Temp gauge in 2008 R25 mercury/cummings diesel

[bryant]

During a ride on my boat it was pointed out to me that the temp gauge was reading right at 200 degrees. The temp outside was in the mid 90s so the water temp was very warm. I haven't been able to find any information on what the normal operating temperature at WOT should be. I backed off and the temp dropped back below 200. When I mentioned this to my local marina mechanic he said it was too high and that I should have the heat exchanger serviced which would entail pulling it from the boat disassembling it and cleaning which could run between 2k to 3k. So my question is what is the normal operating temp for this engine, is there an over temp alarm, when does the thermostat open up and could a faulty thermostat be my problem. Right now I am not using the boat because I am concerned that running the boat at this temp will damage the engine.
Thanks
Bryant

 

[knotflying]

Not sure if the Cummins is the same as the yanmar in your model, but they tend to run hot at high RPM. Check that your intake is clean and installed facing the correct way. Make sure you are not loosing suction via the toilet. Make sure you are not clogged with weed in your oil cooler. When you open it up (oil cooler) check out the condition, it will give you a good indication of your heate exchanger condition. I also suspect that the intake for the raw water is too small and should be larger. The heat exchanger service would be the last thing I would do.

 

[bryant]

Thanks I will check it out.
Bryabt

 

[PanaSeaAh]

Same boat, same power plant. At high RPM (80%) it warms up to 185F to 187F, regardless of load, in 70 deg. water. If water is cold it takes a long time to get there. That is with new water-pump impeller and a perfectly clean intercooler. Fresh water. Note that page A-3 of the cooling system specs states that the thermostat starts to open at 176F and is full open at 203F. It does not state a "normal" temp. Would that indicate that you would not be overheating unless you rose above 203F, which would indicate that full flow would not be keeping up? Manual also states that a stronger concentration of coolant is recommended in very warm waters, which is defined as above 90F. Not sure if this is to increase the boiling point or improve heat transfer; perhaps both.

 

[PanaSeaAh]

Suggestion: Assuming the intake, strainer and water-pump are all in good shape, take off the discharge hose from the water pump where it attaches to the intercooler. Only have to loosen one clamp at the elbow. Use an otoscope attachment on your phone (you need one of these if you own a Ranger) to "see" into the inlet end of the intercooler. If the seawater tubes are not obstructed, you are good. If there is debris in there, you have to decide whether to take off the inlet elbow, or do some extraction. I cleaned mine with a 3/8 hose with a wire in it, attached to the shop vac. The wire lets you bend the hose into shapes that it will retain while you are fishing. If there are critters in there, there are lots of other posts on how to deal with that from the salties in the group. If it is clear, you can put the hose back on and you haven't spent a dime. 😎

 

[NorthernFocus]

Per the prior post the engine literature does not indicate "normal" operating temperature. Thermostat starts to open at 176 and is full open at 203. This basically means that if the engine is operating above 203 then it is no longer in control.

During a ride on my boat it was pointed out to me that the temp gauge was reading right at 200 degrees. The temp outside was in the mid 90s so the water temp was very warm. I haven't been able to find any information on what the normal operating temperature at WOT should be. I backed off and the temp dropped back below 200...

Does this mean that when the engine was hot you were operating at WOT?

...Right now I am not using the boat because I am concerned that running the boat at this temp will damage the engine.

If your answer to above is "yes" then you are correct, operating in that regime will likely damage the engine. The engine is not designed to operate continuously at WOT. Do you have any additional data on operating temperatures at lower loads?

 

[bryant]

Thanks for all the replies
As for the intercooler. I have only had the boat for 1 1/2 years and don't know if it has ever been cleaned. The last owner was a mechanic and other than oil changes and normal maintenance did not keep any records.
I was operating at WOT. When it reached 200 degrees backed off and the temp dropped back down.
Thanks
Bryant

 

[NorthernFocus]

...I was operating at WOT. When it reached 200 degrees backed off and the temp dropped back down.

The engine has an "HO" rating which is defined by Cummins as follows:

High Output (HO)
This power rating is intended for infrequent use in variable load applications with a load factor of 10-30 percent. Full power is limited to one out of every eight hours of operation. Reduced power operation must be at or below 80 percent load.

Interpretation:
Load factor is how hard the engine is operated on average. This is best/easiest defined by average fuel consumption divided by WOT fuel consumption. At rated HP the engine burns 9 gph. So on average when operated within the design window fuel consumption should be between 90 and 270 gallons for every 100 hours of operation.

The Mercruiser control panel indicates engine load so this is very easy to manage in real time and to run the engine within the intended operating load. Before getting too carried away with cleaning heat exchangers etc. I'd see how the engine runs at 80 percent load and below.

I've not found anything in any of the engine literature for design cooling water flow/temperature. But if you are operating in 80 degree water no doubt the engine is going to run warm. Of course you want to make sure the impeller is in good shape and there are not obstructions in the sea water inlet. And it might be a good idea to be aware of sea water temperature and see how the engine runs in different seasons. If you trailer the boat and could drop it in a different, cooler body of water(like a nearby lake?) for a test that might provide useful information.

Hope you get things sorted out and can enjoy the boat.

 

[bryant]

PanaSeaAh
You mention a "Perfectly clean intercooler". The service manual states that the intercooler should be serviced every 500 hrs. I could not find anything in the manual that describes what a "service" consists of and how to perform one. Is there another manual I should be looking at? Does the intercooler have to be removed to be serviced?
Thanks Bryant

 

[PanaSeaAh]

The statement "perfectly clean intercooler" was based on the video inspection with the otoscope. It was not disassembled, and I have not reached the 500 hours yet. Even then, being a freshwater boat, I will probably just do the video inspection and not take it apart. OTOH, it one of the few parts on this boat you cannot not only see, but get access to without a great deal of contortion. 😀

 

[PanaSeaAh]

The statement "perfectly clean intercooler" was based on the video inspection with the otoscope. It was not disassembled, and I have not reached the 500 hours yet. Even then, being a freshwater boat, I will probably just do the video inspection and not take it apart. OTOH, it one of the few parts on this boat you cannot not only see, but get access to without a great deal of contortion. 😀

 

[knotflying]

The perfect service of an intercooler would be a removal, disassembly and then a bath, reassembly with replacement of any o-rings and gaskets. The other alternative would be to circulate ridlyme of barnacle buster for an hour or so through the system. This will require removing the impeller and then reinstalling cover. Then create a "loop" with a pump and an intake hose and outlet hose going into a bucket with the solution. Circulate a bit and then let it rest. Do this for at least and hour. I used my raw water washdown pump for the circulating pump. When done circulate freah water and then put in a new impeller. Hook everything back up. Run engine and check for leaks.