671 Engine Temps

[newinlet]

My 1978 J&T 671-N 310 H/P engine seems to run warm at higher RPM.
Both engines runs 180+ at 2100 & up. The higher the RPM the more the engine Temp. creeps up. I have orig.. A/C gauges and the needle goes almost to the line after 180. (I think that is 200). I have acid cleaned both exchangers (they seemed clean) Raw water pumps are fresh, The coolant I use is final charge. I add this without water. I have replaced the senders and 1 gauge.. I have not used a heat gun to check temps. but the senders & 1 gauge is new. Sea strainers are clean. Rad. caps new

The overheat alarms have never come on (they work)
Both engines run the same Temp. The water Temp I run in is 65-70 F
These engines run perfect 2650 no load , 2500 Load 2300 Max cruise . I have been told not to worry about this but I do not want to hurt the engines. Should I try a different coolant. Any suggestions

 

[Dan Mapes]

First validate the accuracy of the guages. I am not familiar with the coolant you are talking about, but if you are using 100 percent antifreeze that is not designed to be used full strength you are asking for higher temps.

 

[MikeP]

Yes - validate the temps.

Buy some thermocouple direct-reading temp gauges and install them in the engine room(s). My helm gauges all read differently from the "real" readings and different from each other. After you determine the real temps. correlate the readings on the helm gauges and put a small mark of some sort on the gauges to show normal temp range.

 

[eze2bme]

Buy yourself one of the hand held infra red temp gauges ... bought mine from an auto supply store ... then shoot the thermostats and see what readings you get. Like you, I get different readings on my lower and upper helm gauges. I also run in water temps of 70-80 degrees ... and my temps only reach near 180 degrees when I'm running at or near WOT which is 2450 RMP on my J&T 671N's ... at 2100 RMPs my temps are normally around 160 degrees.

 

[jim rosenthal]

Are you running a mix of distilled water and antifreeze, or just antifreeze? I think a mix of the two cools a lot better than straight antifreeze. Perhaps that's part of the problem.
The digital IR thermometer is so essential a part of diagnosing this sort of problem that I can't imagine trying to do it without it. They are also a lot less expensive now.
Interesting problem- I would have thought it was the thermostate but for the fact that both of them are doing it.

 

[Traveler 45C]

A 50:50 mix of distilled water and anti-freeze is required. A higher percentage of anti-freeze will inhibit the heat transfer properties of the coolant. The coolant will not be able to pull as much heat from the engine. Your engine will actually run hotter and you’ll never know it.

 

[Nick]

Verify the operating temps with the gun or mechanical guages in the ER as noted above! The antifreeze water (distilled mix ratio should be more like 30% antifreeze/70% water to obtain better heat exchange transfer and freeze prtoction in the NE. Also note that the heat exchanger cores should be pulled and cleaned by the radiator shop in a caustic bath (not acid) to remove the silicate that builds up on the fresh water side of the core. The acid bath cleans the salt water side of the core only and does not dissolve the silicates.

 

[spartonboat1]

Re: 671 Engine Temps/NALCO

In addition to the correct mix of water/coolant, around 50/50, you should be running a percentage of Nalco, now sold under another name by the Bars Leak people. DD strongly reccommends the Nalco (current name?), which prevents microscopic bubbles from forming next the the liners and causing corrosion. Any 2 cycle DD should be running Nalco.

Carquest sells Nalco or the equivalent.

 

[newinlet]

Thanks for the advice so far
I am using Global final charge 50/50 Pre-diluted , It says not to add water or SCA's. It also says it protects against cavitation. 6 gallons per engine Tonight I am going to take readings with a i/r at the thermostat housing area while underway.....
I used swimming pool acid to clean the exchangers it seemed to do a real nice job. does anybody know what temp the warning alarm should activate ?

 

[Freestyle]

The manual says the alarm goes off at 200 and automatically shuts down at 210.

Fortunately I've never seen either happen

 

[Genesis]

My "never exceed" temp for Detroits is 195. That's where my alarms are set.