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Old 23-08-2014, 15:18   #1
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Underheat Problem. MD7A

I had then engine out of the boat for all winter, sitting under a tarp, winterized while I did a lot of work in the engine compartment. I put her back in and she starts up just like always.

But she won't come up to temp.

I replaced the thermostat, the housing was pretty cruded up so I took care of that. I have a brand new control panel with new sender. But that seems to work just fine. New sender has same resistance as old sender and came with the panel so matches the Faria gauge.

I can easily hold my hand on the water manifold. Using a IR thermometer the highest reading I got was 125, after the engine was shut down for a few minutes. That is about what the gauge reads. But while running she shows about 110.

Any suggestions?
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Old 23-08-2014, 15:31   #2
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Re: Underheat Problem. MD7A

Thermostat stuck open.
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Old 23-08-2014, 15:37   #3
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Re: Underheat Problem. MD7A

Quote:
Originally Posted by hpeer View Post
I had then engine out of the boat for all winter, sitting under a tarp, winterized while I did a lot of work in the engine compartment. I put her back in and she starts up just like always.

But she won't come up to temp.

I replaced the thermostat, the housing was pretty cruded up so I took care of that. I have a brand new control panel with new sender. But that seems to work just fine. New sender has same resistance as old sender and came with the panel so matches the Faria gauge.

I can easily hold my hand on the water manifold. Using a IR thermometer the highest reading I got was 125, after the engine was shut down for a few minutes. That is about what the gauge reads. But while running she shows about 110.
Any suggestions?
!ST HAVE YOU SHOT YOUR ENGINE WITH A DIGITAL LAZER POWERED THERMOMETER YOU COULD FIND YOUR SENER OR GUAGE ARE OUT ALSO IF YOU ARE OPERATING IN SALT WATER 110 IS NOT A BAD TEMP AS IT WILL NOT ALLOW SALT TO CHRISTILLISE AND STICK TO THE WATER GALLERYS INSDE YOUR ENGINE BLOCK MOST ENGINES RUN AT 110 YOUR OLD THERMOSTAT MAY NOT HAVE BEEN OPENING FULLY DONT THINK YOU HAVE A CONSERN
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Old 23-08-2014, 17:32   #4
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Re: Underheat Problem. MD7A

The first thing I did was to replace the thermostat. So this one is brand new.

Well she IS a raw water cooled engine. If I recall correctly the old gauge showed her running at 180. Of course my memory is always suspect.

Don't know how to confirm the factory spec on cooling for this engine.
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Old 23-08-2014, 17:42   #5
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Re: Underheat Problem. MD7A

180 degrees is too hot for a salt water cooled engine. 160 degrees is max and well below that is better to give you a cushion of safety. Above 160 degrees, saltwater begins to leave serious deposits in the engine possibly blocking water passages. My old MD2B Volvo never got hot enough to make warm water in the water heater. 110 degree may be a bit low but better low than too hot. Pull the thermostat and put it in a pot of water and heat. Note at what temp it opens and that should be the temp the engine runs at. If temp is significantly different from the advertised operating temp. of the thermostat, you have a bad thermostat.
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Old 23-08-2014, 18:00   #6
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Re: Underheat Problem. MD7A

Most those RWC Volvos run real cold as I remember. definitely shouldn't be 180. maybe it used to run too hot due to the buildup of junk...?
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Old 23-08-2014, 18:03   #7
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Re: Underheat Problem. MD7A

cheeko, you may be onto something.

I just ran through the engine manual and that says the stat should start opening at 140 and be fully open at 165.

Still 110 sounds damn chilly.
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Old 23-08-2014, 21:44   #8
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Re: Underheat Problem. MD7A

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cheeko, you may be onto something.

I just ran through the engine manual and that says the stat should start opening at 140 and be fully open at 165.

Still 110 sounds damn chilly.
For raw water cooled engine the engine temperature should never rise about 130 degrees F. Higher temperatures would cause the minerals to separate from the water and clog the water jacket in short order.

The 140-165 would be correct for fresh water cooled engine, but never for a raw water cooled engine. 110 is cool, but far better then 160. Lordy that's too hot.
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Old 24-08-2014, 06:22   #9
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Re: Underheat Problem. MD7A

Ok and thanks all. I'll try to 'chill' and relax about the temperature.

