asp?Type=Elec_Engine_Temp&Series=EVA&PN=R5150
that has an expanded low temperature range would be easier to read with the old thermostat.. and would be fine with a warmer one too..
Good Luck with it Geoff

 

[Geoff K]

Claude, that makes a lot of sense. I like the gauge you've led me to. My winter project... replace the thermostat and replace the existing temp gauge.

Thanks

Geoff

 

[Mark Maulden]

Why don't you get a cheap IR meter and read directly off the engine at different points

 

[Geoff K]

Interesting thought. But how do I know how to interpret the temp readings off the engine? Is there a standard temp for specific areas that applies to all engines?

 

[Mark Maulden]

You know what your T-stat is. You can shoot that area. The exhaust manifold will probably be a little warmer. The cylinders will also be a little warmer. The whole idea is to check the gauge. If the gauge is still on the cool peg, and the engine is "at temp" then you can fault the gauge or the sensor or the wiring.