Heat Exchanger - testing with a cheap alternative

[Mithril Bham]

Ridiculous price. Find an old engine and pull the heat exchanger (take it to a radiator shop and have it tested) or buy one for less that 1G. Pretty easy to install. Ones for small marine engines were invented here in Bellingham, WA by Orca from what I've heard.

[HankOnthewater]

Hi Tim
I know the Roberts 25 well, but the one I know had a small Yanmar diesel.
I suppose an outboard might serve you well while you sort out the diesel engine. An outboard bracket will fit next to the rudder, but will be really low and difficult to steer/throttle. A 3 to 5HP unit might be enough, to get in and out of a harbour.

The previous posts all gave good advice and the prices your mechanic quoted will buy you nearly a new boat. The prices indicated by posters here are much closer to the mark I would say, except for I don't know the Sole setup.

Although I am on the other side of Oz, I have an engine (water) and gearbox (oil) heat exchangers you can have. Maybe a little big (from a 39 HP engine). Both worked well when I took that engine out.

[GILow]

The prices quoted sound about normal for Australia to me. I didn't say they were OK, just normal.

In the OP's situation I would stop and have a really long think about this one. If the diagnoses of insufficient anti corrosives in the coolant is correct then the engine is most likely a small time bomb. And no amount of test runs are going to reveal the issues, what will reveal the issues will be a hard slog into the wind, or a messy approach to a harbour, or some other boating manoeuvre where it matters whether the engine is ok. That's when it is going to fail from internal corrosion. Therefore, any money spent on a heat exchanger, no matter how economical, may well be wasted money.

Certainly I would not spend any significant money on the engine, and since pulling it apart to see how much damage has been done will be a very significant cost there's a bit of a catch 22 here. If you can do the work yourself the at least that problem will be reduced but even a gasket kit for the engine could run to hundreds of dollars and the OP has indicated a limited level of experience which to my mind suggests a home job is not an option, not as a learner on a marine diesel anyway.

I agree that an outboard on a Roberts 25 will not be great, but if budget is tight, this may be about the only way to get a TRUSTWORTHY engine on the boat. Performance will be limiting, grip will be a problem, and if you have to throw a set of remote controls into the equation it is going to be the better part of the quoted replacement cost anyway.

One thing I would consider is seeing if a replacement engine of the same make and model can be found cheap enough to warrant a pre installation checkup. A 10hp is not going to be a monster to handle and you could easily drive it around in the back of a station wagon to a non marine diesel mechanic for a checkup first. If you get lucky and find a good one then replacing like for like should be a pleasant and rewarding project that will bring you much confidence in both the engine and your ability to maintain it into the future. This is the approach I have taken with our engine when I purchased a decent short block and injectors from a truck wrecker to keep on hand for an emergency. If our elderly engine dies tomorrow I will just strip off the marinisation components and fit them to the new block. The block is in the attic wrapped in industrial glad wrap. It was bought for less than it would cost to have a marine diesel mechanic visit our boat.

Matt


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[Mithril Bham]

Although GILow may be absolutely correct bad heat exchangers (and elbows) are very common. I have replaced many of them but check the engine out as well obviously. Think about an oil analysis.

[Frogster]

Why not just bypass the Heat Ex and go straight Sea Water cooling?

[GILow]

Originally Posted by Frogster

Why not just bypass the Heat Ex and go straight Sea Water cooling?

Well, that would one way of finding any corroded internal components pretty quickly.

Seriously though, not many engines are suited to that form of cooling, and you'd need to drill in mounts for sacrificial anodes etc in the cooling passages. Also the water jacket is probably optimised for high volume water flow at a pretty high water temperature, you pull raw water in and you'd most likely end up with a huge temperature gradient across the engine block, which pretty well begs for a cracked head or failed head gasket.

Not a retrospective change I would make lightly.

Matt

[Timinbondi]

So I finally got out to the boat to have a look. The radiator cap was rusted on and covered in a white gunky residue. Freshwater side has some pasty residue in it and was otherwise dry. I'm guessing it's been overheated. I could feel some of the residue in the head when I put my finger in the coolant port.

Wondering what to do now:
1. Pull the engine out
2. Try and flush it out.
3. Take the head and heat exchanger off and take them somewhere.

The mechanic said they started it which couldn't have been good with no coolant in it.

[Timinbondi]

Thanks for the offer Hank..I could sail over and get it maybe
Great replies all round.

[arsenelupiga]

this is what I would do:

take diesel out what can be taken out easily.

Install outboard. Looks good enough to me

[RaymondR]

Radiator caps are just pressed metal and pretty thin compared to the metals in the engine, the deposits inside could be residues from the evaporated coolant whatever it was.


The first thing to do is give it a good clean up and get rid of as much rust and gunk as possible.


If it's running I would then fill it with fresh water and run it until it was hot then shut it down and drain the fresh water out. Wait until the engine cools down and then refill, run and drain it and see if that gets rid of the deposits.


Fill it with the proper coolant and run about the harbour for a while and see if it overheat or if there is any water in the oil and if not and the engine does not overheat you might be OK.


I would not go near that mechanic again, he sounds a bit expensive and advising you to throw away what may turn out to be a perfectly serviceable engine sounds a bit extreme to me.

[SeaSon]

Fill the freshwater side with water or coolent. Vent if required by your engine design/operator manual. Check for visible leaks and correct. Start engine. Verify water coming out of exhaust (impeller pumping saltwater) If not, change impeller. Restart engine, Let run for 5 to 10 minutes, add more water, install new cap. Check and correct any visible leaks while it runs.

Run engine observing temperature until normal hot plus 10 minutes or it appears it is going to over heat. Let cool, remove cap. IF much water is missing from heat exchanger, then exchanger is leaking water from fresh to salt sides and requires replacement. IF still full of water, no leak, so begin flushing and cleaning operation.

Do the cheap and easy stuff first.

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[GILow]

I have no problem with them running then engine without coolant, provided it was not run for too long. Less than a minute should be plenty safe, and a very good idea to inform yourself of the overall condition of the engine before throwing expensive coolant additives etc.

[Timinbondi]

I managed to get the heat exchanger off on the weekend. I also tried to remove the head but couldn't budge it after I removed all the bolts I thought were necessary. Is there some trick to it? Does anyone know what Mitsubishi engine it is based on?

Attached is a photo of the radiator cap.

[SeaSon]

Why are you taking the head off? That should be the very last thing you mess with if at all. Yes the cap looks nasty.

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[Timinbondi]

Well there is this gritty gunk in the head too and a rusty residue. I also thought given it looks like its had a solid overheating it might be warped and should be reconditioned.