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

Thanks for those replies. The pump itself wasn't red hot but in the first picture there's a slot in the middle of the pump, inside that I could see a red hot spinning disc. The water was still flowing but obviously restricted. The impeller is fine, we checked last night. After clearing the weed the pump ran and water flowed but there was the steam at more than 1000 rpm. There's no dripping in or around the pump.
 
Then I would be undoing that pump next from its gear driven back mount and turning it by hand with the impeller removed and see what the resistance and play are like in the bearings ...
Perhaps a call to the supplier of the pump exchange unit too for their experience?
The impeller definitely, definitely engaged with the peg or slot when put in and the fins definitely definitely have the same stiffness and unworn ends as a brand new one in the spares box?
 
Lazy Kipper said:
Thanks for those replies. The pump itself wasn't red hot but in the first picture there's a slot in the middle of the pump, inside that I could see a red hot spinning disc. The water was still flowing but obviously restricted. The impeller is fine, we checked last night. After clearing the weed the pump ran and water flowed but there was the steam at more than 1000 rpm. There's no dripping in or around the pump.
Click to expand...
Have you taken the pump apart?I would start with that.One reason for steam on the exhaust is too little water being injected into the exhaust.Not being enough to cool the gases it turns to steam.Is the exhaust manifold clear?
 
Hypothetically: What happens if a downstream, partial restriction restricts pump throughflow at anything over 1000revs. Would that be enough to create the symptoms observed on the pump itself?
 
Blueboatman said:
Hypothetically: What happens if a downstream, partial restriction restricts pump throughflow at anything over 1000revs. Would that be enough to create the symptoms observed on the pump itself?
Click to expand...

Yes, it would do exactly that. Positive displacement pump discharges cannot be throttled. In theory the discharge pressure will increase until either the pump casing or the pipework bursts, except in plant there is always a PRV. Where so much of the installation is rubber I would expect the vanes to be driven harder and harder against the casing, which with the reduced water flow would result in temperature increase.

In this case I would be looking at the heat exchanger tubes, already mentioned, and the hoses between it and the pump.
 
I was kind of hoping you would be along Vic, ta

This sort of experience/stuff is IMO always worth carrying around as part of the skippers cerebral toolbox

There was a great thread on here couple of years ago about overheating and poor self priming that culminated in the discovery that the pump cam had worn down to a shadow of its former self ( silty French canals IIRc).. So obvious once you 'see' it of course, and the OP kindly posted it all thru to a happy conclusion..
 
Thanks for all these replies.

This morning we took the gear oil cooler off - lots of weed and the stack tubes were full of crud. Cleaned and acid washed, then restarted - still steaming! But now there were drips from the gear oil cooler flange and when we tightened it up the flange snapped. Maybe air in the vacuum side was reducing water flow?

West's are soldering that back on. From Vyv's and BB's posts I understand now the effect of back pressure.

Other posts suggested checking muffler and exhaust hose - now done. Engine oil cooler stack checked and no restrictions.

Please keep posting with ideas and questions and we'll get to the bottom of this.

Simon
 
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 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
Click to expand...


Seems to be a catalogue of fun and games concerning the Sea Water system! It is unlikely the engine suffered if your observations regarding the temperatures is correct.

The cut away would appear to be a gap between the sea water pump itself and the bearing transmission section and the red hot disc may be the water throwing disc which is there to stop leakage water entering the bearing chamber. If this thrower was rubbing adjacent housings it may suggest that the bearings are worn so the pump should be inspected both at the water end and the bearing housing end. As others have said you should check the impeller. cam , housing and end cover for wear. Also check the bearings and seals and ensure the shaft is correctly located in the correct running position.
 
Thanks for that. Impeller out this afternoon and we'll inspect the cam, my suspicions are that it's worn down, I'll compare it with the measurements for the worn one on Vyv's site, not the same but may be proportionate.
 
Lazy Kipper said:
Thanks for that. Impeller out this afternoon and we'll inspect the cam, my suspicions are that it's worn down, I'll compare it with the measurements for the worn one on Vyv's site, not the same but may be proportionate.
Click to expand...

Many of the larger pumps come with a replaceable cam, usually part of the full refurb kit. You can identify it by the retaining screw passing through the body from outside.
 
vyv_cox said:
Many of the larger pumps come with a replaceable cam, usually part of the full refurb kit. You can identify it by the retaining screw passing through the body from outside.
Click to expand...

The spares kits often come with replacement back plate which can be removed and replaced when the cam is removed. Following a similar problem to yours, after advice from the forum, I carried out a rebuild of my jabsco raw water pump with new bearings, shaft, seal, backplate etc , all with minimal hassle

Hope you get this all sorted soon.
 
I still find the red hot bit very strange.It requires further investigation before thinking about replacing the camplate or backplate.The whole pump must be taken to bits and checked.Things don't go red hot without something being very wrong indeed.
 
Update:

The gearbox oil cooler had an air leak on a collapsing collar, this is on the negative pressure side so air was easily drawn in. A whole day of pulling and pushing and a new oil cooler was in - SWMBO was a trooper, hanging into the bilges tightening oil pipes. At 80% revs we have a third of the steam we used to, but still a little. I think the Jabsco pump is worn and needs a winter rebuild.

Thanks to everyone who contributed, PBO's finest.
 
You must log in or register to reply here.

Other threads that may be of interest

ianc1200
Sureseal shaft seal.
2
Replies
20
Views
483
ianc1200
ianc1200

Share this page

Top