cooling action on a Perk T6.354

Diesel folks,


I took the boat (1980 mainship mk1) out on a maiden voyage this past weekend on the western LI sound and had a question. I was running her from the lower station and was at 1900 rpm for a good 15 minutes and the temperature came up to 190ish and seemed to settle there. Shouldn't I see the temp drop slightly after 180 when the thermostat opens or does it do that process without a fluctuation in temperature? I wanna say the water temp was in the high 50s. I was out for a good 30 min tooling around at various speeds and noticed when I got back to the dock that the water in my, hot water heater which has coolant running through it wasn't that warm.



Thoughts,
Chris

Thermostats usually open gradually over a temperature range. As a result, the temperature doesn't drop as they open so much as the rate of gain slows down and levels off. At least that has been my observation. Others may have a more careful eye or know more.

My current perkins 6.354(M)s level off ~175 F. My prior boat with 6.354MGT engines leveled off significantly higher. I think the difference was the thermostat installed, as they come set for different temperatures, more than any difference in cooling system or cooling system maintenance.

John,
I have never owned a Perkins, except my small Volvo sailboat engine was a Perkins that was labelled and marinized by Volvo.
When you say maiden voyage, is that "first of the season" or "first since you took over ownership"? Are you sure that the cooling system is operating at peak efficiency? Maybe the raw water side could use servicing for things like calcification, impeller bits, zinc bits, etc.? Maybe the coolant side could use a cleaning with new coolant, new pressure cap, or even new thermostat? 190 seems a bit warm to me with a 180 thermostat? and after a 30 minute run with temp readings of 190 the hot water should have been hot.
Just thoughts...... you really don't want an engine overheat as damage can be done very early with higher temperatures.

Do you know that the gauge is accurate? KISS principal says check the simple stuff first. Get a non contract thermometer and see what it says the engine is actually running at. If it is 190 then it is a bit hot. Check some of the things mentioned above, but do the simple thing first before you rip into the engine.

Yeah, it could take a bit more than a half hour to heat the water in the water heater; mine did when I had one linked in to the engine coolant circuit. I would suggest finding the coolant temperature sender on the engine a shooting it with a reliable IR temp gun to get another idea of where the temperature really is. It is not impossible to find a difference, and I think I would want to see ten degrees difference or more before I began to lose confidence in the sender/gauge combination. And DO consider all the excellent thoughts sent your way about cleaning the system. I like shooting some Barnacle Buster through there every 18 months of so; it never fails to dirty up the solution pretty well, and my boat engine is freshwater rinsed every time it is run.

Guys,
Maiden voyage this year, have had the boat for 10. I rarely operate her from the lower station but I did circulate some muriatic/water through the raw water side of things at the dock for a 1/2 hour this season pre maiden voyage. I wanted to keep an eye on the engine to check for anything that might have been amiss. So I naturally thought that if the thermostat was opening I might see a dip as the temp rose. I can do the infrared temp gun on the next outing to see if my gauges are accurate. The acid mix came out pretty funky, do you suggest straining it and running it again or do I make a new batch?

The acid in the raw water side has 2 ways of doing it. Either let it get sucked in and then sit for about 5 to 7 hours and then start up the engine and expel it out the exhaust. Or unhook the water intake, remove the impeller and use a pump to circulate it through the engine for a while. I just did the sit and soak method on mine yesterday. When I did it 5 years ago one engine dropped 5 degrees and the other engine dropped 10 degrees.

John,
If you have not had the raw water components serviced off engine in the 10 years you have owned the boat, then my guess is it is time. Running acid through the components on engine, is a "stop gap" method of reducing temperatures mid season to "get through the boating season". It will not remove impeller bits, or all of the zinc pieces that can accumulate over time. O rings or seals should be replaced, and each component (such as heat exchanger, gear oil cooler, etc.) should be pressure tested and repaired or replaced as needed. We do not want salt water where it is not supposed to be.
I agree with Dave about ensure that your gauge is reading correctly as a first step. However, if real servicing has been left for 10 years, then it is time.
Many marine diesel mechanics suggest this as being essential.