Overheating Kubota - I Need Advice

[mobetah]

Thanks Chief,

I haven't but I will as soon as I get back to the boat. The engine and exhaust elbow are basicly new (about 400 hours). I wouln't think that there would be scale or be corroded but that doen't mean that something (as in impeller blades or trash) may not be lodged there. I'll measure the flow out the exhaust then take everything apart, make sure it's clear and clean then measure how much water is flowing from the pump, through the heat exchanger, and out the exhaust.

Thanks again, Bill A.

[Chief Engineer]

Don't just measure the flow out the exhaust.

Take the hose off where it goes into the elbow. Put it in a bucket (5 gallon)and observe the rate of flow. 18 GPM should fill it in 20 seconds or so.

You should be able to run the engine w/o cooling water to the exhaust for that short of a period

[Alan Wheeler]

I had already suggested he check that chief, but it seems he already has his mind made up.
However, if he would take the time to listen to some other suggestions.
I think there are other issues here.
How is 2800RPM max. Is that the max RPM you can get from your engine in gear?? or are you saying that 2800RPM is the max rated RPM for that engine. Because it should rev much higher than that. If you can not achieve max RPM, then you are overloading the engine and that wil cause overheating. If you can not even maintain 2400RPM, you are very much waay over proped and that needs to be corrected first before you look at any other part of your system.

[Boracay]

Unless the thru hull is known to be totally clear I would put a small amount of money (given good odds) on the thru hull (or the valve) being partially blocked.

It does not take much to block a 3/4" hose.

Have you considered upgrading to a 1" thru hull with 1" hose right through to the raw water pump?

It may be possible to disconnect the raw water hose, hold it above the waterline and poke something flexible down to make sure the passage is clear.

The John Deere on Boracay is rated at 75hp continuous, has a 1 1/4" inlet to the water pump and a 1 1/2" sea water inlet.

When we slipped last time the cover over the raw water inlet was partially blocked.

[Alan Wheeler]

Thats a big plumbing size for Hp Boracay. Nothing wrong with that of course.
I have a perkins 6.354 and it is only 1". But I too have an 1.75" through hull and seacock to the intake filter and then it's 1" on through from there. My intake filter sits on top of the seacock and the clear plastic lid on top allows me to look straight down to see if the passage way is clear.

[mobetah]

Thanks again Chief and Boracay,

I'll check the exhaust as is, then I'll take the hoses off and check after the pump, then after heat exchanger, then at the mixing elbow and then finally at the exhaust again. That should tell me if the line is being blocked somewhere .... right?

I'd rather not change the size of the thru-hull, seacock, strainer and hoses if not absolutely required. The folks at Oberdorper (pump manufacturer) insist that the 3/4" hose etc. is adaquate for the flow of their m302 pump so perhaps the problem is down stream of the pump ..... if the flow is constricted in, say, the heat exchanger itself then would a larger thru-hull, seacock, strainer, hose etc. in the input line help solve the problem? If the heat exchanger is too small and is manufactured in such a way that will allow a low flow, say 12 gpm, wouldn't increasing the capacity of the heat exchanger and possibly going back to the smaller raw water pump (if a second shell and tube heat exchanger is added in line rater than installing a complete new heat exchanger) solve the problem? Checking the flows as Chief suggests should tell me a lot about what's going on.

Thanks again, Bill A.

[donradcliffe]

2800 is the max rated rpm for that engine--nice and slow and strong.

If the thru-hull and inlet to the pump is 3/4", that seems too small for 50hp. If the flow test shows low flow, you might try to borrow a length of 1" hose and run it from the pump to a bigger thru-hull and see if that solves the problem.

[Alan Wheeler]

Being 50Hp, I am asuming it is a 4cyl. engine. Wow that is indeed a very slow RPM for a 50Hp 4cyl(if it is 4cyl) engine. It should last a very long time at that rate and I bet she is a sweet sounding little honey ticking away.
Bil, the answer to knowing what the next question to look for is in the fact that the blades are failing on the impellor. This is usually caused by an intake restriction. Output restriction should not be ruled out, but these pump can usually handle pressure, they simply can not handle too much suction. So intake restriction or the plumbing before the pump is the best place to start looking. Certainly check the output and as I said way earlier, check that the pipe that marries the hose to the exhaust is large enough. It needs to be 3/4 also.
As foe the old system, going back to the smaller pump and increasing the exchanger size could work. However, the only way of knowing that is to do a temp differential measurement. That's the difference between the seawater temp going in and the seawater temp coming out. Problem is, to be really accurate, you have to also plot the engine cooling side of hot going in against slightly cooler coming out. The difference in both give you a cooling value. If the seawater coming out is very hot, you could say that the water volume is not great enough. So adding another heat exchanger would not solve the issue. If the sea water was coming out too cold, then the issue would be that the cold is not in contact with enough of the hot for long enough. Then you could simply add a larger or another cooler.
Does this installation have an oil cooler?? If not, that could solve a lot of the issue. 40% of the heat your engine develops is taken away by the oil. If you cool the oil, it can dramaticly help with cooling the engine. Good quality oil also helps both in wicking away that heat and reducing friction enough to lower the temp somewhat.

