Engine running too cool

[JMS02050]

Never thought I'd be writing about this...

MD7A was running hot. Replaced impeller and got great exhaust water flow, but now I can't get the temp gauge about 110. Replaced thermostat. Still reading 110. Tested gauge (passed) and use infrared temp gun on engine and exhaust water... all reading about 100-110.

What could be causing this? Any help is appreciated.

-Jim

[Rockter]

Is it a raw water cooled motor, like my olde MD17C ??

[JMS02050]

Engine is a 1981 raw water cooled MD7A.

[Rockter]

That does seem a bit cool.... 43 degC.

I wonder is the new thermostat working fine?

Does the temperature oscillate on the guage a wee bit, say over a minute or so?

Overcooling is a bit rare.... normally the thermostat is stuck open. I can't see another reason for it. Does it still hover at 43 degC under sustsined load?

[JMS02050]

She doesn't budge, regardless of load or duration. I've run her hard for a couple of hours. Readings, both temp gauge and exhaust flow via temp gun are the same.

[Rockter]

I would suspect the thermostat. The temperature really should oscillate visibly on the temp guage, perhaps moving every 20 seconds, or so, under load.
I would take it out and test it. Boil it in water. It must be seen to open.

[JMS02050]

Tested the new tstat in a pot of water. It's working properly so I'm completely stumped.

[Rockter]

What did it open at there JM? Is it the right thermostat? Were your observations made under load? Put it in gear and work the motor a while.

If the thermostst is shut, the temperature in the water jacket really should rise until the thermostat opens, then the temperature guage will drop abruptly.... then it repeats. There really is a lot of heat thrown off by the liners and cylinder head, enough to boil the jacket water promptly if the thermostat is closed.

I am puzzled.

Put your hand onto the top of the exhaust manifold where the water is injected into it. Does the temperature oscillate (after warm up and under load) ? Take the wee temperature sensor plug out, touch the body of the plug to the manifold (to keep electrical continuity) and pour some boiling water over the temperature sensor. Have a friend tell you if the temp reading is changing.

[JMS02050]

Using OEM tstat from Volvo rated for 140-160 (fully open). I pulled and tested the thermostat and it works perfectly. I'll try the tests that you've recommended. This one baffles me.

Jim