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Old 06-06-2008, 06:42   #1
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Overheating Kubota - I Need Advice

Now that the new fuel and water tanks are in it's time to tackle the overheating Kubota.

Background:
I have a 50hp kubota marineized by Phasor. At higher RPMs, the engine has ran hot from day one. I have been told (by Phasor's competition) that Phasor's heat exchanger is inadaquate on the 50hp engine (the heat exchnager tube stack is 2 inches by about 15 inches). After discussions (arguments ?) with Phasor, they agreed to fix the problem .... They did not however replace the heat exchanger .....what they did was furnish a large new water pump">raw water pump ( Oberdorper M302 09) which was mounted behind the injector pump (not on the front of the engine)(while they furnished the pump, it cost me about $500 for labor, misc. parts and travel for their dealer to install it). I'll admit, the new pump cools the engine for a while however, after a few hours of use the impeller blades start to break down and the engine temp starts to go up again until the impeller completly fails the temp goes off the chart. Motoring from Pensacola FL up the Tenn-Tom waterway to Demopolis AL (about 55 hours run time), I had to replace two impellers. I have been unable to obtain a flow chart on the M302 pump but Oberdorper's other 302 pumps appear to have a flow rate of about 29 gallons per minute at 2800 RPMs (the Kubota's max RPM). The raw water hoses, strainer, ports on the pump and ports on the heat exchanger are all 3/4 inch.

Questions:
1. Since the existing heat exchanger is new and would be expensive to replace with a larger heat exchnager from one of Phasor's competitors (are their heat exchangers really larger than Phasor's?), does anyone see a problem with installing a second shell and tube heat exchanger (2" x 15") in series with the existing heat exchanger? If it cools the engine it would be MUCH cheaper less expensive since I already have an additional heat exchanger in my garage.
2. I'm going to call Depco Pump today in order to get more information and/or recommendations concerning the M302 09 pump. Does anyone have any recommendations for a pump which would fit the front of the 50 hp Kubota and be adaquate to cool the engine (using two 2" x 15" heat exchangers). I'm not sure what pumps Beta, Nannie or Frontier ( all marine engines built on the Kubota 50 hp) use.

Any information, advice or recommendations would be greatly appreciated.

Thanks, Bill A.
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Old 06-06-2008, 08:05   #2
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I have a new Beta 50hp, which uses the Kubota 2203 engine. It has a lot of reserve cooling capacity. The heat exchanger is about 2 1/2" x 15", but is built into a complex (read expensive) casting which also includes the exhaust manifold. The Beta uses a Jabsco 29500-1501 raw water pump, rated at 9 gpm at 1500 rpm.

http://www.jabsco.com/files/section_...r_pumps_07.pdf recommends 15 gpm raw water flow for every 100 engine hp, so you are looking for 8gpm at wide open throttle. Pump ratings mean nothing unless they are at the pressure differential which matches your system. If your exhaust is out of the water, you can try catching it in a 5 gal bucket to check flow rate.

Now my questions:

1. Did the new pump replace the old raw water pump?

2. How is it powered?

3. Is it upstream or downstream of the heat exchanger? (If downstream, that is why it fails when things heat up)

4. Is the heat exchanger plumbed for counterflow (raw water enters at one end, hot engine water enters at the other end) for maximum efficiency?

Heat exhanger capacity is a function of surface area of the tubesheet, rather than overall size. Before you worry about adding heat exchangers, lets make sure you are getting the raw water flow that you need, and that things are plumbed correctly.
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Old 06-06-2008, 08:19   #3
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Excellent information & advice donradcliffe !
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Old 06-06-2008, 10:35   #4
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Thanks Don,

Yes, the new waterpump which Phasor installed relaced the old Oberdorper pump.

The new pump (as well as old pump) was mechanical powered (NOT belt driven).

The new (as well as old pump) are upstream of the heat exchnager.

I'm not really sure about the counterflow (I not at the boat right now) .....I think the raw water enters at the rear of the heat exchanger and also exits at the rear .... the engine coolant enters near the front ... can't really remember exactly where or how it exits.

There is plenty of flow (I think as much as you can get through a 3/4" hose) I just don't think there is enough for the new large M302 pump. I think the new pump is starving for waterand that is destroying the impellers.

The existing Phasor heat exchanger is also a cast manifold etc., much like yours, that would be expensive to replace.

The tube stack has (if I remember correctly) 22 tubes which are about .22 inches in diameter.

Thanks for your help,
Bill A.
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Old 06-06-2008, 16:52   #5
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Downstream?

So your rubber impeller pump is after the heat exchanger?
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Old 06-06-2008, 16:59   #6
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Boracay,

No, the pump is upstream from the heat exchanger .it pumps water downstream to the heat exchanger.

