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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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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!

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

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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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Not familiar with the volvo's but just how would back pressure from blocked exhaust elbow

over pressurize coolant system and overflow the ballast tank without a blown head gasket or

cracked manifold? (normal running temp)


What I have experienced if you don't burp the system on a coolant change and leave air in the block

it can progressive lead to dumping coolant/ overheating if you don't top up.

When you start up as air expands in block it can dump coolant when not even hot.

Along with faulty cap. 


I have done several 1KZ-TE heads mainly from overheating, one that went for no apparent reason. (head cracked)

I think gen3's are better with redesigned head, also live longer if you clean the inlet manifold and block the EGR. (amongst other things)


My approach chk would be:



Coolant burp.

Start & run to Operating temp.

CO/bubble check

All negative then,

W/Pump, Raw w/impellor, exhaust elbow, manifold,heat exchanger.

Ah, pretty much what others have said.

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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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