Beta marine 20hp - overheating ideas please

[Oldgeezer]

A bit of history as it might be relevant.
The engine is 4 years old - 120 hrs on the clock - no previous history of overheating -
Until last year when the boat was taken out by my son who didn't notice no cooling water coming from the exhaust.
The engine overheated a few times and destroyed the impeller and exhaust waterlock etc.
So end of last season, new waterlock, impeller, remnants of antifreeze drained and replaced.
It ran with no problems for a dozen hours or so before lay up.

This year, I drained the anti freeze again and put in fresh.
I cleaned out the heat exchanger (not much in it anyway)
Last week I had gone approx 1hr when the overheat alarm sounded
~Got towed back to mooring and started engine.
After 30 seconds the alarm went off.
The boatyard then installed a new thermostat thinking it probably wasn't working.
I also checked the heat exchanger was clean.

This morning the alarm went of after 20mins running on my mooring! Engine cover off so no ambient heat.
There is lots of raw water coming from the exhaust (I measured in a bucket) It wasn't warm but then I'm not sure it should be.
The heat exchanger felt cool
The thermostat housing was hot
The flexible hose that connects to the bottom of the fresh water pump was cold (is that right?)
I can only think it may be the fresh water pump - but these are very reliable (or are they)

I will contact beta tomorrow but I'm running out of ideas.
Do you have any?
Thanks
Keith

 

[cryan]

Do you have an accurate thermometer or are you just going on the alarm? If so you may have a dodgy alarm. It is not uncommon for thermocouples to play up after they have been roasted. Can you squeeze the pump hoses ? If you can there is probably no flow or at least you should feel flow. Never mind the teperature of the cooler, you want to see if there is a temperature difference between the inlet and outlet. I'm surprised that the boat yard changed the thermostat on a suspicion as it can be easily tested in a saucepan of boiling water which would tell you for sure. If you can find or borrow a laser thermometer it will be very simple to see if the engine is running fine and the cooling system working. If that is the case the sensor is knackered.

 

[vyv_cox]

I think your diagnosis is correct. Clearly no circulation. Could be the pump impeller, but could also be a blockage, maybe the thermostat for a second time? I would try running without the thermostat, see if the hose and heat exchanger warm up. You can check thermostats easily in a pan of water on the stove. I am assuming you are sure there are no airlocks.

Unfortunately, and maybe following on from the abuse the engine suffered, cracks in the head can also disrupt circulation. But check the easy things first.

 

[Oldgeezer]

I'm not entirely sure there are no airlocks - but dont know how to check?

I think a thermometer is a good idea - at least I'll then know what is properly hot and what not!

PLease not a crack in the head!

A few more things to look at anyway
Thanks

 

[Oldgeezer]

I now have a new temperature sensor but not sure where it goes.
I assume its a simple disconnect the wire, unbolt the old and pop in the new one.

Can someone point me in the right direction to find its location on the engine?

Many thanks

 

[Habebty]

Go to the beta website and download the manual for the BD722, I assume.
Check antifreeze mixture is correct and raw water inlet is not partially blocked or inlet suction hose is not collapsing under suction. Cure for my Beta problem was larger dia. raw water skin fitting. Clean out thermostat housing and surrounding pipe with bendy wire.

 

[lenseman]

I now have a new temperature sensor but not sure where it goes.
I assume its a simple disconnect the wire, unbolt the old and pop in the new one.

Can someone point me in the right direction to find its location on the engine?

Many thanks

Go to the back of the temperature gauge on your boat and look at the wiring on the back of the temperature gauge.

Discount any wiring that is used for illumination and note the colour code of the wire which goes into the back of the gauge from the engine sensor. It could possibly be Green with a Black trace or white with a green trace or something similar.

Now look on your engine and near the top and close to the thermostat / water pump area you should find a similar coloured wire. Follow it to where it is clipped/plugged into the NTC temperature sender unit. In this way, you should be able to make sure you are on the temperature and not any oil sender unit.



.

 

[BabaYaga]

The temp sensor is on top of the engine, to the rear of the injectors, not far from the air filter housing (assuming this has not been changed since the Beta 722, 2005 model)

 

[concentrik]

A bit of history as it might be relevant.

It will be, especially when you find the cause, look back and say 'Ah yes, of course'.....!!

The engine is 4 years old - 120 hrs on the clock - no previous history of overheating -

120hrs - I wouldn't have thought that's enough time to build up any significant scale or other deposits

Until last year when the boat was taken out by my son who didn't notice no cooling water coming from the exhaust.

