loss of power, increase in temp after 2 hours running

[Guest]

I just returned from a ~100 mile round trip to Mystic, Connecticut. Some sailing, mostly motoring. Had a recurrent issue with the engine. It seems when running under load for more than an hour or two, I notice temperature slowly beginning to climb and oil pressure dropping with subsequent rough running and loss of power. Stopping the engine and restarting >1 hour later makes is run fine again.

Background - This is a late model (original) engine in a 1978 Tartan 34. Usually well maintained by me. Within the last 2 years I replaced the complete exhaust system and installed a completely new fuel system from tank to engine block. Valves recently adjusted. The engine is raw water cooled with recent impeller change. I'm running 30 weight (maybe 5W30) premium oil and Indigo oil filter kit. Also Indigo electronic ignition. The engine starts easily, runs very well, and idles smoothly. Seems to have good power initially.

I don't run the engine that hard, but do try to maintain better than 5K boat speed. Tachometer has never worked well but I know that I can get to ~2200-2400 RPMs but probably don't run it harder than ~1800 RPMs. The raw water cooling is using a 140 degree thermostat and until recently the engine has always run constantly without getting warmer than 140 degrees. On my trip last week the temp slowly crept to ~160 degrees and the oil pressure fell slowly from ~40 lbs to ~20 pounds, then engine began to run rough with loss of power. I did go down to 30 weight oil this year - I ran 15W40 in the past with no trouble.

I'm not convinced that the engine trouble is related to overheating but that would seem to be the case. I did run the engine for several hours (at lower throttle I think) with engine temp staying at 140 and no rough running issues. Any insight / suggestions sincerely appreciated.

Many thanks.

Kai
Tartan 34 'Etoile Filante'

[Baltimore Sailor]

The Universal people recommended a valve on the bypass hose to allow you to manually control the amount of water going through the cooling jacket. I have one on my boat, and without it she would probably overheat as well.

You don't say what the oil pressure drops to on your engine, but if it gets below ~10lbs the oil sensor switch will cut your fuel flow, which would cause the rumbling shutdown.

A late-70s engine with a new impeller, you say? (cue Jaws theme) Never had overheating issues prior to that, you say? (louder Jaws theme)

You may have just joined the "new impeller doesn't provide enough water flow" club, of which several of us are now members. If you still have the old impeller lying about anywhere, could you take a measurement of the heights of the lobes and pass it along to us? The new impellers measure 7/8", but some of us with older impellers find that they are a bit taller (29/32" or even 15/16") than the new ones. The new impellers don't provide as much "squish" going into the chamber as the new ones (stick out of the chamber so that the back plate "squishes" them down), which we suspect causes reduced water flow.

Sadly, we have not yet resolved this issue, though some members are trying to remove some material off the back of the chamber where the plate mates to it in hope of creating more "squish" on the new impellers.

In the meantime, I'd suggest putting in the ball valve between the T fitting and the thermostat so that you can force more water into the cooling jacket.

Good luck and keep us posted!

[Kurt]

I would remain open to the possibility that you have 2 separate issues going on here. Your temp creeping up to 160 should not cause rough running or a shut down. Fresh water cooled A4s usually run at 180 (mine does). When my engine was raw water cooled, it would have the type of temp fluctuation you are describing every 6 months or so. I would do an acid or vinegar flush and have done a pressure flush a couple of times as well to clean out salt deposits and get the temp back down. I would be mostly concerned about your dropping oil pressure when under load. Once your engine is warmed up, it should remain pretty constant - I know that once my engine warms up, the oil pressure remains rock solid. I'm guessing here, but I would imagine that fluctuating and/or low oil pressure could cause a temp increase as well.........

[thatch]

Ksturmann,
Assumming that you have either a (1:1 or a 2:1 direct drive A4) I will address another "heat builder" in your engine. The part I am talking about is the thrust bearing in your transmission which has the duty of absorbing all of the push that the prop creates and turns it into movement for your 34' boat. In my opinion, it is the most abused element in the A4 package. You have indicated that you have gone from 20/50 wt. oil to 30 wt. and that the overheating issue began after that.
Before making any other changes, it would seem like a good test would be to switch back to the 20/50 and see what happens. Although the oil and water systems are seperate, they definately have the ability to help or hurt each other.
Tom

[thatch]

"oops"

Ksturmann,
In post #4 I mistakenly referred to your previous oil as 20/50 instead of 15/40. Same principal, wrong numbers, sorry.
Tom

[Trysail]

Could be that as your engine heats up, the coil is heating up as well.

My engine temp. slowly creeps up when I motor for long periods. When my coil started to give up the ghost my engine would die after an hour or more of running. Later, it would start right up.

I purchased a high end coil from Moyer (or possibly Indigo, can't remember for sure, but they are both great companies).

[rigspelt]

As Trysail suggests, this could be a symptom of the "cold connection" problem, where an electrical component in the primary ignition circuit fails when warmed up owing to temperature-related resistance and works when cooled off. The coil is a not uncommon possiblity. Mine turned out to be a failing solenoid on a different engine on a previous boat, and in another active thread here the owner found a failed ignition switch. This presumes that your temperature elevation is within normal limits and not a symptom of a different problem I guess.

[craig deem]

Somebody has me thinking now?

I just ordered and replaced my impeller and new gasket and my temperature seems to be registering higher too?

The Universal people recommended a valve on the bypass hose to allow you to manually control the amount of water going through the cooling jacket. I have one on my boat, and without it she would probably overheat as well.

You don't say what the oil pressure drops to on your engine, but if it gets below ~10lbs the oil sensor switch will cut your fuel flow, which would cause the rumbling shutdown.

A late-70s engine with a new impeller, you say? (cue Jaws theme) Never had overheating issues prior to that, you say? (louder Jaws theme)

You may have just joined the "new impeller doesn't provide enough water flow" club, of which several of us are now members. If you still have the old impeller lying about anywhere, could you take a measurement of the heights of the lobes and pass it along to us? The new impellers measure 7/8", but some of us with older impellers find that they are a bit taller (29/32" or even 15/16") than the new ones. The new impellers don't provide as much "squish" going into the chamber as the new ones (stick out of the chamber so that the back plate "squishes" them down), which we suspect causes reduced water flow.

Sadly, we have not yet resolved this issue, though some members are trying to remove some material off the back of the chamber where the plate mates to it in hope of creating more "squish" on the new impellers.

In the meantime, I'd suggest putting in the ball valve between the T fitting and the thermostat so that you can force more water into the cooling jacket.

Good luck and keep us posted!

[longhorizon]

Thank you

Thank you all for your words of wisdom. I particularly like the failing coil suggestion. In any event, I changed the oil today, back to 15W40. Will order a new coil and see what happens. If that doesn't resolve the issue I think I will check impeller (a cursory look reveals I have both the wide and narrow versions in my spare parts bin) and if necessary will take the cooling jacket plate off and clean things out. I agree that in ordinary circumstances 160 degrees should not be an issue. It may be a while but will post back when there is more info to share.

Many thanks.

Kai

[sastanley]

Kai,
If you can be methodical enough, try each of the suggested fixes independently so that you are confident of what fixed your issue(s).

"Throwing parts" at an elusive problem doesn't always reveal which part was the solution, or possibly that a combination of them were the solution.