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Old 06-02-2014, 01:12 AM
shawnb shawnb is offline
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no water flow, engine overheats

This is a continuation of my rebuilt engine install.

Well, I made progress today and installed rebuilt A4 in boat. The problem is no water flow in exhaust. White vapor steam coming from exhaust.
During the rebuild I replaced the water propeller and cleaned pump.
Raw water is making it to pump and water is in engine block. Here is the newbie stuff I did when installing the engine and possibly causing what appears to be a failed water pump.

Started engine but had exhaust valve turned off. Engine was hissing and blowing and probably created a lot of back pressure. turned on valve and exhaust, Yippie but no water

Thought blockage might be thermostat(I tested this before installing)So I flipped it over. I thought this fixed problem...water started dripping out...very low flow. one note: when I flipped thermo over and inspected head it was bone dry in cavity.

Not enough water, so I removed thermo success.

My question now is: could I of cause a vapor block or airlock by not having exhaust valve and thermo in correct position? And once corrected now have no water flow?

What steps do I take to get water flowing and engine temp correct?

How can my water pump fail? The only wear part is propeller and this is new?

Also, I ran the engine for probably 15 minutes....not realizing my 220-240 degree engine temp issue)newbie).......have i damaged the engine now?

After engine cooled a number of times it started right up but not under load.
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Old 06-02-2014, 06:35 AM
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Marian Claire Marian Claire is offline
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There have been many reports of A-4s being overheated and suffering no damage. Hope that is true here. You mention changing the water pump impeller. Did it fit snugly? Some have experienced a lose of flow due to a slightly small impeller or a correctly sized impeller placed in a worn pump housing. I would disconnect the line from the output of the water pump and check for flow there. No help on the back pressure issue. Dan S/V Marian Claire
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Old 06-02-2014, 06:48 AM
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Mo Mo is offline
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Hi Shawn,

Close raw water thru hull valve and remove hose. Open slowly and see if water comes in there. If so fill hose with water and quickly place it back on...OR if you have a "t" fitting for winterizing you can prime the pump from there. The pump might need priming. If the impeller was replaced recently it's probably not the problem and I wouldn't haul that apart there just yet.

Because you saw steam I have to think there may be more to this:

-remove the T-stat completely for now because if it is debris you want it to be blown on through the system.
-at the exhaust end of the manifold there, where the hose comes off and goes to the hot exhaust...remove the hose at the manifold and see if there is rust or crud there...I have used a coat hanger to clear those. Put it back together and try it.
-if none of that works there may be an old part of impeller or rust blocking up a circulation elbow, again it will need to be cleared.

Just a note, last week I was working on a friends Yanmar and it wouldn't circulate...after couple of hours of pure misery I used my air compressor and back pressured the whole thing. To do this I disconnected between pump and engine and at the manifold...for A-4 I suggest T-stat side...can always clean out manifold fitting itself. I couldn't believe the crud that came out. With that engine I removed T-stat; disconnected from pump and hot exhaust and just gave'er. Give a shot through exhaust as well to ensure clear. Put it all back together and pumping fine.

Hope that helps.

1976 C&C 30 MKI

The pessimist complains about the wind.
The optimist expects it to change.
The realist adjusts the sails.
...Sir William Arthur Ward.

Last edited by Mo; 06-02-2014 at 06:58 AM.
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Old 06-02-2014, 09:09 AM
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JonnyQuest JonnyQuest is offline
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Hi Shawnb,

I know people are throwing all sorts of (excellent) ideas at you, and they are truly experienced Afourians. I'm a novice but can relate my water flow issues from a couple of seasons back.

Had low flow coming out of exhaust thru-hull (transom exit), but not too bad in beginning of season. Water temp slowly started to creep up over the weeks. Removed and cleaned T-stat and tested in pot on stove--no problem. Put T-stat back on and either flow was then completely blocked up or it became completely blocked by the next time I started the engine the following week--I guess my T-stat maintenance dislodged some crud that flowed downstream to form a blockage, which I would find later.

Tried to do a pressure wash, per MMI manual and forum instructions, and was not getting anything out the exhaust outlet. Decided to work backwards from the exhaust outlet:

1. Long stick up exhaust transom fitting--no blockage.
2. Removed exhaust hose from manifold to mixing elbow (figured I can tackle exhaust iron piping later if still poor flow). -- Found blockage-- rust, scale, etc. completely blocking the fitting coming out of the manifold, COMPLETELY sealed shut! Wire hangar to attack and remove build up allowed for some flow now, but obviously all that came from the water manifold, so it was likely rusted and scaled up too.
3. Removed intake hose to water manifold (high side of engine) and not as bad. So I poured vinegar into the manifold until it filled up and let it sit for a week or so. Then came back, cleaned out with wire hangar at both ends again (over the week I also soaked and cleaned the in and out elbow fittings) and performed the pressure flush procedure for about an hour--on, off, on, off. -- pushed out a TON of loosened rust, scale, etc. Quickly turning on/off the pressure flow for the water helped to dislodge any remaining crud.

