Engine problem - please help us diagnose what's going on...

Rivers & creeks

Rivers & creeks

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I hope we can solve this. Here's the story so far. We have a Thornycroft 230, works well, very little smoke. Compression tested 18 months ago and compression about 90% of 'new' level.

Suddenly on Friday we had a large amount of white smoke from the exhaust that turned out to be steam - vaguely present at tickover but lots at 75% revs. Stopped engine, checked raw water strainer and found plastic in it, we removed that and restarted and all the steam disappeared.

Next day no problem. Sunday we had steam again! This time we thought we traced it to a slightly crushed exhaust hose that injects the sea water into the exhaust elbow. Replaced and carried on.

Today did a routine check in the engine room after the engine had been running for 15 minutes - smell of burning and the inside of the Jabsco raw water pump was literally red hot! It's the centre cut away in the photo. We stopped the engine and a biggish puff of smoke came out.

View attachment 33902

We checked the raw water filter and it was packed with fine weed. We emptied, cleaned and restarted but the steam was back, lots at high revs, almost none at just over tickover up to 1000 revs.

Things we've done over the last few days:

Changed impeller.
Checked raw water seacock inlet
Removed stack and cleaned it (perfectly clear)
Emptied and refilled fresh water
Engine oil and fresh coolant checked every time we set off, unchanged.
Exhaust elbow removed last year and very clear.

Last year we replaced the main water pump. We were getting squealing noises like a slipping belt, but noises suspected to be from the water pump which was a bit rumbly when we took it off. Noises came again this weekend so maybe they were coming from the Jabsco? Hard to tell with a big old lump chugging away.

So any ideas why we're steaming? Was the Jabsco knackered today? We're holed up in Brighton on our way West and advice, suggestions and questions are very welcome,

Simon
 
Last edited:
Lazy Kipper said:
I hope we can solve this. Here's the story so far. We have a Thornycroft 230, works well, very little smoke. Compression tested 18 months ago and compression about 90% of 'new' level.

Suddenly on Friday we had a large amount of white smoke from the exhaust that turned out to be steam - vaguely present at tickover but lots at 75% revs. Stopped engine, checked raw water strainer and found plastic in it, we removed that and restarted and all the steam disappeared.

Next day no problem. Sunday we had steam again! This time we thought we traced it to a slightly crushed exhaust hose that injects the sea water into the exhaust elbow. Replaced and carried on.

Today did a routine check in the engine room - smell of burning and the inside of the Jabsco raw water pump was literally red hot! It's the centre cut away in the photo. We stopped the engine and a biggish puff of smoke came out.

View attachment 33902

We checked the raw water filter and it was packed with fine weed. We emptied, cleaned and restarted but the steam was back, lots at high revs, almost none at just over tickover up to 1000 revs.

Things we've done over the last few days:

Changed impeller.
Checked raw water seacock inlet
Removed stack and cleaned it (perfectly clear)
Emptied and refilled fresh water
Engine oil and fresh coolant checked every time we set off, unchanged.
Exhaust elbow removed last year and very clear.

Last year we replaced the main water pump. We were getting squealing noises like a slipping belt, but noises suspected to be from the water pump which was a bit rumbly when we took it off. Noises came again this weekend so maybe they were coming from the Jabsco? Hard to tell with a big old lump chugging away.

So any ideas why we're steaming? Was the Jabsco knackered today? We're holed up in Brighton on our way West and advice, suggestions and questions are very welcome,

Simon
Click to expand...

Is the usual amount of water coming from the exhaust outlet?

Maybe the Jabsco shaft has sheared or seized if there isn't, or the impeller is slipping on the shaft so less water is being pumped?
Ian
 
Hard to tell, it seems like an OK amount of water. When the innards of the Jabsco were red hot, just before I switched off I glanced at the raw water feed and there was water going through.
 
Perhaps some of the weed made it further into the system. As above says, Is the flow of water out of the exhaust normal? If not then you must have a blockage. First suspect would be the tube nest on the cooler.
 
Sounds like there's damage to the pump/impeller after running with the blocked filter. With reduced flow, the engine must be overheating and turning all the water to steam, less at low revs more at high revs. When you strip the pump, don't forget to ensure you get all pieces of vane out of the system or the partial blockage could just perpetuate the problem. Some engines tend to collect broken vanes in the heat exchanger stack. Let's hope the bearing and seals haven't burnt out, after all the water keeps them cool, too. Once fixed it would be a good idea to change the engine oil as it's probably gone above its designed temperature range.

Rob.
 
+1 to all of the above plus:

First check the coolant level. If low you may have a real problem. (head/block)

Otherwise & variously:

Disconnect the heat exchanger from the raw water inlet & outlet then run (hosepipe) water backwards through the heat exchanger to see if flow occurs

Rig a jury water supply to the water injection elbow, run her up and see if steam is *quickly* evident. If so it is not the raw water system

Rig a jury water supply to the heat exchanger inlet and thence to the elbow, run up and see what happens. In both cases, start the motor then turn on the tap, you don't want an hydraulic lock to add to the fun...