Do you mean "he didn't notice that there was no cooling water..." or " He didn't notice whether there was no cooling water"?

The engine overheated a few times and destroyed the impeller and exhaust waterlock etc.

Probably the first then?

So end of last season, new waterlock, impeller, remnants of antifreeze drained and replaced.

Remnants? Was there very little secondary cooling water?

It ran with no problems for a dozen hours or so before lay up.

Thinking about events so far, then: At some point there was no cooling water emerging from the exhaust. So there was a problem with the raw water (primary) flow. You say the engine overheated a few times and destroyed the impellor.... can I suggest that it was the other way round? That the impellor shredded, the primary circuit failed so there was no cooling available to the engine, which then overheated and damaged the waterlock (V.hot exhaust as no elbow cooling). You then replaced the impellor, secondary water/antifreeze and the engine operated correctly for 12 hours. It appeared to be ok. So what happened between then and this:

This year, I drained the anti freeze again and put in fresh.
I cleaned out the heat exchanger (not much in it anyway)
Last week I had gone approx 1hr when the overheat alarm sounded

~Got towed back to mooring and started engine.
After 30 seconds the alarm went off.
The boatyard then installed a new thermostat thinking it probably wasn't working.
I also checked the heat exchanger was clean.

A thermostat failure could account for the problem but assuming it was working and fitted correctly you have eliminated that.
I think the heat exchanger is a dead end. The fault occurs at idle (when less heat needs to be dumped) and it would need to be very blocked to be unable to transfer a small amount of heat. You've cleaned it once (I assume you didn't find loads of constrictng sediment/rust/crisp packets) so it should be fine.



This morning the alarm went of after 20mins running on my mooring! Engine cover off so no ambient heat.
There is lots of raw water coming from the exhaust (I measured in a bucket) It wasn't warm but then I'm not sure it should be.

You have plenty of raw water from the exhaust - but it isn't warm. This needs more checking I think. There should be a marked difference between the in and out water. After all, this (apart from background air cooling and exhaust gases) is where the engine heat goes.

The heat exchanger felt cool
The thermostat housing was hot
The flexible hose that connects to the bottom of the fresh water pump was cold (is that right?)
I can only think it may be the fresh water pump - but these are very reliable (or are they)

The heat exchanger won't be very hot usually - the raw water flow is taking the heat away. But cool...? And the thermostat housing hot...? It would probably be worth verifying the secondary water circulation now. Reliable or not, everything can fail.

I don't know how helpful Beta Marine are to end users but it might be worth emailing them. They could give you some 'empirical' tests which don't rely on instrumentation.

Sorry if others have posted already - it takes me ages to type this stuff!

 

[Oldgeezer]

Wow - What excellent help!
Many thanks to all.

Concentrik - your analysis looks spot on. The initial cause was raw water intake blocked.
Will try the new temperature sender today and taking an infrared thermometer with me too.
I do recall when emptying the fresh water the drainage tap was blocked and I had to poke it with a stick!
Perhaps something was dislodged.
I'll report back later today - hopefully the sender was faulty. but...

Again, many thanks to all.

 

[Pye_End]

I have a vague memory of a Bea thread where somebody changed the coolant water but was having overheating difficulties afterwards. Sounded as though there might have been an air lock which cleared. Can't find it now.

 

[boatmike]

One obvious thing I am surprised no one has mentioned is that often if you have an impellor failure (which you have had) bits break off the impeller and create a partial or intermittent blockage downstream of the pump. Its pretty easy to see the flow of water (or lack of it) by looking at the exhaust outlet at tick over. There should be a copious flow coming out as you suggest there is. If there is you might think there is nothing wrong with the coolant flow. NOT SO!! I have several times seen a bit of impellor caught in an elbow or union which passes water when at tick over but when underway and the pump rate increases shuts off the supply. See if you can check the coolant flow at high revs. If it is OK disregard this post. If it ain't..... take the pipes off and check thoroughly that there is no intermittent blockage...

 

[NealB]

One obvious thing I am surprised no one has mentioned is that often if you have an impellor failure (which you have had) bits break off the impeller and create a blockage downstream of the pump. Its pretty easy to see the flow of water (or lack of it) by looking at the exhaust outlet. There should be a copious flow coming out. If there is there is nothing wrong with the coolant flow. If there isn't you possibly have a bit of old impellor stuck somewhere downstream of the pump.

I thought that, too.

The only thing I'd add is: don't assume that broken impellor vanes will always go 'downstream'. With our old BMC Commander, several bits of vane were found upstream.....yes, I'm being perfectly serious!

