Engine Overheat

[WayneS]

I am somewhat concerned that our brand new Beta 20Hp engine that we fitted last winter seems to overheat.

Yesterday, on three occasions the alarm went off. The first time was when we were punching the big tide out of Portsmouth so that the throttle at the stop. 20 min after starting the engine and 10 min after pushing it to the stop, the alarm went off. I checked water flow and it was there. How good it was out of the exhaust is diff to say as the exhaust is just below water line when under way. However, I could see water flow in the Vetus strainer.

The pipes from the exchanger to the exhaust, which go via an anti siphon device about 1m away, did not feel hot, in fact they were only mildly warm.

After having the engine off for about 5 min things were OK again.

On my return to port I ran the engine at full throttle again and it alarmed once more.

I have an oil cooler between the strainer and the pump but that should give little resistance.

We are over propped so even at full throttle we only turn 3100 - 3200 RPM.

I have since checked the inlet and it is clear, impeller still looks good, so I am confounded.

Has anyone got any wild ideas?

Cheers

Wayne


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[Talulah]

I don't know the 20hp version but is it freshwater cooled? If so did you check the freshwater level?

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[WayneS]

Sorry, should have put that in. Yes it is indirect cooled and the level is OK.

We are doing our 50 hrs service next w/e so am thinking of opening the exchanger to see if it is clear.

Wayne


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[Talbot]

Ifyou are overproped, that will cause the engine to heat up on full throttle - what revs should you get for flat out? If you are more than 500 revs off the supposed top, then you need to change your prop.

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[freebird1]

My dad bought a new Beta 20 and had the same problems. Beta supplied various new bits which he fitted and this cured it. The main one was the heat exchanger. Beta thought that imperfections in the casting could have come adrift and be blocking the water canals.

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[WayneS]

Hi Mark

Engine max is 3600 but I am hydraulic drive and the pump has a max of 3000.

We hit hull speed at about 2700.

Pushed to the stop she will rev to about 3100.

I think I am going to hop on down to Gosport later this morning and run up and down the harbour for a few hours at hull speed and see if she is OK with that.

Wayne




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[cya]

Wayne
I also have a newly fitted Beta 20, recently whilst punching hard against the tide and wind under Kessock Bridge my overheat alarm also came on. I could find nothing wrong, the seawater flow was fine, I had a full freshwater system( I have an expasion tank fitted) and everything else appeared normal. 20 minutes later I restarted with all the covers (compartment) off and it behaved faultlessly ! and has continued to do so ever since. I have not had occasion to push her that hard since so I do not know if the prob is still there?

Luv
Cy

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[Talbot]

in bad weather you will frequently need more power to achieve same speed, so I would not be satisfied with only being able to use 75%.

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[brianhumber]

Practical - Is the heat exchanger clean, heat transfer is affected due to mud, weed or growth (Here at Chi Marina we have had an attack of the white worms)

Theory - If you are not getting full revs on full power then engine will try to overpower itself. If the Heat exchangers are matched exactly to the duty then any fouling or running overfuelled will cause overheating.

You say your discharge flow is cool so in your case I would think its best to have a look see in the exchanger before worrying about matching props to torque etc.

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[chippie]

I think a phone call to Beta could be a good idea. They get good reports for their customer service.

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[jleaworthy]

Agree with Talbot. I had overheating problems finally cured by getting the pitch on my propellor reduced from 14" to 12". The engine revs then increased at maximum from 2700 to 3300 with the boat going faster and, surprisingly, with appreciably reduced fuel consumption. Over propping an engine is bad news, just like leaving a car to struggle in too high a gear.

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[WayneS]

Thanks everyone for your help.

I ran again today at 2700 RPM and the alarm went off. I then removed the heat exchanger and found it to be very blocked. Approx 30% of the tubes were restricted with a sticky goo. Cleaned them out and after driving the boat hard at max revs for an hour I have to believe that the problem is solved.

I can only assume that the oil cooler that I have inline with the raw water inlet was not 100% clean before fitting and has caused the deposits.

Again, great support from Beta who were ready to have someone come and have a look at the engine.


Thanks again to all.

Wayne

BTW, we will seriously consider a re-prop.


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