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Volvo MD2030 dumping coolant

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I thought I'd try the collective wisdom here before i start down the rabbit hole of diesel engine trouble-shooting.


Over the weekend and while on the marina berth I started the above engine, and after a short period in idle, i upped the revs (in load) and headed down below. Only to discover the overflow pipe beside the filler cap was dumping green (antifreeze) water in the bilge at a rabid rate, and hence i shut it down!  

After a minute or two, i opened the filler cap (small amount of pressure) and, expecting the exchanger tank water to be empty or hot, stuck my finger in to discover it was full and lukewarm. Hence i need to figure out whats going on?!


Interestingly, while the engine was running, the raw water flow out the exhaust went from a good heavy flow to a much lighter flow and hence why i checked the engine.


My thoughts are it could be as simple as a knackered filler cap that's popping open due to the water-pump pressure, but that wouldnt happen (much) if water was circulating through the engine properly, hence i suspect a blockage somewhere or possibly a dodgy thermostat, if it has one.


Sooo, are there any obvious trouble shooting, or simple fixes i should try before I call the mechanic?


Any tips welcomely received



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Pretty Much just start methodically checking and eliminating all components. 


Fresh Water Pump impellor

Thermostat (it will have one)

Heat exchanger core and end caps

Exhaust elbow

Any Rubber hoses carrying coolant.


Should not be the raw water pump as far as I can figure


For our overheating problems it turned out to be a clogged exhaust elbow, last thing we checked after weeks of work, sods law.

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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 thing to try is to replace the cap, or pressure test it. IIRC those were only about 7psi before venting...


If you take off the cap, and you can see oil, diesel or bubbles in the coolant, (while the engine is running) you have a serious issue.

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You are spot on by starting off simple and working up toward the hardest.
The cap may not be sealing. As the engine warms up, the pressure increases due to expansion.
You may also have a blockage in the Heat exchanger and or exhaust mixer. That is unlikely to cause a problem immediately, but only after the engine is hot and working.
There maybe an exhaust leak in the exhanger Although that normally causes coolant drain once the engine s shut down and allowed to cool
Check the Termostat is opening and doing so at correct temp.
The impellor may have lost a blade or more.
There is a test that can be done to check for Co in the water. Pop into a Workshop and ask if you could buy a test strip off them. That very quickly tells you if you have a gasket issue.
All the above is what normally takes place, But the norm does not always take place, especially when some one states that the various points are the norm.

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Many thanks everyone for the input - much appreciated!


It sound like a methodical approach starting at the cap, impeller, then check and clean the heat exchanger, check thermostat and then exhaust mixer will be the plan - fingers crossed. 


As an FYI, the engine was rebuilt less than 100 hours ago but has had very little over the past few years hence I'm pretty comfortable its not a head gasket, also, the water in the heat exchanger is perfectly clean, but we will see. . . . 


Lets hope i havent killed the engine for the second time  :roll:


Thanks again, I'll report back once i find some time to get into it

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"Interestingly, while the engine was running, the raw water flow out the exhaust went from a good heavy flow to a much lighter flow and hence why i checked the engine."


Water must have backed up into your exhaust and into the piston chamber. Water wont compress. I would put money on the new head gasket.


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Seems to me it’s getting water from somewhere else meaning a breach in raw water/fresh barrier.


Thats exactly what some others are suggesting on another forum as someone else had the same issue. A breach somewhere in the raw water/fresh/exhaust system is causing back pressure when the revs increase.


First plan of attack will be to checkout the heat exchanger and raw-water exhaust mixer and their connections

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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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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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While on the subject of "Pressure" does anyone have a diesel compression tester I could borrow ? I have a sick Volvo MD7B and I want to check the compression before pulling the head off. 


I'm in Howick



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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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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)



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1 hour ago, vic008 said:

Had great success with putting a bung in one end and filling with hydrochloric acid for 6hr

Yeah, ive heard that as well - unfortunately i don't have any and the white vinegar alternative isn't doing much.

I really dont want to take a trip to Bunnings hence I'll try poking it clean with some wire and see how it goes.

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