6V92 overheat problem

[Aviator-767]

Hi Guys,

I have 2 6V92 TIB's in my 1988 sports convertable which I recently bought.

I did sea trials and the stbd engine over heated at max thrust. At max thrust only 1900 RPM was acheived. The book says 2300 is the normal. The props are 29 X 33 these are said to be the correct size for the boat? 2500 RPM is acheived with no load. If the engines are reved with no load an initial plume of black smoke is emitted then they run clear.

with load at 1500 rpm some black smoke is evident, but the temps remain normal. The previouse owner installed an engine room temp gauge on the stbd engine but not the port?

I'm wondering where to start? To cure the problem with the black smoke and the low max load RPM. Will that cure the overheat problem. The fuel filters and air filters I have renewed also the oil and filters.

Changing the props to a finer pitch would reduce the load but would that cure the overheat problem? Why is it only the stbd that overheats?

The raw water flow is good but possibly I could change the impellor and or the thermostat?

Maybe the heat exchanger is scaled?

Does anyone have any practicle ideas?

Thanks,
Aviator-767.

[Glory]

Is this a new issue, are the sea strainers clean, seacock open all the way, is the bottom clean, is the prop bent!

JM

[saltshaker]

There are a lot of possible issues. You most likely have more than one factor causing the overheating and rpm loss. How hot did the engine get? Did you have an engine survey performed? I would start with performing some maintenance and see where you end up. Unless you know the engines were serviced recently, I would clean the heat exchangers and cooler, replace the impellers, change all fluids, service the strainers etc. What condition is the bottom and running gear in? A fouled bottom will slow you down and can cause you to run hot but I would expect the port engine to loose rpms too. If you still have issues, then you need to check the running gear and engine. Hard to say what may be the issue. Could be injectors, turbo, air restriction, to name a few. How do they start when cold? Any excessive smoke or cranking?

[madhatter1]

If you just bought the boat you need to do a full PM to establish a baseline of condition to move forward. Above posts are all valid possibilities but you are chasing ghosts without a qualified mechanic eliminating the basics. Include props, bottom cleaning, intake filters, and fresh fuel filters before looking for a mechanical problem. Don't know this cause I'm smart, just made the mistakes.

[Dan Mapes]

Sounds like the prior owner was chasing it if he put a temperature gauge on the hot engine...

Ditto all of the above.

BTW a little puff of smoke at initial throttle up would not bother me. A big dark cloud would. Since you have proof (?) that the oil and filters have all been swapped, I'd start with a diver or haul out to check and clean the bottom, perhaps pull the props and have them scanned after checking out the flow and perhaps boiling out the exchangers if the boat has been kept in salt.
You might check the micron size of the filters that were installed, and if it has secondaries were they also swapped out?

[SKYCHENEY]

I agree with all of the above regarding performing all of the maintenance items so you know where you're at. Then you may be able to troubleshoot from there.

On the temp issue, don't forget to check the thermostats. I recently had one that was only opening about 2/3 of the way.

[George]

if your in the south, check for barnacles in your system as a possible cause of overheating. What do you consider overheating anyway? Most engines at WOT heat up. Tell us about the boat, size, etc. what 6V92's, 500 hp? 535, 550?

as far as the 1900 RPM is concerned, this could be from a lot of reasons
1. Pitch on the prop is out of whack. Check the stamps on the hub to make sure they are a set.
2. Fuel restriction
3. Air restriction
4. Governor adjustment on the mechanical units.
5. Turbo issue
6. Blocked exhaust riser from rust etc.

[bobk]

My port strainer at the last cleaning had a bunch of barnacles, starboard had an eel in it. Jelly fish in the gen strainer. Wish the latter were the edible variety!

Bobk

[Dan Mapes]

You could probably open a sushi shack with that kind of luck.

[MikeP]

Barnacles on the running gear can EASILY cause what you are describing and it doesn't take many. Barnacles on our 53 changes the top speed from 18K 2300 RPM to 11K at 1900 RPM. It happens in 2-3 months of sitting.

That's the first thing I'd look at. All the other stuff comes later. Your no load RPM looks fine.