I appreciate all the advice.
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Old 24-08-2014, 09:14   #10
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Re: Underheat Problem. MD7A

I was so surprised about the 165 degree running temp, that I checked my manual and yup, thats what it says. Does anyone out in CF land have a manual for any other brand of raw water cooled engine to compare what they recommend? The chemistry of salt participating out versus temp is the same no matter what brand name is on the motor. hpeer, something else just came to my (feeble) mind. When you reinstalled your engine, you may have cleaned up a wire connection for the temp gauge, and now be getting the real reading as opposed to a dirty (high resistance) connection. I remember an earlier post of yours where you mentioned 180 degree running, and I thought that something was badly wrong. It may be running at the same temp as before, but with the gauge reading correctly now. I still have doubts about 165 being correct for a raw water cooled engine. Best of luck._______Grant.
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Old 24-08-2014, 09:37   #11
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Re: Underheat Problem. MD7A

Grant

I found this.

Can Your Cooling System Take the Heat? | Cruising World

Quote:
A more insidious drawback to the raw-water system is that the engine must run cooler than it could with a closed system. Above 160 F, sea salt begins to crystallize inside the cooling-system passages. This not only accelerates corrosion but also, in extreme cases, can actually block passages. For this reason, most raw-water-cooled diesels have a thermostat set at 145 F, at least 40 F cooler than a closed system. Running at this relatively lower temperature reduces an engine’s thermal efficiency, so a raw-water system simply is unable to produce as much usable power as its closed system counterparts.
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Old 24-08-2014, 10:46   #12
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Re: Underheat Problem. MD7A

My old MD1 ran very cool. dont remember the readings, but you could hold your hand to it without getting burned. I have not yet run my MD7A, but it is fresh water cooled, so when I get around to running it, the first thing I will check is the thermostat. No sense having fresh water cooling, if you are going to run at raw water temps (other than corrosion). The only thing I dont like about the fresh water cooling, is that it eliminates the hand crank ability. If a starter motor packed up, I think it would only take an hour or so to change back to raw water which would free up the crank position. I will carry both thermostats, just in case. A note!! on this forum (several months ago) I read a post that said you can not run a RWC Volvo without the thermostat in place, because the flow of water would be allowed to go directly through the exhaust without going through the engine cooling passages. I dont know if that is true or not, but I made a note in my manual just in case. Got to love the old GREEN DEMONS. ______Grant.
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Old 24-08-2014, 11:20   #13
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Re: Underheat Problem. MD7A

I know how to make you jealous!

I just bought a SPARE MD7A. I have no idea of the condition yet, but it looks complete.
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Old 24-08-2014, 19:27   #14
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Re: Underheat Problem. MD7A

I am prepared for jealousy competition!!!! When I bought my MD7A it came with a spare head, valves, injectors, starter, alternator, raw water pump, and a lot of new replacement parts. I.E. several impellors, and several seals (not sure for what) and a bunch of other stuff. Oh yes, also an extra injection pump with 10 hours since overhaul. It also came with low compression (ring job ahead) which I will check the cam timing before I do the rings. Oh yes, the head had been rebuilt (and injectors) only a few hours before. Since it didnt come with a transmission, I bought an MD6B to get a tranny and it came with another starter and alternator, and water pump, but many of the other parts are not compatible. I think the exhaust manifold might be the same. OMG I feel like a rooster crowing on a fence. I almost bought that MD7A that you have when you hesitated a week or so. I would have paid that price just for an extra tranny. Best of luck with your cooling problem. ______Grant.
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Old 24-08-2014, 19:53   #15
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Re: Underheat Problem. MD7A

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Originally Posted by gjordan View Post
I am prepared for jealousy competition!!!! When I bought my MD7A it came with a spare head, valves, injectors, starter, alternator, raw water pump, and a lot of new replacement parts. I.E. several impellors, and several seals (not sure for what) and a bunch of other stuff. Oh yes, also an extra injection pump with 10 hours since overhaul. It also came with low compression (ring job ahead) which I will check the cam timing before I do the rings. Oh yes, the head had been rebuilt (and injectors) only a few hours before. Since it didnt come with a transmission, I bought an MD6B to get a tranny and it came with another starter and alternator, and water pump, but many of the other parts are not compatible. I think the exhaust manifold might be the same. OMG I feel like a rooster crowing on a fence. I almost bought that MD7A that you have when you hesitated a week or so. I would have paid that price just for an extra tranny. Best of luck with your cooling problem. ______Grant.
Bugger, you win!
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