VW diesel marine conversions

Discussion in 'DIY Marinizing' started by moTthediesel, Apr 6, 2006.

  1. Petros
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    Petros Senior Member

    a cooling system is a realatively simple thing, and cooling problems in both boats and cars can sometimes seem impossible to solve. You have to approach it logically: coolant circulates via the pump, the coolant heated by the engine and it is cooled in some short of heat exchanger. Verify everything is working and narrow down possiblities. Do not randomly replace parts without dianosing the problem first, that is a waste of time and money and usually does not fix the problem.

    Even a leaky head gasket or cracked block will stay cool without overheating until you loose enogh coolant to not allow it to cool. That normally takes longer than 5 min. If it get hot that quickly it sounds like it is not cooling at all, that is about how long it takes to heat up. Check you are not sucking any hoses shut on the suction side of the pump, check you radiator cap is good, and your thermostat is good (do not assume that it is good just because it is new, many are junk right out of the box).

    In many systems that were not designed for a boat, you can trap large air bubbles in the system that prevents circulation or proper cooling. You have to bleed the air out before it will cool properly. Sometimes you can do this by removing a fitting or hose from the highest point on the engine and fill it from that point until it is full, and than quickly connect the hose without allowing too much air in the system (many cars have this problem too). Sometimes you can trap large amounts of air in the heat exchanger causing the same problem, if there is no easy way to bleed the air out you might try adding a bleed port (a simple plug or bolt in the correct place). If you are using a seawater to engine coolant heat exchanger you have two places that can trap air, in the seawater side and in the coolant side. You should also verify that seawater is circulating the way it is supposed to as well.

    You might install temporarily some lengths of clear plastic tubing to see if the coolant is circulating. Some inexpensive thermometers attached to the various components (including the inlets and outlets of each component) will tell you if the coolant is being cooled as it runs through the heat exchanger, that will help narrow down the problems. You also might check the capacity of the heat exchanger (rated usually in btu/min or cal/min) to make sure it is large enough for your needs.

    It is just a matter of narrowing down all the possible problems. It is usually not some exotic problem (like the wrong impeller on the water pump), but will become obvious once you do systematic testing of the system and narrow it down. You have already spent a lot of money NOT solving the problem, so instead of throwing parts at it, now take the time to find the problem and fix it once.

    Good luck.
     
  2. CDK
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    CDK retired engineer

  3. baeckmo
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    baeckmo Hydrodynamics

    Ashley, the one thing you did not mention was thermostat. Has it been changed/checked? Can you describe the cooling system more "systematically"?
     
  4. jonr
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    jonr Senior Member

    If you are getting sufficient coolant flow, then I'd look for a clogged passage or an air bubble. You might have low flow and steam forming in one area while other areas are working fine. You might even use an IR thermometer to check that the heat pattern on the block is symmetrical.
     
  5. AShley5031
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    AShley5031 Junior Member

    Vw marine diesel

    Thank you for your very helpful reply. I have taken out the thermostatic valve to see if the engine runs cooler......could this cause any problems?
     
  6. AShley5031
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    AShley5031 Junior Member

    VW Diesel marinization

    Thanks Baeckmo, yes I have changed the thermostat....three times! Today I took it out, to see if the engine runs cooler...do you foresee any problems other than taking longer to reach operating temperature, which would be a nice problem to have!
     
  7. AShley5031
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    AShley5031 Junior Member

    VW marinized diesel

    Thanks Jonr,

    I have not found any restricted passages in the cooling hoses, and I checked them again today. I have tried to get rid of air bubblesby squeezing the hoses, I thought I had got rid of them..but you never know. A friend told me today that his VW 1.6 gasoline powered car always chucks water out of the expansion tank until it is halfway down. So I will be filling up to halfway tomorrow to see if it chucks out any more. I have also fitted a pressure gauge to the fresh water system which stays steady at 1 bar.
     
  8. baeckmo
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    baeckmo Hydrodynamics

    Taking away the thermostat will normally cause overheating, since modern thermostats have a shunting function. When the engine is cold, water is recirculated directly from the engine into the circulation pump inlet, connection to the cooler is closed. With increasing engine temperature, the shortcut into the pump is closed and the flow is directed through the outer cirquit where it passes the cooler.

    Now, if the thermostat housing is empty, all the water will take the easiest way around, i.e. directly through the shortcut, and nothing passing the cooler. The result: overheating engine!! So never run an engine without a thermostat!!

    BUT: if you change thermostat, beware that the "shunting valve" has the correct configuration, since if wrong it may leave the shortcut open when it should close.

    The failure sequence often the following: First the original thermostat gets tired and the engine tend to run hot. Second a new one is installed, "thermo is a thermo, same same but different, it fits the housing flange and has the right temperature setting...". Third the iron still overheats, owner goes bananas as more and ever more parts are swapped in vain........!
     
  9. AShley5031
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    AShley5031 Junior Member

    VW 1.6 Retipar marinized diesel

    Hi Baekmo,

    Reading your message again...here is a better description of the cooling system.

    There are two basic circuits, one fresh water and one salt water. If the thermostatic valve is fitted, the following happens: The valve cold remains closed and the fresh water circulates through the block and head driven by the fresh water pump in a short cooling circuit, which does not include the heat exchanger. When the valve opens, supposedly at 80 degrees C, it forces the water through the longer circuit, which includes the heat exchanger. The fresh water passes around the outside of the heat exchanger tubes, while the salt water passes through the middle. The salt water cooling circuit is driven by a Jabsco pump with a rubber rotor. The water is sucked through an intake (1/2 inch) in the hull, passes through a filter, then goes to the pump, thence to the heat exchanger, then returns via the exhaust into the sea, the hot seawater mixing with the exhaust smoke. The outlet is actually slightly under water, which makes flow observation difficult, but the filter has a transparent top, through which one can see the water moving. If it is full, then the water is circulating OK. If not full, it means that there is a barnacle build-up on the intake.