From initial pressure water bursts to final, flow increased dramatically to essentially no apparent restriction in flow as water passed through the water manifold. (Used clear tubing to aid in seeing the crud coming out of the manifold, and clarity of water in the end)

I don't recall whether I followed up with an acid bath the same season or the following season, but certainly the vinegar addressed the problem for me.

Notice that I didn't stop scratching my head and actually find my problem until I systematically back-tracked the water flow from the exhaust thru-hull. It pays to systematically attack a vexing problem.

Let us know how your troubleshooting goes.


NOTE: I've never had to reprime my water cooling system as Mo discussed, don't know the first thing about that myself. --In case that is your problem.
Boatless right now.
(Last boat, a fine 27' O'Day 1975)
MS Gulf Coast

Last edited by JonnyQuest; 06-02-2014 at 09:13 AM. Reason: typos!
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Old 06-02-2014, 11:31 AM
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Marian Claire Marian Claire is offline
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"It pays to systematically attack a vexing problem."
Well stated JQ.
The choice of where to start, exhaust thru-hull or RW intake thru-hull is up to each person. Just follow JQ's advice and move thru the system one step at a time.
Dan S/V Marian Claire
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Old 06-03-2014, 04:55 PM
shawnb shawnb is offline
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Problem Solved but more questions about cooling system

For some reason the previous owner removed the water pump cam and I didnt know it was missing because I didnt know it needed one. I found the item in the online catalog when looking at new water pumps. Fortunately I had a second water pump from old engine, its an ITT model with a much smaller impeller than ones available in catalog.

Oh and now I have great water flow and a cool engine. a couple questions though;

The water jacket side plate is missing the nozzle fitting used for directing water to rear cylinder? Is this a big deal, without end cap it will shoot straight into the cylinders between 2-3.

Does anyone no where to get the impeller for what I am guessing is off early model A 4. The manufacturer is ITT.

Making good progress, I now have a running engine in my boat. 4 months ago I had 40 engine parts sitting in a basket....
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Old 06-03-2014, 05:47 PM
Dave Neptune Dave Neptune is offline
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Exclamation Yep should be there

shawnb, yes the diverter is a good idea for proper circulation and even cooling.

Check with Ken on the numbers on your pump. This will insure getting the correct impeller, if MMI does not have Ken can probably still give you a contact and a good number for the impeller. ITT is just another of the many that will work, however the correct impeller is a must. And there is always the new improved pump from MMI too.

Dave Neptune
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Old 06-04-2014, 12:16 PM
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sastanley sastanley is offline
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shawnb, that diverter is nothing more than a $5 bronze/brass pipe thread cap that you can drill yourself, if it is a late model side plate. Usually, it is 3/8" NPT.

Congrats on getting the motor running!

"Twice Around" - '77 Catalina 30, #511 with original A-4 & MMI manifold.
She is even happier with fresh paint on the topsides!
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Old 03-24-2017, 08:10 PM
offtosea offtosea is offline
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scale /cleanout

thanks for the cleanout idea,will try the vinegar,and blow back,It has become difficult to run the engine comfortably with the clogging
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Old 03-29-2017, 03:41 PM
Offtosea07 Offtosea07 is offline
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Good riddance winter,almost,Is it harmful to t he engine to do a vinegar soak,hear mixed views,the best way to clean out manifold is ?
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Old 03-30-2017, 01:15 AM
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Originally Posted by Offtosea07 View Post
Good riddance winter,almost,Is it harmful to t he engine to do a vinegar soak,hear mixed views,the best way to clean out manifold is ?
Welcome to the forum.
You ned to start a new thread and explain the problem. You will get way more responses and ideas.I get the impression you have poor or no water circulation and you suspect the trouble is in the manifold? If you have a 90*elbow at the outlet these are famous for plugging up.
Are you getting any water circulation through the manifold at all? The answer to your question R\E the best way to clean out the manifolds is to take it off the boat and hot tank it. The next best way is to physically remove as much KRAP as you can then if you can establish flow circulate vinegar through it with the pump, inlet, and outlet hoses in the same bucket with the flow going the opposite way the water is circulating now. Vinegar is a mild acid and will not corrode the metal even if it is in contact for an extend period. Plus your boat will smell like a salad!
Hope this helps.


Last edited by JOHN COOKSON; 03-30-2017 at 01:56 PM.
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