Bavaria 38 engine cooling problems

[MASH]

Look at this logically...

Water flow is satisfactory at low revs ergo no restriction to water flow (at low revs)

Waterflow restricted (evidenced by turning it to steam) at high revs ergo restriction to flow is revs related


This can be due to only 3 things that I can think of.

1) Increased revs = increased suction from pump which is causing local collapse and flow restriction of inlet hose, hull side of pump.
2) Increased revs = ingestion of air via a leak which must by definition be on the hull side of the pump.

3) Increased revs = increased exhaust back pressure overpowering pump delivery, a problem downstream of the pump.

I think you can discount hull speed as being a factor but you'd prove that by running in gear alongside and showing the same symptoms.

So it can only be a suction (and therefore rev related) flow restriction between hull and pump or a backpressure issue on the other side of the pump. Can't be anything else, can it?

I say again, check your hoses under power. The collapse of an intake hose can be over just a centimetre or so of length right against fittings be they seacocks, pump intake or filter attachments. Feel the entire length of every intake hose between hull and pump, every last bit with the water delivery misbehaving as described. No point checking it with situation normal at idle. It will take some courage to do that - work fast but leave no piece of that hose untouched. Even slight necking or narrowness right up against the jubilee clips is a sign of the trouble.

I don't know how much you'd notice backpressure in the feed to the exhaust elbow by feel but that's the other most likely source of such problems, and as someone said above with cooling flow problems the exhaust elbow is the commonest suspect after filter/barnacle blockage.

 

[Bosun Higgs]

Thats my problem.(replying to vyv_cox) As you can read from my earlier posts, most of it upstream has been checked. The fact that the bubbles (assuming thats what they are) in the pipe downstream of the heat exchanger get more as the throttle increases tends to suggest air leakage into the system, I just cant find the source! I think it must be the seawater filter but as I said earlier ive already changed the bottom gaskets and the filter basket/seal. One of the problems with the volvo system is that the hose from the seacock to the filter is a different diameter to that going from the bottom of the filter to the engine pump so getting a replacement filter is not straightforward as most have the same diameter inlet/outlet. Ah well,I cant go sailing in this weather so at least I have time to get it sorted, and thanks everyone for the suggestions. I was really hoping to find someone else who had the same problem who had effected a fix, and one guy has said he has the same problem but also hasnt managed to fix it yet.

I agree with Vyv's logic - air will not be getting into the system upstream of the pump. So if it is air, then its getting in between the sea and the pump. Personally I would try to prove this to myself by connecting a fresh pipe from the seacock to the pump direct and running the engine for a short period without filter. If that works OK then you need to revisit the components between cock and pump. If you still have bubbles then its steam and the problem is insufficient water flow either because of the feed into the exhaust or because of a blockage further back.

An alternative way of checking the system through to the pump is to use duct tape to tape up externally all the joints between cock and pump inlet. I've never had the air leak into water issue but I have had the air leak into diesel problem. I taped up all the joints to prove that there was an air leak and then undid the tape joint by joint to isolate which joint it was.

 

[iainbluk]

Thanks guys I will check all those things again when I get down to the boat in a week or so.

 

[MASH]

For it to be an air leak as huge as that I'm sure the suction would be clearly audible, it would be easily detectable by touch and the hose would leak water when shutdown too. Also the water in the clear hose between pump and exhaust elbow would not just have a few bubbles in it as reported, a normal condition imho, but would look like beer froth, ie more air than water which is just not what's been described.

The more I think about it the more I think this is an intake hose that is collapsing under high revs and restricting flow. That way you'd get pure water in the pump-elbow line with perhaps some bubbles of un-dissolved air and no other symptom.

Interested to hear the result.

 

[iainbluk]

The intake hoses are all wire reinforced and have not noticed a collapse but one hose is quite difficult to see. Will try and take some pics and post on here if I cannot resolve it.

Will report back as soon as I have some more info. Thanks for your interest!

 

[MASH]

Ian, if a collapsed hose is the trouble your fingers will tell you - a hose that goes from circular to even "flattish" is a potential problem, but check them first to see how they are cold, engine stopped and then get the engine into it's steaming exhaust range and recheck quickly before you get an overheat. If its there your fingers will tell you.

I'm going on about this because the other options are big effort and possibly cost - this one is not, so eliminate it first.

 

[VicS]

The intake hoses are all wire reinforced and have not noticed a collapse but one hose is quite difficult to see. Will try and take some pics and post on here if I cannot resolve it.

Will report back as soon as I have some more info. Thanks for your interest!

I was think along the same lines as MASH a collapsed hose somewhere....... de-laminated so that it is obstructed internally without anything being obviously wrong from the outside. Not necessarily one of the inlet hoses.

Normal flow at idle but reduced flow at higher engine speeds is a symptom of a de-laminated hose.

 

[bluedragon]

Interesting thread. I've been suffering from the same problem with my 2020 ie. a reduced seawater flow at high RPM only. It's not the heat exchanger or elbow (both been off and checked - completely clear). Checked the saildrive inlets from both outside and inside - no blockage that I can see. I hadn't thought about air getting in on the suction side of the pump, or a collapsed hose, but I'm pretty well convinced my problem is feed related. An air leak at the seawater filter is the first thing to check. I'll bypass it this week and see what happens. I've also thought of running a hose from the sink outlet cock straight to the pump, thereby bypassing everything.

 

[iainbluk]

Let us know how you get on!