    What is happening is that once the engine has warmed up, it starts to chuch water out of the top of the expansion tank, and the engine heats up to 100 degrees and the siren goes off, when of course I switch it off. The cap is new and opens and closes correctly, keeping the pressure at 1 bar. The heatexchanger/manifold assembly showed no signs of water contamination on the exhaust side when I took it off, so I have assumed that there is no leak between the exhaust and the fresh water system. If the gas coming out of the expansion tank was combustion gas, surely it would be black and smell of smoke? It would also start immediately when the engine starts…but it doesn’t. The gas bubbles only appear once the engine as warmed up, so maybe this is just steam. But where is the steam coming from? The block has just been tested and reconditioned.

    And there it is……any suggestions would be most gratefully received

    Ashley
     
  10. Petros
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    Petros Senior Member

    with your system it does not sound like running without the thermostat would be a problem, it would just take longer to warm up (it is supposed to keep the engine within a certain temp range, but running it cool would not harm the engine). On modern car installations the t-stat circulates coolant through the heater core until it warms up, and the t-stat redirects the coolant to the radiator. Removing it causes coolant not to circulate properly since it will flow into all hoses, rather than where directed by the t-stat.

    It sounds like there is a large air bubble trapped in the cooling system somewhere. I had an old Diesel Mercedes Benz that would trap air in the back of the head when filling it from empty. It would over heat even if everything was operating normal. I had to bleed the air out though a bolt in the head that leads to the water jacket (odd how the factory service manual did not make any note of this, I had to figure it out on my own). Than it cooled just fine. Once you are certain all the air is bled out of the system you have to determine if coolant is circulated though both sides of the heat exchanger. Are you sure the heat exchanger is large enough? Even so, if it was too small but operating properly it would only heat up under heavy load (high demand on the cooling system). So it sounds like you are not getting any cooling at all if it spurts coolant out in only 5 min. Something is preventing cooling of the water, likely air bubble, could be blockage somewhere (not very common).

    Good luck.
     
  11. thudpucker
    Joined: Jul 2007
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    thudpucker Senior Member

    Ashley, start a new thread with your problem.

    Check the outflow of coolant water. You have a blockage somewhere and it could be parts of the older Sea Water impeller that came apart and lodged in places you cant see or get to, in the Cylinder block.
     
  12. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Right Ashley, the system you described is the standard configuration to which my comments refer as well. Unfortunately you didn´t understand the function of the "shunting". If you take away the thermostat, you leave both outlets from the thermostat housing open. One (often in the bottom) leads directly back to the circulating pump inlet. The other (often in the housing cover) directs the fluid to the cooler/heat exchanger.

    So, with the thermostat removed, the cooling fluid will take the route of least resistance, which is directly back to the pump. ERGO: DON NOT RUN THE ENGINE WITHOUT THE PROPER THERMOSTAT, UNLESS YOU PLUG THE SHUNT LINE!

    Now to the sea-water part. You have not mentioned how the reverse gear and engine oil is cooled. In basic systems, like yours, the water from the strainer goes to the impeller pump, then to the gear oil cooler and to the engine oil cooler, before it passes the main heat exchanger (if there is an intercooler, it should have the coldest water, hence be place directly after the pump).

    The two oil coolers in series with the main heat exchanger are often full of minor barnacles; their larvae passing the strainer without difficulty. This is also where surplus pieces from a destroyed rubber impeller will end. Since this occurs on the pressure side of the pump, you won´t notice any disturbance just by looking into the strainer. First of all, then: make certain that you have full flow through the sea-water system!

    And Thud: there is no connection where rubber pieces from the sw pump can find their way into the cylinder block!!!!
     
  13. CDK
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    CDK retired engineer

    Baeckmo, the 1.6 engine has no oil cooler, no intercooler and probably the gearbox also has no cooler installed.

    The strainer in the water intake may be a source of problems because it can become clogged. I did not install it but use brass scoops (Wasserlöffel) with a row of narrow gaps that can easily be cleaned under water with a wire brush.

    Ashley writes in post #24 "The block has just been tested and reconditioned."
    That means all hoses have been removed and reinstalled. The big question is: have they all be connected properly?

    A $25 infrared thermometer can provide the answer by checking hose temperatures during warm-up. The loop through block and head warms up first until 80 C. is reached, then the heat exchanger joins the game.
     
  14. baeckmo
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    baeckmo Hydrodynamics

    Yepp I know this one has no intercooler, but as for the rest, it varies between "marinizers". Just last week we drydocked a boat with a naturally aspirated VW four, marinized with the Bowman manifold AND a separate engine cooler AND a cooler for its Technodrive gear.
     

  15. jonr
    Joined: Sep 2008
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    jonr Senior Member

    > I have not found any restricted passages in the cooling hoses

    I was thinking inside the block. Some type of reverse high pressure or chemical flush might help.

    I have a theory (ie, never tried it) that one can test for internal air bubbles by pressurizing the system and then opening a valve - if there is air in there, then water will squirt out as the air expands. If it is all water, then there is no compression (except for perhaps rubber hoses) to expand. So very little "squirt".
     
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