Thanks, Bill A.
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Old 12-06-2008, 02:59   #7
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When you say "over heats" what temp is it reaching??
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Old 12-06-2008, 17:42   #8
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Is there a water heater plumbed into the engine?

Is there a possibility of an airlock?

Just more to chew on.
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Old 12-06-2008, 20:28   #9
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Prior to installation of the large raw water pump .... at near maximum RPMs (2400/2800) the temp would rapidly reach 210 degrees F (or more if you let the engine run at that speed - I would shut it down or lower the RPMs)

There is now a water heater plumbed into the system however, I have already disconnected (eliminated the water heater) from the system and it overheated just the same.

Airlock? I really don't think so..... As stated above, I have eliminated the water heater and external hoses, etc. (eliminating any hoses etc. where there might be an airlock) with no change in the overheating problem.

Again, Thanks for the help ........... Bill A.
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Old 13-06-2008, 01:03   #10
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In regards to the old system, If it doesn't continue to climb any higher than 210, what's wrong with that?? You should expect the temp to rise if you push maximum.

For your new pump, you are correct that intake restriction causes blades to break. So I would imagine one of two things. The intake is too small, or restricted by something. Ensure the seacock is not too restricting. Sometimes they can one heck of a small orifice.
The other problem that can restrict water flow when going up a size in pump is that the exhaust mixer is never usually changed and that can often be only 1/2". If you want to blast water in at a high pressure, 1/2" is fine, but for a good flow, it also needs to be 3/4". But if you increase the flow through and the issue is the intake, the blades breaking issue is always going to exist.
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Old 13-06-2008, 06:16   #11
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Intake hose?

Greetings sailors,
I know that this seems obvious, but here we go anyway:
When we purchased our boat the engine ran too hot. The raw water circulating pump didn't pump enough water and needed to be rebuilt. We replaced it instead with a higher capacity pump. Since it was sucking more water at higher suction it sucked the hose between the strainer and the pump shut. So, ironically, with the new pump we still were overheating, for a different reason. Replacing the hose from the throughhull to the pump with hose rated for suction solved the problem. We weren't able to get the appropiate marine hose quickly so we used hydraulic return hose which rated for suction and can be gotten at any hydraulic shop. Its worked great for a couple of years.

To get full flow to the pump I also used 5/8 hose and hose barbs upstream from the pump even thought the rest of the system is plumbed with half inch hose and fittings. This avoids creating a bit of a bottleneck due to the wall thickness of the barbs and may also minimize the impeller blade breakage issue mentioned by Alan.

Paul Meyer
New Brunswick
Canada
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Old 13-06-2008, 07:44   #12
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Alan,
Like I said, the temp would go higher than 210 degrees if I let it (and it has on a couple of ocasions at 2300 or 2400 RPMs, not at the maximum 2800 RPMs).I don't think it would be wise to try and find out exactly how hot the engine would get .... If it would get to 230 degrees, 240 degrees or 250 degrees, I think it's too hot, there is a problem and the problem needs to be fixed. I'm just trying to figure out the best and/or least expensive fix.
Thanks again, Bill A.
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Old 13-06-2008, 14:07   #13
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Hello everyone,

I just talked to the folks at Oberdorper Pump Co. They say the 302m pump should pump about 18 gpm at 2800 RPMs. In addition, they stated that the 3/4" line should provide enough flow to the pump...... finally, they stated that they would look at the pump to see if their is a problem with the pump.

If Jabsco recommends 15 gpm for each 100 hp then it would appear that an 18 gpm for a 50hp is overkill. I think I'll send the pump back to them and make sure that there is nothing wrong with the M302 03 pump however, I think I'll go back to the original M202 17 Which produces approximately 9 gpm at 2800 RPMs and install a second heat exchanger inline with the original Phasor heat exchnager (I still think the size of the original heat exchanger is real problem).

I'll let you know how it turns out, Bill A.
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Old 13-06-2008, 14:41   #14
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Quote:
not at the maximum 2800 RPMs).I don't think it would be wise to try and find out exactly how hot the engine would get
You did not make it clear and I did not say "find out how hot it can get".

It seems you have made up your mind and it also seems your mind was made up from the beginning and you are simply trying to find the answer you want to hear.
Let me say this in a different way. You have an issue with the flow of water through your pump, most likely due to a restriction. That is why your blades are breaking. It is possible the flow is restricted at the outlet end, but normally that does not cause blade failure. Hover, that should not be ruled out. Fitting another heat exchanger will not solve your problem if the problem is not enough cooling water.
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Old 13-06-2008, 18:53   #15
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Have you checked the flow where the water goes into the exhaust elbow?

I just replaced a Ford-Lehman elbow.....the Injection line was corroded/scaled so much that a pencil barely made it thru----read restriction.

The owner said he had never seen water flow like that in the time he owned the vessel following the new installation
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