5 short M925 A2 Cooling questions

[ericp351]

Hi all! I am new to these rigs, but have some experience with larger Marine Diesels and cars. Have some basic cooling sys. questions. Thanks in advance for any help/ advice.
1- My 6000 mile 1991 truck came to me with a bad temp sender. I bought one from a local International dealer, but it is for wrong voltage. I put a little 330 ohm resister in series- now reads 216 deg. after 12 miles of light driving. Not bad- would like to get it right instead of relative. Does anybody have ohms vs. temp. of sender worked out so I can "dial mine in"?
2- My fan clutch doesn't engage. May not be a problem given my light use. At what temp should it lock in?

3- What bolts should I carry (length-thread) to "emergency lock it" (fan) if ever needed off the farm?

4- Coolant flushes can get pricy for us civilians on these rigs. What is the practical way (time-hrs.-miles) to keep the cooling system up without breaking the bank> For example- do many owners use zincs or coolant additives instead of routine drain-and flushes as on little car engines?
5- Lastly- any cooling system known "trouble spots"? for example Cat 399's and 398's tended to eat up T Stats. I am sure many parts of the cooling system are proven with some weak points. A "heads up" to us new guys would really help! Thanks!

 

[74M35A2]

1. Probably easier to just get the correct sender. A lot of people part these trucks out. You could get a good working used sensor for the price of a new resistor, and not be adding additional failure points which fall out of calibration with changing temperatures.

2. Fan clutch is air actuated via the shutter-stat in the top coolant return pipe, and comes on around 200F, but, you don't know if you are there or not. They are easily cleanable/grease-able, lots of success threads here on doing so. Fix #1 first.

3. Bolts to do so are already self stored in the fan to clutch connection, just need to change their position. Check the TM.

4. Very economical big rig coolant flush is to use hot water and Cascade dishwashing detergent. A lot of places do it, and I also did it with great success. From there, the only correct way to keep track of coolant health for a wet liner engine is to check and adjust the freeze point (concentration) and SCA value of your coolant.

5. I don't believe there are any known weak spots regarding the 6CTA8.3 coolant system, but others may follow with their experience. My radiator and heater core were both plugged with minerals and I replaced them, but no engine issues. Changed T-stat just for maintenance.

 

[Jason O]

The "A2" 5tons have plenty of cooling relative to the little 6CTA motor. I very rarely have the fans engage on either of my trucks, unless I'm really working them in hot weather. I had to cover the radiator to get the coolant to 200F in order to test each system.

Enjoy the new truck!