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The elusive 224/3.7 MerCruiser banger

Discussion in 'The Hokey Ass Message Board' started by tjm73, Apr 9, 2008.

  1. I saved too much weight on the alternator.
    The kubota ones would be ample if there was just a battery ignition needing power.
    Last edited: Sep 11, 2020
  2. Beck, I'm curious about your transmission also. Randy ran his motors up to 6800rpm for lots of power. Mine is usually chugs along around 2000rpm so I just want torque and an effective radiator.

    I worked out a reasonably easy way to clean the pickup tube on the oil pump.
    It works on the aluminum pumps as they have a center hole in the pickup screen.
    Thread a lawnmower throttle cable housing completely through the tube as it is flexible enough to go around the bends. Pull dental floss back through the pickup tube with the throttle cable housing.
    Tie a small rag to the dental floss so it is in the center of the floss. Pull the rag back and forth in the pickup tube with solvent but don't pull hard enough to break the floss or you will have to poke it out with the throttle cable housing that contains its wire for more stiffness. The hole in the screen is a screen bypass for when the screen is plugged. The hole is normally closed pressing against a strip of sheetmetal . Debris above the screen can be washed out or removed through the center hole with tweezers and pipe cleaners or q tips.
    Last edited: Sep 12, 2020
  3. Warpspeed
    Joined: Nov 4, 2008
    Posts: 532


    One other observation ..........

    Electric radiator cooling fans are now a pretty normal thing to see on many factory cars, but you will never see a factory fitted electric water pump.

    The wimpy little aftermarket water pumps being sold are just a gimmick, and just do not have the balls to raise internal engine water pressure to what is really required to work properly even on a stock engine.

    If it worked, the vehicle manufacturers would have been onto it a long time ago.

  4. Our reasons are not necessarily the same as theirs.
    Pump have different failure modes:
    Belt driven pumps must have the belt aligned, tensioned and not broken.
    Camshaft driven mercruiser pumps offer the problem of coolant leaking into engine oil.
    Electrical pumps wires can break or short out.

    Concerned about oil contamination, I changed to a belt driven pump, but the Mercruiser pump
    is a nicer design with efficient, gracefully tapered impeller blades. Compared to it a Toyota Corolla water pump's sheet metal impeller is cruder than that of the Mercruiser pump that it replaces and it does not appear to be capable of much force. If one wants more available power(temporarily) to drive the wheels, electrical pumps of course have an advantage. For comparison's sake, I'm going to build up one engine with a Mercruiser pump.
    I'd love to find an inexpensive electrical pump to try in comparison with the others.
  5. Warpspeed
    Joined: Nov 4, 2008
    Posts: 532


    Have to agree, the original Mercruiser water pump is a nice pump, compared to most others.
    But then, it has to be as its only turning over at half engine speed.
    The original design intention of eliminating the fan belt was good, but by eliminating one potential failure point, the leaking seal problem arguably created something far worse.
    Beanscoot likes this.
  6. I agree. Solving one problem created the problem of cross contaminating oil and antifreeze.

    Cross contamination could be eliminated by leaving open the drain for the chamber between the seals. I was surprised at how quickly the camshaft can be grooved by the seal lips. Grease normally specified in the chamber to aid sealing could also seal the drain so I'd omit the grease and leave the drain plug out.

    Impeller speed raises the question of power loss which should quadruple with speed doubling ( for this comparison to be valid, only the speed can change, everything else must remain unchanged).
    I can't say that Toyota pumps are better, equal or worse than the Mercruiser pump. I can say that they , with some adaptation, can be made to fit and they do pump water.
  7. tjm73
    Joined: Feb 17, 2006
    Posts: 3,379


    BMW's come with electric water pumps. Have for years. Mercedes too.
  8. tjm73
    Joined: Feb 17, 2006
    Posts: 3,379


    In 2010 (off topic I know...sorry) BMW 3.0 Turbo 5-series cars (300hp) had electric water pumps. Replacements are around $250-$300. When you say "inexpensive" what does that mean?
  9. Inexpensive is not $300. $30 is inexpensive to me, perhaps If you pull one yourself, one from a junkyard might go for that when the counterman is in a good mood.

    When I go to a yard and make an offer, I try to be fair to them.
    I lay what I think it is worth in cash on the counter next to the part.
    If he picks up the money it is his and the part is mine.
    If he smiles I put down too much money,
    If he looks like he is sucking on dill pickles, I got a little discount.
    If he shakes his head you have to lay down more money.
    Then you have to show him you don't have any more money
    He tells you nobody gets it that cheap but hands it to you anyway
    The thing is to be fair and nice.
    They have to pry money out of stingy people.
    They want the money and I want the part so the odds of a discount are in your favor.
    Last edited: Oct 2, 2020
  10. My oil pumps have taught me some things recently:

    The aluminum pump is a newer version but not available. The cast iron one is still made but it is quite heavy. You can run a swab on a string down the aluminum pump's pickup tube as there is a center hole in its screen. If you do that you will probably "spring" the screen so it no longer acts as a valve and you will need to plug it's hole I cold not find a stopper that I trusted to stay in the hole but an expansion plug, inserted upside down and used as a simple stopper should say in place. its center hole has to be plugged, rtv silicone rubber to the rescue.

    I could not find a new square cross section o ring for the pickup tube, but round cross section ones are available. I am trying one. It seemed a good idea to supplement it with high temperature rtv silicone rubber. The rtv mostly just created a mess which had to be removed. For the rtv to stick the surface must be oil free. The o ring by itself should be enough. You will need to have a new o ring as old ones get smashed out of shape. the O ring must be put into the channel it fits into if you assemble it on the tube, it will be at risk of having a chunk cut out of it if the tube is bolted up with its O ring squeezing plate at a slight angle.

    The pump cover is supposed to have a thin gasket, you can make one out of 0.0045 kraft paper from a small bag. The gasket will give the proper end clearance for the rotating parts in the geo rotor pump. The cover plate may become scored if no gasket is used and parts rub. If it has been running and not scored its cover you can skip the gasket as aluminum pump clearance opens up when they come up to temperature but cast iron pumps don't do this.

    The pump should be primed with oil through the pressure sender hole in the block. Filling it before bolting it to the block results in an oil puddle on the floor where you need to lay.

    There is a definite sequence to follow to connect the pump and pickup tube : 1 bolt the pump to the block 2. bolt the tube to the block 3. work the o ring into place 4. slide the o ring pressure plate in place and tighten its socket head bolts. The top one is easy but the bottom one (on aluminum pumps) may take magic.
    I will use very small vice grip pliers on it. RTV or a 0.020"thick paper gasket 3/4" ID and with 1" OD could back up o ring for a tighter squeeze on it. The area must first be squeaky clean for rtv..

    Replacing an oil pump is a simple job, easy if the engine is out of your car. Working under a car with an engine dripping oil is unpleasant..
    Last edited: Oct 2, 2020

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