Two-cylinder diesel: one hot, one cold!

[NevisDog]

I thought I was sooo clever, diverting half of the raw water cooling straight to the exhaust to increase running temperature, from a low blood-heat (barely warm) up to a more acceptable 80C (180F). Though this Lombardini AD290 twin cylinder has always been a slow starter, requiring six or eight attempts of the starter motor, it otherwise seems to run smoothly enough (at what seems a rather high idle) with enough power to drive us at seven knots under way, so it came as a shock this morning to discover that the fwd cylinder at idle is too hot to touch, while the rear cylinder remains almost cool.

I guess there are plenty of possible causes: blockage in cooling water to/from fwd cylinder jacket; no fuel to aft injector; lack of compression on aft cylinder; could even be the aft decompression lever is engaged... I wouldn't know. No idea where to start looking. Would Nigel Calder's book on diesel engines cover this sort of troubleshooting? Or is it possible that my deliberately reduced flow of raw water through the engine will never balance out the cooling?

[tkeithlu]

Sorry to hear it. You actually listed the places to start. Compression check, is Number 2 firing, fuel to #2, cooling getting to #2? Then condition of the injector. The back woods farm mechanic who taught me diesel basics tested them by clamping one in a vise, filling it with WD-40, and then hitting it on the top with a hammer. You got a fog out the bottom or you didn't. Crude but effective. From your problem with starting, you may have been running on one or 1 1/2 cylinders for some time. Basically, you've got either a firing problem or a cooling problem, and can do the things necessary to eliminate one and fix the other.

[Wotname]

First up I would be looking to see where the thermostat is situated in the cooling system.

But perhaps I would also be asking if this is raw water cooled engine rather than a freshwater cooled system (heat exchange etc).

If raw water cooled, you don't want to be increasing the water temperature inside the engine. It has to run below about 50C otherwise the salt precipitates out and clogs up the water galleries.

[Diesel Bill]

Sounds to me like you are on the right track with all you mentioned. Restore the cooling water to full flow and and then check fuel to the cold cylinder. Possibly a stuck plunger in the injection pump. Not really familiar with the brand. If it's running smoothly hopefully not a serious mechanical condition. Either cooling or fuel related. Good luck troubleshooting and let us know what you find.

[NevisDog]

Thanks for hint on testing injectors! But am I game to try it?

And yes, this engine is direct raw water cooled (no thermostat) so now I'm likely precipitating salt all over the inside. Now I'm aware of this I can adjust the inlet/bypass to keep temp below 50C.

But it has only been run for at most two hours since I reduced the raw water through the block, so any blockage must have been there already (and I'd never have known there was an issue if I hadn't increased the temp). Will begin by opening up the water jacket and takink a look inside - that's probably the least technical part anyway.

[Wotname]

Originally Posted by NevisDog

Thanks for hint on testing injectors! But am I game to try it?

And yes, this engine is direct raw water cooled (no thermostat) so now I'm likely precipitating salt all over the inside. Now I'm aware of this I can adjust the inlet/bypass to keep temp below 50C.

But it has only been run for at most two hours since I reduced the raw water through the block, so any blockage must have been there already (and I'd never have known there was an issue if I hadn't increased the temp). Will begin by opening up the water jacket and takink a look inside - that's probably the least technical part anyway.

No thermostat would be unusual but possible. I had a single cylinder Arona way back when and I thought it had a thermostat but can't be sure anymore.

Two hours isn't long enough to cause harm

You can flush a raw water cooled engine and I do this every few years or so on my Yanmar.

First remove any thermostat and zincs. Then flush with vinegar for about 24 hours or if you are bold enough, flush with hydrochloric acid (~20%) for maybe an hour tops.

I used a bucket of preferred flush, a cheap bilge pump and some hoses and circulated the flush though the engine for the required time.

Dion't forget to refit thermostat and zinc.

Don't pass the flush though the raw water pump.

