MD11C - WORTH CHANGING THERMOSTAT?

[alisdair4]

I post as a Diesel Engine newbie - although helped by, among other experts OldVic. I am going through the start of season procedure with Midnight Drifter, and have flushed out the antifreeze, run the cooling system through with Fernox (I had suspected it of being scaled up) and tomorrow will change the impeller, oil, oil and fuel filters. The exam question is: is it worth changing the thermostat. (Cost is not an issue, because I inherited a lot of spares when I bought the boat).

The existing thermostat appears to be working OK (ie, I ran the engine yesterday for 90 minutes, and the temperature guage appeared to behave itself). Or should I leave it alone on the grounds of "if it ain't broke, don't (try) to fix it."

Alisdair

 

[VicS]

Right If it aint broke dont fix it.
But if you suspect it take it out and test it . It should just begin to open at the specified temp, 74C I think but check with the manual.
Be warned what appears to be a connection on the housing below the thermostat does not connect to anything, so dont try unblocking a hole that is not there. It'll need a new O ring though to seal it!

 

[alisdair4]

Vic, gut feeling is to leave it alone - I have a to-do list as long as my arm, and unehlpful weather..! Thanks!

 

[FAITIRA]

Remind me Vic, as a matter of interest.
I had an MD11C in a Rival, I think I recall taking the diaphram/valve out, (not the whole thermostat), for some reason, and leaving it out. Why did I do that??? Bill.

 

[VicS]

[ QUOTE ]
I think I recall taking the diaphram/valve out, (not the whole thermostat), for some reason, and leaving it out

[/ QUOTE ] Sorry i dont know what you mean. The WS manual is on the old computer, I'll fire that up later and see if it gives me any clues.

 

[Johnjo]

Probably because removing the thermostat on the MD 11 would allow the cooling water to bypass the actual engine, only cooling the manifold.

 

[FAITIRA]

[ QUOTE ]
[ QUOTE ]
I think I recall taking the diaphram/valve out, (not the whole thermostat), for some reason, and leaving it out

[/ QUOTE ] Sorry i dont know what you mean. The WS manual is on the old computer, I'll fire that up later and see if it gives me any clues.

[/ QUOTE ]

Don't go to a lot of bother Vic, I took out the disc in the middle that does the closing, not the whole thing, it never went back, but I can't for the life of me remember why I did it. Bill.

 

[FAITIRA]

Don't know Mike, but we spent a year going to the Med and back after that. Bill.

 

[VicS]

[ QUOTE ]
I took out the disc in the middle that does the closing

[/ QUOTE ] Thereby making the thermostat open all the time. It would have made the engine run cold. therefore less efficient and cause water vapour to condense and the oil to be wet. Not advisable.
Not absolutely sure why you did not simply remove the thermostat but perhaps because its is necessary to support the seal for the cover. IIRC it fits onto the flange of the thermostat and would collapse on its own.

 

[Saddletramp]

I removed the stat to see why I was getting poor circulation and you are right you can not get a seal because of the flange.

 

[FAITIRA]

[ QUOTE ]
[ QUOTE ]
I took out the disc in the middle that does the closing

[/ QUOTE ] Thereby making the thermostat open all the time. It would have made the engine run cold. therefore less efficient and cause water vapour to condense and the oil to be wet. Not advisable.
Not absolutely sure why you did not simply remove the thermostat but perhaps because its is necessary to support the seal for the cover. IIRC it fits onto the flange of the thermostat and would collapse on its own.

[/ QUOTE ]

All you say, as usual, makes sense Vic, I am going to have sleepless nights now trying to defeat the 'memory loss', it made sense at the time but i'm bu##ered if I can remember why. Bill.

 

[Saddletramp]

All you say, as usual, makes sense Vic, I am going to have sleepless nights now trying to defeat the 'memory loss', it made sense at the time but i'm bu##ered if I can remember why. Bill.

[/ QUOTE ]

Don't you just hate it when he does that /forums/images/graemlins/wink.gif

 

[Johnjo]

[ QUOTE ]
Don't know Mike, but we spent a year going to the Med and back after that. Bill.

[/ QUOTE ]

What i was trying to explain was that the thermostat on the md 2 isnt your run of the mill stat, when the engine first starts or until it reaches its running temp 60c if i remember correctly, its a low temp stat because its salt water cooled, anyway until the engine reaches operating temp the cooling water passes through the manifold, as the engine heats up the stat obviously opens allowing coolant to circulate around the engine, in doing so it closes off the bypass port in the manifold, water will still enter the manifold but its gone through the engine first, hope this helps

 

[VicS]

[ QUOTE ]
What i was trying to explain was that the thermostat on the md 2 isnt your run of the mill stat

[/ QUOTE ] The original question was about the MD11. When cold the water flow bypasses the engine and manifold, flowing via a bypass port in the thermostat cover directly to the exhaust injection point. (there may be a very small flow through the engine via a small hole in the thermostat as well) When the engine warms up the thermostat opens and allows a flow via small passages in the manifold to the heads and then via other passages in the manifold to the thermostat after which it joins the flow through the bypass in the cover.

You now talk about the MD2 but as far as I can determine the cooling water flow is the same.

I have no recollection of a bypass port in the manifold or any mechanism by which the thermostat controls it.

You are right about one thing. The thermostat starts to open at 60C not 74C as I said earlier. It should be fully open at 74C

 

[Johnjo]

sorry i was under the impression the md 2 an the md 11 was the same engine, there isnt any mechanism its just a bypass port.

anyway will consider myself better advised

 

[FAITIRA]

That was the anomaly I was on about, the thermostat works 'back to front', thats the reason I only took the 'middle' out, I remember the wee bleed hole now. But why, did I take the 'bleeding middle out??? Bill.