Overheating 1.8 BMC

[lpp2]

Good Evening

I'm sure this is a familiar topic to all of you judging the number of posts on the same subject! The story so far Engine send out steam from the exhaust after around 15 minutes, temp gauge at around halfway between blue and red if anything slightly more towards the red. Action taken so far tried 2 types of thermostat one with a slightly higher set point for engines that dont heat water for domestic use, ran with no thermostat, put thermostat back, changed the impeller on the jabsco pump, cleaned out the Bowman heat exchanger, found nothing radical inside it.. my cooling system is a raw water system, water is brought into the boat via a strainer through a bowman heat exchanger then shot out the back via the exhaust. The strainer is clear of any debris as is the intake. This is driving me nuts any help would be so gratefully received

regards lpp2

[Stilllearning]

Hi.

Is it possible that air is getting in to the intake side of the cooling, so losing the low pressure needed to keep water flowing?

Years ago a vetus system on a brumtug used to not perfectly seal after a clean out of the filter, so stopping water flow through the system.

[Geoff Taylor]

Hi, A long shot,but is the drive to the jabsco impeller intact and spinning it ok?.

Edited December 12, 2013 by Geoff Taylor

[lpp2]

It seems to be sealed if not the water would just run out and water is going through the system. lpp2

Drive seems ok on the impeller been no loss of flow of water which I would expect if the drive had packed up. lpp2

[RLWP]

Apart from the steam, why do you think it is overheating?

 

The steam out of the exhaust is from the raw water part of the system, of course

 

Richard

[alan_fincher]

A long shot, but a forum member with a raw water cooled BMC 1800 had a lot of trouble with overheating, even though the water appeared to be flowing sufficiently.

 

One professional engineer had failed to diagnose it, but fortunately he engaged another that was spot on.

 

In that case, (from memory!), part of the "suction" side of the raw water cooling used some copper pipes with soldered joints, and one of these had enough of a leak in it that air was being sucked in, greatly reducing flow through the system.

 

Once soldered up again, far more canal water got sucked through, and the problem was completely solved, I think.

 

So, I would suggest it is worth seeing if as much water is being thrown out of the exhaust as actually should be.

 

It' quite probably not this - but at least a possibility to eliminate.

 

Also, if any of the "openable" parts of your strainer might have a small air leak, that could of course also have similar results.

[Tony Brooks]

There may be nothing wrong with it at this time of year. Some of the water being injected into the exhaust on a wet exhaust boat will boil and then condense back to water as it passes down the exhaust. There will be warm water vapour left in the exhaust flow that can look like steam on cold days.

 

You can not rule out air leaks on the suction side of the raw water pump simply because it pumps an does not leak water. A slight air leak under suction will just reduce the water flow and exacerbate the above.

 

The raw water pump will wear over time and that can also allow air to be drawn into the system or reduce the pump's capacity. If any seals in the body wear or if its a "shaft in body" type bearing wear may allow air to leak in. If the front cover or the back of the pumping chamber grooves by the cam it will reduce pump output.

 

Most 1.5s used a belt driven raw water pump, is the belt tight enough?

 

Personally I find talking about red and blue sectors on a temperature gauge far from helpful. We really need actual temperatures (infra red thermometer on the thermostat housing? That temperature could be normal unless it keeps creeping up and into the red.

 

A scaled up exhaust mixing elbow or a de-laminating exhaust hose can both increase the exhaust back pressure , thereby reducing the pump output and making exhaust steam more likely.

 

Just noticed its a 1.8 and the timing cover makes a camshaft driven pump more likely but it may be belt driven.

Edited December 12, 2013 by Tony Brooks

[lpp2]

Just followed the pipework from the strainer to the pump and found a length of around 6 inches long of what looks like blue drinking water pipe pushed into the black heater type hose and held by jubilee clips, could this be the cause regards lpp2

Yes tony its belt driven lpp2

[koukouvagia]

A long shot, but a forum member with a raw water cooled BMC 1800 had a lot of trouble with overheating, even though the water appeared to be flowing sufficiently.

 

One professional engineer had failed to diagnose it, but fortunately he engaged another that was spot on.

 

In that case, (from memory!), part of the "suction" side of the raw water cooling used some copper pipes with soldered joints, and one of these had enough of a leak in it that air was being sucked in, greatly reducing flow through the system.

 

Once soldered up again, far more canal water got sucked through, and the problem was completely solved, I think.

 

Yep that was me. I had exactly your symptoms. The dry joint which allowed air into the suction side of the cooling circuit was replaced by a compression fitting and the problem was solved. I would never have found the cause myself. Three cheers for local engineer, Ed Boden.

[lpp2]

This might sound a daft question, just because a joint is water tight, that is no guarantee that it's also airtight, is that right, because if it is I'll replace the hose tomorrow. lpp2

[MtB]

This might sound a daft question, just because a joint is water tight, that is no guarantee that it's also airtight, is that right, because if it is I'll replace the hose tomorrow. lpp2

 

How do you know it is watertight if it is above the waterline?

 

Another question not yet asked or covered... What is the history of this problem? Did it start suddenly one day? Or develop slowly over a period of time? Did it ever run cool? Or have you just bought the boat?

 

MtB

[lpp2]

The problem has been coming on slowly for around a month or so. As for the watertight question i was refering to the joint in the pipework what lm asking is because this joint isn't leaking water could it be leaking air. Think I've put that right. lpp2

[ravenspell]

One thing to check for is that the cooling water intake under the boat is not blocked .Easiest way to check this to remove the inlet pipe where it connects to the water pump and simply blow down the pipe..If you cant blow bubbles or meet strong resistance then there could be a blockage under your boat.

[Tony Brooks]

The problem has been coming on slowly for around a month or so. As for the watertight question i was refering to the joint in the pipework what lm asking is because this joint isn't leaking water could it be leaking air. Think I've put that right. lpp2

 

Yes it could, especially on the suction side.

[lpp2]

Good evening

after a very long night last night I think I've made some progress. I took the pipework apart where the water enters the boat and cleaned it, i then replaced all the pipework from the strainer to the jabsco pump, then replaced the belt driving the pump and tensioned it properly. Straight away when I started the engine it was obvious by looking at the strainer that the water was coming into the boat with much more vigour. I had a two hour cruise around lunchtime and im very happy with the result, but just bloody annoyed at myself for not checking the obvious first, thanks for everybodys help and comments.

Regards lpp2