[Wotname]

I think your engine has decompression levers (one of each cylinder ). If so, it is easy to tell if one cylinder is not firing properly. Operate each one at a time and note what happens. A good cylinder will immediately stop firing and the rpm will drop and the engine will vibrate noticeably. A poor cylinder will have little effect.

[GILow]

Originally Posted by Wotname

No thermostat would be unusual but possible. I had a single cylinder Arona way back when and I thought it had a thermostat but can't be sure anymore.

Two hours isn't long enough to cause harm

You can flush a raw water cooled engine and I do this every few years or so on my Yanmar.

First remove any thermostat and zincs. Then flush with vinegar for about 24 hours or if you are bold enough, flush with hydrochloric acid (~20%) for maybe an hour tops.

I used a bucket of preferred flush, a cheap bilge pump and some hoses and circulated the flush though the engine for the required time.

Dion't forget to refit thermostat and zinc.

Don't pass the flush though the raw water pump.

Strangely similar to descaling a coffee machine.

[NevisDog]

Thanks for all the help. I'll try posting a picture of this prehistoric beast tomorrow but yes those decompression levers should simplify things - should have thought of that! Raw water pump pipes straight into bottom of block, so there doesn't seem to be anywhere to fit/remove a thermostat - I assumed this was normal as the last few raw water cooled engines I had (many years back) were the same. I think this one is also around 30 years old.

[NevisDog]

Originally Posted by NevisDog

... Raw water pump pipes straight into bottom of block, so there doesn't seem to be anywhere to fit/remove a thermostat...

Okay so thermostat housing would be at the top somewhere, at the (hot!) exit point (Duh!) but there doesn't seem any likely spot on this engine. Pretty sure the old and tattered (pages missing/stuck together) manual doesn't show one either.

[Wotname]

Originally Posted by NevisDog

Okay so thermostat housing would be at the top somewhere, at the (hot!) exit point (Duh!) but there doesn't seem any likely spot on this engine. Pretty sure the old and tattered (pages missing/stuck together) manual doesn't show one either.

Yep, usually near the exit point because the raw water cooled (RWC) thermostat operation is a little different than that in a closed loop freshwater cooled engine.

A RWC thermostat has to divert the water away from the head and into the exit point so the exhaust system gets the same amount of water whether the thermostat is open or closed. Whereas in a closed loop system, the thermostat merely restricts the water flow.

[Wotname]

Originally Posted by NevisDog

Okay so thermostat housing would be at the top somewhere, at the (hot!) exit point (Duh!) but there doesn't seem any likely spot on this engine. Pretty sure the old and tattered (pages missing/stuck together) manual doesn't show one either.

It might not look like a conventional "thermostat housing". The Yanmar GM series and YS series aren't in an conventional looking housing.

2GM20 thermostat housing in the top LHS quadrant of picture.

[Wotname]

And a YSE-8 thermostat housing - green thingy at the centre top!

[out42]

Might have missed a comment about this but are both exhaust pipes equally hot? If so, it is cooling water blockage or restriction to the hot one. That narrows things down a bit. If they are different temps, then as everyone has said, injectors, decompressors, fuel blockage, etc. As you comment that it is plenty powerful, then it is probably cooling water uneven flow.

[NevisDog]

Originally Posted by out42

... are both exhaust pipes equally hot? ... If they are different temps, then ... injectors, decompressors, fuel blockage, etc. As you comment that it is plenty powerful, then it is probably cooling water uneven flow.

Will try to post a photo - both exhausts go to a sort of heat exchanger box on side of engine; forward half of exhaust box could fry an egg, while aft half remains cool (yet raw water from engine seems to enter about mid-point and exit from forward). So... this suggests fuel is not being burnt in aft cylinder???

But seemingly no rough running, no undue smoke, enough power... suggest no lack of fuel burning??? (Just the hard-to-start thing, plus slightly fast idle setting.)

I hate when two separate problems arise at once - is this one of those occasions? Will try to find out today. (Still can't see anywhere to fit a diverting thermostat but will keep looking when daylight strikes here.)