Overheating Capital Gear Box

[Paulyne J]

I have a Capital Hydraulic Gearbox, this box was recently completely rebuilt and ever since the rebuild it has a bad overheating issue, the rebuilders are suggesting a larger raw water heat exchanger that I am just about to install one but I was wondering if there was someone with any idea why this has started after the rebuild. It will run all day at 6knts but as soon as you step it up the heat come up with it.

Edited June 17, 2013 by Paulyne J

[Testlab]

A few ideas on the cause, assuming it was running ok for years prior to the rebuild.

1. The pump intake screen (filter) is choked up with fuzz from the wear in period. Remove and check, keep checking.

2. The hydraulic hoses are leaking, allowing air into the system and the clutch packs are slipping and getting too hot.

3. The pump has low output and clutch slipping and getting too hot.

4. Heat exchanger has been reverse connected, dumping crud into the tranny and blocking pump/filter.

5. The clutch packs are different to the originals and produce more heat.

6. Incorrect transmission fluid

7. Blocked heat exchanger

8. Shift cables/shuttle valves are not moving all the way - clutch not fully engaged and too hot.

9. Trolling valve jammed or not reconnected properly.

At what load is it getting hot? Cruising above 6 kts or pulling 2 tonnes of nets above 6 kts?

[Paulyne J]

Hi Flathead, Thanks for the thoughts,

The intake filter lines and heat exchanger are all new or reconditioned.

The Hydraulic lines are new.

The box including the pump were reconditioned less than 100 hours ago.

The fluid I changed and went to a far heavier one with no change to the problem.

I like your ideas in general but the 3 below are very possibly the cause.

Clutch packs not the same as the origional

Shift cables/shuttle valves are not moving all the way - clutch not fully engaged and too hot.
Trolling valve jammed or not reconnected properly.

I do not drag nets the boat is for private use, the problem only comes when I start to push above 6knts, the pressure drops and the heat increases to a point that we loose drive. If you stay at 6knts it will go all day. We are doing about 1600rpm at 6, it would be good to have some more speed, before the rebuild we could get 8-9knts easily now we can get it for 10 minutes and we are out of action.

Given your ideas re Clutch Pack, Shift Cable Shuttle Valves or Trolling Valve do you think there any point in increasing the size of the heat exchanger when the problem could be one of the problems that you have highlighted.

Thanks for your help.

[Testlab]

I would have a talk to the reconditioning workshop. If it ran OK before then it shouldn't need a different heat exchanger. Have you had this boat for a while or is it a recent purchase?

Maybe a bigger heat exchanger will solve it but I would be wondering why it is needed. It may be a perfectly normal thing for the type of clutches fitted during rebuild to require a bigger xchngr. Did the rebuild workshop supply the new heat exchangers or were they sourced separately?

To check the lever and valves are moving all the way, take off the shift cable and manually put it in gear and run up to speed and see what happens. If the shift lever isn't moving all the way it may be the cause.

Does it increase temperature rapidly or very slowly? If rapidly the clutches are probably starting to slip, hence the rapid rise once the load gets past the friction limit. If slowly it may be the xchngr is too small.

Lastly.... Do you have a rope around the prop and shaft? Is there enough water passing through the xchngr - maybe the raw water pump impellor is shot and the gearbox xnchngr is last in the chain so it's getting a double whammy of low flow and hot water from the engine cooling system.

Edited June 27, 2013 by Testlab

[Paulyne J]

Hi Flathead

The Guys that built the box do all types of marine boxes, they were not as familiar with the Capital as say a Twin disc but they were confident with the build and have been helpful but not definative with what the cause is. I have had the boat around 12 months. The rebuild was done after four months. It was complete the old box was rebuilt the heat exchanger was sent away by them and reconditioned new hoses and hydraulics no expense spared. They are prepared to supply the new larger exchanger.

When neutral is selected it is hard to maintain, it slips into gear unless you find the exact spot, I will check the range again on the weekend but I am sure that I already have checked the range.

The temperature is a very rapid increase, smell pressure drop and temperature increase all in 2-5min more like 2 though.

I dived on the boat and checked everything and I was able to turn the large shaft and prop in neutral. The PSS seal and the keel shoe re shaft and alignment was done at the same time as the box.

The water flow is separate to any other cooler on the boat with its own pump and flow out of the side of the wheelhouse, I am sure there is no blockage to the intake.

Thanks for your suggestions, it is very helpful to hear your perspective. I feel the clutches are slipping after reading what you have suggested.

What do you think?

I am thinking to have the valve rebuilt or replaced with a new one given the neutural issue / the possibility this is the cause and while that is being done I will plumb in the new heat exchanger.

Thanks so much for your advise.

The problem has been troubling given the lack of confidence in heading deep sea after I have done so much work to make sure that the boat was bullet proof.

Many thanks great advice.

[Testlab]

Good luck. These sorts of things can be really annoying but certainly don't head to sea without being 100% confident. It's does sound like slipping to me. I am more familiar with Twin Disc and ZF boxes.

Something that may not be of any consequence but is nagging in the back of my mind is how finicky it is to find neutral. I wonder if the valve has a blockage or is too small. Honestly I am out of ideas. Hopefully there is nothing wrong and it just needs the bigger exchanger but ask the gearbox builder if its possible to measure slippage with it installed.