4D61 Operating Temperature

[rnummi]

Anyone know what the "normal" cruise temperature on the Lehman 4D61 is? I was out all day yesterday. 2700 rpm at 6.5 knots and it hangs out at around 170-180. Push it any more than that she starts climbing. Throttle down and it drops back to 180. Any empirical observations appreciated.

[kerrye]

I don't know the answer to your question but a non-contact thermometer might be useful in analyzing the heat in the engine. You can check various locations to see if there is a difference between the heat of the cylinders and the inlet/outlet temperatures of the coolant.

[Vic K]

I understand that hull speed of the 27 is a bit over 6 knots. At 2250 rpms my boat is real close to 6. 2 ( no tide no wind) with the temp sticking at just under 170. My engine seems to like that number. If I start pushing the boat past hull speed for any extended period of time, the temp number will go up. Which makes sense. After all look at the extra weight your asking the engine to push. Try running at hull speed and see what happens.
Going hull speed doesn't bother me. I do like the fact that there is extra power if it's needed. Also being a tight wad I don't like increasing the burn rate for another 2/10's of a knot.
One of my neighbors has a Albin 28 with a Cummins Turbo. Goes like a bat out of hell but it will beat your brains out if there is just a bit of a chop. You can hear the extra diesel being sucked out. And talk about noisy.

Just my old guys opinion.

Vic

[rnummi]

Well, this was the first time I had taken her out since arriving at the new slip. When people said it was slow, I didn't know it was that slow.... After a bit I got used to it though. Very nice "sedate" comes to mind. I had it up around 3k rpm and it was definitely getting a little warm. Backed it down and it seemed relatively content. I'm really loving the purr. Man that noise suppression really worked. The other A27 sounds like rocks tumbling down a hill. Anyway, thanks for the comments, I just haven't had anything to compare it to. What're the symptoms of a clogged heat exchanger or a impeller going south? Does it rocket up to 240 or?

[Vic K]

Yes on the rocket upward if the water intake gets clogged or the impeller finally goes completely to pieces. A weak or partially damaged impeller could be the cause of an temperature increase above normal. A slow increase in temperature can also be sign of a leak in the head gasket are something as mundane as needing to replenish the fresh water/coolant.

Just one old codgers opinion.
Vic

[smacksman]

Free State sat at 165F day in day out at 7mph (no knots on my GPS) at 2400 rpm - a mph plus or minus depending on wind and tide. The temp went up a bit to 180F at 3000 rpm but I never stayed there that long.
Then one day off Ft. Myers Beach it started to climb to 200F so stopped engines. Eventually found the brand new, shrink wrapped impeller fitted a month previous had disintegrated. So much so that only a few big bits trapped in the oil cooler. The rest of it small enough to pass through the cooling tubes. Why?

The problem impeller was new but I have no idea how long ago it was purchased. I bought a new spare impeller in the UK and took it with me to New Orleans. I compared it with the spares I had and the rubber vanes of the old spares were much less pliable than the new Jabsco spare. My gut feeling is that the old spares had degraded and stiffened with age and just asking to disintegrate if used.
Another item to be put on the 'replace due to age even if not used' list like fire extinguishers, flares, etc.

Roger (in the UK now Free State sold and recovering his 'body clock' eight hours out of sync!)

[tego]

Rick, As an old sailor, I feel like 6.5 knots is flying low! That temp isn't bad at that speed for that engine. If you don't know when the raw water impeller was last changed, I'd change it ASAP, or at least check it out though. Glad to hear you're going out. I've been out 8 or 9 times this month so far and going out tomorrow again after I've finished installing my new fuel tank gauge sending units. I love this boat! Ben

[Beta Don]

Rick, As an old sailor, I feel like 6.5 knots is flying low! That temp isn't bad at that speed for that engine. If you don't know when the raw water impeller was last changed, I'd change it ASAP, or at least check it out though.

I agree. A true 6.5 knots is at the upper end of the most efficient speed for this hull - You can push it faster but the fuel burn will go up much faster than the speed. We did cruise at 7.5 knots a day or two when we were trying to make a 75 nm day, but that's making lots more wake and burning more fuel

I wouldn't inspect your impeller - I would change it ASAP. Should have done that before you put it in the water. Even of it was zero hours, brand new the last time the engine ran, it's still a 6 or 7 year old rubber piece and it will shortly begin shedding blades which will plug up your coolers and make things much more difficult when you do change it. I wouldn't even keep the old one as a spare. Buy two new ones, change it immediately, toss the old one and save yourself lots of grief

Don

[rnummi]

Thanks guys, doing it now. PO ran the a/c duct right in front of the engine.... Not happy. Figured might as well swap water pump while I'm in there. New water pump, new impeller, man some day I'm going to be done plugging parts in. So far so good though. I'm still wondering about the right prop though. Don mentioned I was running the original 13" when he looked at it. I may run over to DMS and swap it out. Any ideas for keeping it in spec? 14 or 15? Also think my Guages are toast. Oil pressure and temp both never register 0. Swapping out the Guage lights for LEDs this weekend.

[rnummi]

Just reviewed you lesson on props Don. Going with a 17" 11 pitch I believe. I need to pull the boat for a day or two to finish off the odd jobs that didn't get done before she was launched. Coming along nicely though.

[Beta Don]

Don mentioned I was running the original 13" when he looked at it. I may run over to DMS and swap it out. Any ideas for keeping it in spec? 14 or 15?

Stock was a 15 I think - Mine was a 15 X 11 RH

Check how what you have works before you decide to make a change - Can you run to the maximum recommended engine RPM? If you can *just* make it to max, then your diameter and pitch are correct. There won't be any major improvement to be had by changing - Not enough improvement to justify the cost anyway . . . . unless you get a $400 prop for $50 from Don's Marine Salvage that is

Don

[rnummi]

They offered to swap any prop for 50 if I give EM the old one. Heck if you recall mine looked like it blended rocks.

[Beta Don]

I have a stock 15 X 11 RH in very nice condition . . . . nearly perfect - Let me know if you want it

Don

[rnummi]

Thanks Don, that would be great. My little prop was trying its best. The Guage comment inre a a feed disruption was right on the money. Pulled the Guage panel, retightened the screws, jiggled the slide on connections, went right to zero. I'm a happy camper. Engine shows a nice steady 160 at 2300 rpm. Another win for the experts on AOG. By the by, just swapped out all my Guage lights with LEDs. Works great, looks great. For those interested in the swap they are on superbrightleds.com for around a buck each.

[2manyboats]

Rick;
glad you found the problem with the gauges. I'm hoping to launch at McDill next Sunday and spend a couple of days on the Bay. Hope to meet you and look at all the work you've done on the boat.

Wayne