[MidLandOne]

Some other stabs in the dark -

Is there a problem on the coolant side eg thermostat not opening, does it overheat with the thermostat taken out? Doesn't explain the vanes coming off the pump impellor but maybe you introduced that problem with the new pump, so a different deal.

If exhaust exit raw water flow doesn't measure up, a possibility is a delamination in any exhaust hose used restricting flow. Have definitely come across this before. Again, by itself does not explain the pump impellor vanes losses.

The vanes coming off the impellor would seem to me to be a suction side problem - 3/4" seems smaller than what I have normally seen on a 50hp engine, not that I have ever taken much notice of others but our own 50hp engine (also around 2800 rpm max ) all the suction side is over 1 inch, don't recall exact size and don't know the flow but strainer is definitely 1-1/2 inch.

A very, very long shot as is unlikely and would probably seriously disrupt raw water flow to the pump to the extent was very obvious - but is any anti-siphon loop in the raw water incorrectly placed on the suction side of the pump ?

So a possibility to consider when looking for the problem(s) - you had an overheating problem, you installed a bigger pump and introduced a new problem unrelated to the overheating - so now you have an overheating problem and also a pump problem.

[sildene]

Originally Posted by Alan Wheeler

Does this installation have an oil cooler?? If not, that could solve a lot of the issue. 40% of the heat your engine develops is taken away by the oil. If you cool the oil, it can dramaticly help with cooling the engine. Good quality oil also helps both in wicking away that heat and reducing friction enough to lower the temp somewhat.

Useful info in your post, Alan. Question on the oil cooling tangent: If a diesel engine comes with an oil cooler, and we are considering plumbing routes between seacock, oil cooler and heat exchanger, it sounds like you would favour going from seacock to oil cooler first. As opposed to going to the heat exchanger and then the oil cooler (so, getting more efficient oil cooling rather than coolant cooling)?

Martin

[never monday]

Look into the heat exchanger used on the Universal M50

[Brian Russell]

Hi Mobetah,
I was wondering what resolution you came to on the overheating problem with the Kubota 50 from Phasor? This is the same engine I have specified for the Dix43PH I am building, so I got a bit worried reading it. My experience w/ Kubota in general has been great...

Cheers
Brian

[EBCAU]

After reading this thread I thought back to my similar past overheating problems with my 80 hp Lehman Ford.
No amount of physical cleaning of heat exchanger etc., helped with this. Somebody suggested flushing the cooling system with Spirits of Salts (HCL). I mixed about 1 litre with five of water, fed it in via the raw water strainer, and let it stand for about 45 minutes. The resultant discharge on restart was filthy, the copper exhaust outlet looked like new, and the flow estimated to have increased by 20%. The engine has operated perfectly since. It seemed such a simple and effective cure.

Nobody else has suggested this remedy. Has anybody else done this or is there a very good reason that you shouldn't?

[s/v Jedi]

Originally Posted by EBCAU

Somebody suggested flushing the cooling system with Spirits of Salts (HCL).

Wow, that's an old name for it ;-) I did hear it being called muriatic acid before. The name for this today is Hydrochloric Acid.

It is used often to clean heat exchangers and other coolant passages. If at all possible, it's best to re-circulate it. This is easiest done with a bucket and miniature submersible Rule bilge-pump. Pump in the bucket with HCl solution, it's output hose onto the heat exchanger and a hose from the heat exchanger output back into the bucket.

cheers,
Nick.

[EBCAU]

Thanks Jedi,
It is still actually sold under the old name at the local DYI outlet. You have to read the label to know that it's HCL!
I'm happy that so far I am not inundated with replies telling me that this is a bad and damaging practice.
Your method of application is probably more involved but also perhaps more enviro friendly than discharging via the exhaust.