Remove outlet from jabsco & confirm flow volume and pressure if safe to do so. (may need to attach a length of hose to keep fingers away from belts. Don't overheat motor)

Reverse flow the raw water plumbing, you may be amazed at what comes out...
 
(Not an engine or installation I am familiar with).,,

EDIT: SAPurdies advice, above, sounds more methodical approach to try first..

Could it be as simple as the water inlet inadvertently being not fully open?(loose handle)
Or the water pump drive belt too tight?
Probably worth detaching the hoses at the pump and A observing water flow 'in' and B blowing air through the outlet hose using the dinghy pump, to see if there is untoward resistance.
And of course removing the impeller and free turning the spindle by hand.
..and is the syphon break ok and a collapsed hose right ' there'?
Of the two commercial engineers in Brighton, Mick West is I suppose the one some people prefer though there are Independents in the town much liked. Ask on the Mobo forum perhaps?

At least you are in Blighty not some furreign cove.

Btw if needed, I bought seals and bearings for my jabcso from a bearing place on a trading estate on Portland Road, Hove. 24hr wait I think and CHEAP . Best o luck

AND Finally, there was a very strange mystery blockage on a Rustler, turned out to be a Organic growth actually growing in one of the rubber tubes! Ooer
 
Last edited:
Lazy Kipper said:
The strange thing is the engine didn't overheat, it nudged up from its usual 82 to 86 degrees.
Click to expand...

I'd be inclined to reverse flush it by connecting a hose to the exhaust elbow pipe and remove the impellor to see what comes out.

If the coolant level has not changed and as the temp gauge didn't go up much, the engine will be fine.
 
ianj99 said:
I'd be inclined to reverse flush it by connecting a hose to the exhaust elbow pipe and remove the impellor to see what comes out.

If the coolant level has not changed and as the temp gauge didn't go up much, the engine will be fine.
Click to expand...

We'll do that first thing. The red hot Jabsco pump innards thing - any idea how do I find out if that has caused damage to the Jabsco pump?
 
Lazy Kipper said:
We'll do that first thing. The red hot Jabsco pump innards thing - any idea how do I find out if that has caused damage to the Jabsco pump?
Click to expand...


Take the cover off and inspect the splines (if its that type). It's probably okay as it appears to be still pumping. I think you said it was belt driven so the heat would more than likley have been from the belt slipping when it got clogged up. Worst case scenario is the heat having damaged the shaft seal so check for leaks from the shaft area.
 
It's the pump that drives the flexible impeller so it's driven by the engine rather than the belt - well take the impeller out and check as much as we can - just not sure what I'm looking for! Thanks for the replies so far.
 
This looks like a gear driven raw water pump rather than belt driven.

The raw water being passed through the pump should keep it cool. I would suspect that the bearings are shot. The only other source of heat would be the internal drive gear that will be lubricated by the sump oil.

If it is belt driven, a slipping belt could cause the high temperature ..... but this is unlikely as the raw water pump belts are not usually heavily loaded, and hence don't slip much.
 
Lazy Kipper said:
View attachment 33905 Thanks for the reply. Yes gear driven not belt driven. If the bearings are shot, would that reduce the water flow? And why glow red hot when the strainer was almost blocked? New pump or easy bearing change?
Click to expand...
If its the pump I think it is then the bearing change is not too difficult. You will need a workshop/vice etc or be very imaginative.

If the pump really was glowing red hot then I would be very concerned about the bearings. There are usually two sealed bearings and the seals on the bearings won't be much good if the pumps been red hot.
 
When you say the pump was red hot do you mean it was actually glowing dull red, or hot enough to discolour paint, or hot enough to spit back when you spit on it.

None of these are good things but the first two indicate something seriously amiss and you need to find the cause before running the engine much more if at all.

Possibly a seized bearing being spun in it's housing would cause this.
 
The old Bukh raw water pumps had no bearings and the shaft was water lubricated.If yours is one of these lack of water would lead to overheating.
 
I seem to recall problems with the end plates in a jabsco, you can reverse the cover, can't quite remember how the internal plate comes out. Either will upset the seal round the ends of the impellor.
 
If the strainer is blocked, there would be no water flow and hence nothing to cool the pump. Any water in the pump would be pushed out to the heat exchanger or overheat to steam. The impeller would be destroyed too ... so check the number of blades on the impeller and look for any missing ones down stream, particularly in the heat exchanger.

If the pump has overheated, the shaft seal behind the impeller must be replaced, and probably both sets of bearings. If the shaft seal has been damaged you will see water dripping out of the tell tale hole behind the impeller and the shaft seal.

If the impeller has got hot, there is a very good chance that it no longer makes a good seal with the face plate, the back plate, or the sides .... hence the water flow would be significantly reduced, and it's possible it won't self-prime too.
 
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