 

[concentrik]

Impellor debris can certainly cause obstruction in the narrowest parts of the water path; it caused me a great deal of trouble and a lot of time spent faultfinding. After locating the constricted area and removing rubber, steel grub screw (x2) and bits of string the unobstructed water flow returned to what I can only describe as torrential.

But the OP said
This morning the alarm went of after 20mins running on my mooring! Engine cover off so no ambient heat.
There is lots of raw water coming from the exhaust (I measured in a bucket)

So it took only 20 mins to boil, even though there was 'lots' of raw water coolant emerging. About 20 mins is about the time I would expect an idling (was it?) engine to heat the block and cook its uncirculating secondary circuit. The raw water from the exhaust is not warm - which suggests the engine heat is staying... in the engine. It hasn't melted the exhaust box because there's plenty of raw throughput. All of this suggests to me that the primary circuit is making cold seawater available within the heat exchanger but the secondary circuit is not functioning correctly. I don't know this engine, but would it be possible to disconnect the output hose (if there is one?) from the secondary pump and see if it is pumping with the engine turning on the starter? Perhaps you could run the hose to a bucket so you don't lose the antifreeze!

Temperature measurements are unlikely to be helpful if you don't have any 'known normal' readings to compare to.

 

[PaulMcC]

I'm a novice at this kind of thing (but have a Beta 25 so interested in finding out what the problem is). One thought/question though, how much of the work of moving heat around within the engine is done by the oil? So if you have an oil problem - low level or blockage or whatever - would this cause some parts of teh engine block to get hot even if the cooling water system is working?

 

[concentrik]

I'm a novice at this kind of thing (but have a Beta 25 so interested in finding out what the problem is). One thought/question though, how much of the work of moving heat around within the engine is done by the oil? So if you have an oil problem - low level or blockage or whatever - would this cause some parts of teh engine block to get hot even if the cooling water system is working?

Some, but the heat is produced in the cylinder(s) and to an extent in the cylinder head. Some of this heat is expelled via the hot exhaust gases, some is dissipated to the surrounding air (the engine gets hot!) and yes some is carried by the oil through the oil cooler (if there is one) but the remainder of the heat energy - most - is transferred to the water jackets which surround the cylinder (and head); the water in these jackets and waterways is pumped (by the secondary pump) through the heat exchanger, which transfers the heat to the raw water which is being pumped by the primary, seawater pump. The oil does play a role in spreading waste heat around but is there primarily to reduce friction. OK I'm at the limits of my knowledge now, so I'll hunker down....

 

[davidfox]

Have you cleared the oil cooler, im not an expert, far from it, but the impellor bits went and blocked my oil cooler and the engine overheated Sound feasible?

 

[mtb]

why not get the engines coolant tested to see if there's a head gasket or head gone, it is a simple test to see if exhaust gases are present.
I would think any garage would have the testing kit

cheers
mick

 

[LittleSister]

So it took only 20 mins to boil, even though there was 'lots' of raw water coolant emerging. About 20 mins is about the time I would expect an idling (was it?) engine to heat the block and cook its uncirculating secondary circuit. The raw water from the exhaust is not warm - which suggests the engine heat is staying... in the engine. It hasn't melted the exhaust box because there's plenty of raw throughput. All of this suggests to me that the primary circuit is making cold seawater available within the heat exchanger but the secondary circuit is not functioning correctly. I don't know this engine, but would it be possible to disconnect the output hose (if there is one?) from the secondary pump and see if it is pumping with the engine turning on the starter? Perhaps you could run the hose to a bucket so you don't lose the antifreeze!

+1

My money's on a problem with the freshwater (anti-freeze) side of the system, quite likely (but not necessarily!) a result of damage caused when the seawater side of the sytem was blocked.

 

[Oldgeezer]

And the answer is....

The temperature switch (sender) was faulty!
I contacted beta marine and they suggested it - as did a previous poster here.

I had already cleared the heat exchanger of any impeller bits / anode bits etc. There wasn't much in it but I poked through all of the tubes anyway.
Apparently, the raw water doesn't get particularly warm coming out the exhaust as there is so much of it (a couple of degrees that I couldn't feel)
The boatyard had suspected the fresh water circulation and had changed the thermostat (I now have a spare).
Next suspect would have been the fresh water pump (which never fails!) but fortunately problem solved.
Dont think the engine has an oil cooler.

Thanks to all for advice and suggestions. Used it today against a strong northerly for a couple of hours - no problems.