Interesting thread. I've been suffering from the same problem with my 2020 ie. a reduced seawater flow at high RPM only. It's not the heat exchanger or elbow (both been off and checked - completely clear). Checked the saildrive inlets from both outside and inside - no blockage that I can see. I hadn't thought about air getting in on the suction side of the pump, or a collapsed hose, but I'm pretty well convinced my problem is feed related. An air leak at the seawater filter is the first thing to check. I'll bypass it this week and see what happens. I've also thought of running a hose from the sink outlet cock straight to the pump, thereby bypassing everything.

 

[savageseadog]

Overheat

The Barvaria has a sail drive doesn't it?

Had a similar problem with our Yanmar when the intake grooves on the leg became slightly blocked with growth. On the SD20 the larger intake on the underside the leg running up the inside leading edge is the one that the barnicles and **** really get into & the one some forget to clear.

Run the engine with the intake in a bucket - bet its ok.

 

[iainbluk]

Thanks seadog. If you read the opening post you will see that I had the boat lifted last week and checked the sail drive including rodding up the leg to ensure no blockages.

The Barvaria has a sail drive doesn't it?

Had a similar problem with our Yanmar when the intake grooves on the leg became slightly blocked with growth. On the SD20 the larger intake on the underside the leg running up the inside leading edge is the one that the barnicles and **** really get into & the one some forget to clear.

Run the engine with the intake in a bucket - bet its ok.

 

[bluedragon]

Yes, I will. Might be around mid-week.

 

[Playtime]

Does your system have an anti syphon valve in the seawater inlet? My previous boat (Bavaria 38 Ocean) had an MD22 (same base engine as the D2-55, I think) and was fitted with a Volvo anti syphon valve between the filter and the pump. This used to let air in unless regularly cleaned/checked. I replaced it with the Vetus equivalent which was much more reliable.

The second problem with the seawater system was the Volvo large black filter. No matter what I tried this always let slight amounts of air in. Again, I replaced it with the Vetus version and had no further problems.

 

[bluedragon]

Let us know how you get on!

Did some tests today. Firstly, I suspect the problem has gone! The amount of water coming out of the exhaust is now proportional to the RPM (it never was in the past). It could be that using a coat hanger to rod-through the saildrive from top and bottom might have shifted something (though I couldn't feel any blockage), but more likely is that I have now made sure that the seawater filter is properly seated in its unit and the cap in on tight. If I release this then a lot of air is obvious in the pipes. So fingers crossed.

 

[iainbluk]

Hi Playtime. Thanks for the suggestions. My anti syphon valve is between the heat exchanger and the exhaust I think. But I am interested in your comments about the black volvo filter which I am going to temporarily bypass for a run next week and see how it performs before I buy the vetus one.

Does your system have an anti syphon valve in the seawater inlet? My previous boat (Bavaria 38 Ocean) had an MD22 (same base engine as the D2-55, I think) and was fitted with a Volvo anti syphon valve between the filter and the pump. This used to let air in unless regularly cleaned/checked. I replaced it with the Vetus equivalent which was much more reliable.

The second problem with the seawater system was the Volvo large black filter. No matter what I tried this always let slight amounts of air in. Again, I replaced it with the Vetus version and had no further problems.

 

[iainbluk]

Well done bluedragon !

Did some tests today. Firstly, I suspect the problem has gone! The amount of water coming out of the exhaust is now proportional to the RPM (it never was in the past). It could be that using a coat hanger to rod-through the saildrive from top and bottom might have shifted something (though I couldn't feel any blockage), but more likely is that I have now made sure that the seawater filter is properly seated in its unit and the cap in on tight. If I release this then a lot of air is obvious in the pipes. So fingers crossed.

 

[bluedragon]

Well done bluedragon !

Yes, bypass that black seawater filter. I'm pretty sure now that was the cause of my problem. BTW my anti-siphon valve is on the high pressure side of the water pump (between pump outlet and heat-exchanger) so I don't see how this could suck air in (unless somebody can explain). Actually a question to all - is that the right place for it?

The water flow from the exhaust at 3000rpm is now vastly greater than before. I haven't run the engine up to high rpm for a long period yet to test the theory, but I think it's problem solved.

Good luck.

 

[Tranona]

Yes, that is the right place for it. The alternative is in the pipe between the heat exchanger and the injection point to the exhaust , but the smaller engines don't have a hose to break into. It does its job of sealing when the pump is pressurising the pipe and releases when the pump stops. Air can get in if the little flap inside is stuck in the open position, although normally they fail by sticking closed and so not breaking the syphon when you want it to! Difficult to tell from outside whether working correctly as the vent tube goes down to the silencer, so worth cleaning regularly.

 

[nigelmercier]

Yes, bypass that black seawater filter...

I discovered that one of the copper pipes on my filter was badly corroded and had pin-holes. I made a replacement with some copper pipe and a solder fitting cut to length to provide the step.

 

[Bav34]

Yes, that is the right place for it. The alternative is in the pipe between the heat exchanger and the injection point to the exhaust , but the smaller engines don't have a hose to break into. It does its job of sealing when the pump is pressurising the pipe and releases when the pump stops. Air can get in if the little flap inside is stuck in the open position, although normally they fail by sticking closed and so not breaking the syphon when you want it to! Difficult to tell from outside whether working correctly as the vent tube goes down to the silencer, so worth cleaning regularly.

That's interesting

On my 34

Pipe 1 runs from the seacock to the black filter
Pipe 2 runs from the filter to the pump inlet
Pipe 3 runs from the pump outlet to the syphon
Pipe 4 runs from the syphon to the heat exchanger.

Sorry forgot to add ... was going to suggest joining 1 to 2 to bypass the filter as a test.