Installed new thermostat - engine temp Question

[Jack]

I had a temp issue with my starbord engine (4BTA cummins). The temp went up over 200deg, then would drop. stayed down for a while, then repeated. I wasn't losing fluids, seeing smoke etc. Port engine stayed constant at 180. I replaced the thermostat, and just to rule out the temp gauge as the problem, switched the gauges. I took the boat out, and the port is still steady at 180. The starboard is now reading 190 when under load, but drops to about 150 at idle. I'm suspecting that the new thermostat is defective, but wonder whether there are other likely causes, and whether or not it is something I can just live with

[AndreF]

Check for pieces of impellor in front of tranny cooler. When was last time you changed impellors?

[IRGuy]

I had both 6Bs running at 200-205F when I bought "Phoenix". Had both engines Rydlime flushed, but no change. Rather than chase my tail I bought a $65 infrared thermometer and scanned the coolant systems, both read 185F +/- a degree or so. I changed both gauges and sending units and both readings dropped to exactly what the IR thermometer showed. Check your sensor as well as your gauge. According to Tony Athens of the Boatdiesel forum thermostat failure is not all that common, the problem is usually elsewhere.

I found a few small pieces of old impeller vanes in the bottom of one aftercooler, and a few smaller pieces in the trans oil cooler. The aftercooler can be checked by removing the zinc plug in the bottom, and sticking your finger in there.

Good luck!

[In Memory of Vicroy]

Jack - Andre's suggestion is a good first place to start. If you have ever blown up a Sherwood pump impeller the little pieces will lodge downstream in the coolers. As I remember, the 4BTA (you have the 250 hp?) uses a raw water cooled aftercooler that is the first thing downstream from the raw water pump, and the rubber busted impeller pieces will lodge in the tubes.

Pull the raw water hoses off the intake side of both the aftercooler and the gear cooler and check for impeller debris. If all that is fine, and you have looked at your raw water impeller and its ok, go to the heat exchanger and clean it...best bet is to take it off the engine, remove the end caps and put acid in the raw water side for about 30 minutes - muriatic cut 50/50 will do fine. Also check the heat exchanger zinc(s) as they will break off when almost eaten up and clog the raw water circuit.

Probably the first thing you need to do though, if you are not getting any steam out of the exhaust at cruise, is to buy or borrow an infrared temp gun to check what your actual cooling temps are.....shoot the steel expansion tank and the area on the forward end of the head where the temp sender for the dash gague is located and compare that to your electric dash gague reading.

The Cummins Bs are way overbuilt on the cooling side and any increase in coolant temps is usually a sign something in the raw water side is screwed up....seldom a problem in the closed side where the thermostat is.

UV

[AndreF]

Don't know how many hours you have on them, but I'd check/change the impellors. Remove the water pump to do it-2 bolts. You can now buy very good ones (impellors).

[Jack]

Thanks for the advice. I do have the Tony Athens impellers already but I'll check them again and bring down the temp gun.