Volvo MD7A Back flushing

[aquaholic]

Have noticed that the engine doesnt seem to throw out much water when running even though I have changed the impellor and fitted a new exhaust elbow this year, I have heard that back flushing may help improve water flow, if so what would be the best way to do this? i.e where do i stick the hose.........if you catch my drift
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[gandy]

Does the engine run too hot, or hot at all? If not I'd be inclined to leave it. Last winter I replaced the thermostat on our MD7A, and it turned into a real pig of a job.

 

[Kylora]

I'm not convinced that back flushing would improve your situation.

My experience is with the MD6A which might vary slightly from yours.

In simple terms, the usual flow is from the raw water pump into the engine and out of the engine to the elbow.

Reverse flushing would involve connecting the mains hose to the pipe which normally connects to the exhaust elbow and removing the hose from the pump outlet and arranging for the water to run overboard.

The thermostat will be shut so has to be removed to allow flow ( and the housing refitted ). The flow will then bypass the engine through the hose from the thermostat housing running under the manifold to the tee piece - this hose needs to be clamped closed.

I've used brick cleaner ( the acid based one - the alkali one doesn't work ) to clean the gunge out of the waterways of the 6A - this was to improve overheating and warrants a separate reply.

I would have expected reduced flow to be either a restriction on the inlet to the pump or wear in the pump - back face / cover face / cam.

Ash

 

[thalassa]

Most MD7A raw water pumps are rather small, so pump out relatively little water. Also, they are very susceptible to losing power due to scouring of the pump insides. Start with reversing the bronze pump cover, or have the inner side flattened.
Best wishes.

 

[Bilgediver]

If the MD7A is similar to other volvo engines of that era then the cooling water takes two paths under the manifold. One path is through the engine and to the thermostat and the other path by passes the engine direct to a restrictor nozzle on the bottom of the thermastat outlet side and provides water to the exhaust when the thermostat is closed. It is not unusual for this nozzle to get blocked by bits of impeller.

Check this is clear.

 

[Mudhook]

My MD7 water output is tickover (911 rpm): 1.8l/min; medium speed (1540 rpm): 2.4l/min. I would file that as "not a lot". However the temperature is always on the low side of the gauge and I don't experience any cooling problems. Despite long conversations on the MD7 with various old Volvo experts, no-one has ever suggested back flushing. In fact I've never heard of it before. Plus, water in error up the manifold and into the cylinders will **** your engine.

 

[aquaholic]

Maybe I will just accept that it doesnt throw out gallons of water and wait until there's a problem. Thanks again.

 

[saltwater_gypsy]

AH !!HA!!!!
No one has mentioned the gearbox.
On the MD7A the water circulation also goes to the gearbox and this is a popular spot for blockage as it is the lowest point in the cooling system and silt tends to collect there. So, get a wire coat hanger(which every PBO forumite carries) and undo the two unions on the gearbox. Poke around and flush and poke around again and flush.
I hope this helps.