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Volvo MD2030 dumping coolant

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Think about this.

The pressure in the cooling circuit (about 7psi IIRC for those, up to 15psi or more for some engines) is higher than the raw water cooling circuit.

So, if there is a breech between these two, the coolant is lost into the raw water flow, not the other way.

A complexity is if there is compression leaking into either circuit - it is MUCH higher pressure than either, and will get out however it can.

If it leaks into the coolant, it will blow it out the pressure cap, or rupture a heat exchanger, cooled manifold etc. If its into raw water, it's often not so noticeable as it will go out via the exhaust.  

Sometimes, if compression leaks into raw water, then it can reduce raw water flow, sometimes by a lot. 

Exhaust pressure in a diesel can be a bit as well, and can stop water flow from either system.

So, in the reduced water flow situation, AND loss of water from header tank, the chances are good that compression or exhaust pressure are leaking into the other systems. 

There is no place in the engine where all three (raw water, coolant, exhaust) come together, so it would indicate multiple issues. 

the multiple issues could have one cause - if exhaust leaks into coolant via head gasket, for example, the extra pressure could rupture the heat exchanger. Things like water cooled manifolds can make matters worse.

So, begin with the basics, then move on to the  more complex. If you are taking off heat exchanger, both flow and pressure test - "looks ok" is not OK. Same for water cooled manifold, exhaust elbows,  etc.

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Either the coolant circuit is over pressure (compression or exhaust leak into it, head gasket, failed manifold, failed heat exchanger are all possibilities) or the coolant cap is knackered. Cheapest t

Start with the easy ones, & possibly save some skin. Get wet, as it’s hot, and check there’s no fish up the Rw intake!

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As IT said and i ehoc his comment, Think about it.

The reducing water flow in the exhaust is a red hearing. The volume of water going anywhere else it should not is ludicrously large. Water flow is either normal or that is a separate fault. NOTHING to do with the engine coolant.

The pressure cap is a pressure cap for a reason. As the engine/coolant warms, the coolant expands and has to go somewhere. The pressure increase aids in allowing a much higher boiling temperature. With no cap, the water will spew out the top as it warms up. If the seal is damaged, then the water will spew out and into the filler bottle (if you have one)

If you have a blown head gasket, there will be other tell tale issues. Blown between a cylinder and cooling jacket results in coolant being sucked back into the cylinder as the engine cools down after shut down. At restart, the engine will be hard to start and will run ruff till the water is blown out and the the exhaust will be smoking badly. That's at best.

Very simply, buy a new cap. Check the seat is clean. Do not warm the engine up with cap off. Check coolant levels when engine is cold.

As a separate issue, check the raw water pump impeller. If the impeller has seen a few seasons, replace it anyway. Check the filter basket is clean and if the impeller had failed, check no bits of blade are stuck in the pipes.

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Many thanks all for the additional input - its going to be interesting to figure this one out!


Touching on your comment IT "AND loss of water from header tank" whilst its loosing water from the header tank, the level doesn't seem to decrease?!?!, hence im thinking raw water is getting into the coolant as pressure builds with the revs . . .  maybe


Anyway, I'll start with a new cap, check impeller, then disassemble, clean, inspect and reassemble the the header tanks and exchanger to the exhaust mixer and see what reveals itself, if anything. Ah the joys. 

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hence im thinking raw water is getting into the coolant as pressure builds with the revs . . .  maybe


Highly unlikely. Raw water pump would not be reaching enough pressure to overcome the Coolant pressure. Raw water is pretty much no pressure. Exhaust pressure is only around 1 to maybe 3PSI absolute max and at which there would be other problems. So the Raw water does not have to overcome much to empty into the exhaust.


If you leave the engine running, does the coolant eventually stop running out??


I just went back and re read your first post. I suspect the header tank is too full.

Either there is a level you are not supposed to fill over, or you need a small drain tank to take excess coolant during expansion as the engine heats up, which then sucks back into the tank as engine cools. I suspect the engine has always spat out excess coolant in the past and you never knew.

However, if you do fit a catch can of some sort and the engine keeps "making" coolant, at least you will know for sure it is more than simple heat expansion.

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  • 2 weeks later...

A compression tester may not tell you much with a diesel. The compressions is so high that you can get acceptabel results even when there is a serious problem. For Diesels, the normal test is with a device called a leakdown tester. However, you need a constant air supply to be able to do this. The tester measures the differential of pressure against how much air leaks past the tester. This test is also great at being able to locate where the air is leaking past, by listening for leaks. i.e, perhaps a leaking valve seat for instance, or if the air is leaking past the rings and so on.

Chris, what is the suspected problem. Maybe we can advise you if the head should come off based on the symptoms, rather than a test.

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  • 2 weeks later...

Has there been any development on this story yet? Any fault found?


No not yet. Life keeps getting in the way.


Im hoping to pop down this weekend and at least start the engine for a few minutes and take a further look.


The wife and daughter are heading overseas next school hols so I'll attack it in anger then

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Quick update on this since a few of you are interested.

I finally got down to the boat last weekend and after tearing apart the raw water cooling system, i discovered a VERY blocked up water injection mixer (see pic) that Im 99% sure is the problem. The raw water intake side of the mixer (not exhaust) is completely gunked up and will be cleaned out this week and re installed.

Volvo Exhaust 2010 2020 2030 2040 D1 D2 Exhaust water injection ...

I suspect the raw water was under such pressure due to the blockage it was forcing its way back through the rubber connector (and clamp) that seals the heat exchanger, and into the fresh water system. (not actual photos BTW)



Edited by tuffyluffy
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