Cummins 903 coolant loss

[mttopd]

Went for a short run a couple weeks ago and on the way back noticed temp on port engine rising. Throttled back and temp dropped back to normal. When I got back in I checked coolant level and found it four gallons low. Yard mechanic refilled and pressurized the system, no leaks found, no coolant in bilge, none in the oil. I had checked coolant a week prior and it was full. Next step is to use a dye and see if it comes out the exhaust. Checked database here for similar threads and found none. Am I missing something? Any experience or suggestions would be greatly appreciated.

Thanks, Brian.

 

[sgharford]

If it's the circulating pump mounted on the front side of the engine, there is a weep hole built into casting it mounts to that will allow the coolant to seep out right above the harmonic balancer. I believe the hole is slightly offset to port side, and pretty hard to find if you do not know what you are looking for. This would happen if the seal on the water pump goes bad. These weep holes were so clogged on both my engines that they were not functional. It was a slow leak, and to this point I do not know where that excess coolant went. Below is picture I just dug up from my archives. It really sucks if you have to take circulating pump off for rebuild, huge amount of labor, all front appendages have to come up. I hope for your sake it is not the pump.

 

[sgharford]

Some pictures of what it looks like to remove coolant pump. You'll need a strong back. Expect a really big labor bill from the mechanic if you don't plan on taking this ultra crappy job yourself. Further warning, if your sea water pump has/is leaking, it leaks onto the harmonic balance and will throw that sea water all over front of engine causing mucho rust. When left long enough, you will be drilling out half the bolts that hold front of engine to block due to rust.

 

[sgharford]

Just found this one, best one yet that shows you where the weep holes are. They are the 2 passages cut out for bolts as seen right above the crank shaft. By the way, this is best time to add block heater if you ever thought about it. The entire front of engine would have to come off for that too if you decided to do it down the line.

 

[mttopd]

sgharford,

Thanks for the photos, looks like a winter job. How much coolant were you losing? I'm losing at least a gallon per hour.

Thanks, Brian.

 

[sgharford]

Hi Brian, see you have a 43DC too and located in NY, mine is 1976. I was losing very little coolant, and this may not be your problem. But if it is the coolant pump (the shaft seal), it should leak out the weep holes I pointed out. Maybe throw a rubbermaid plastic dishpan under the harmonic balancer and see if any coolant collecting there after running her a bit. If not this, I'm at a loss as to where to look next or how to diagnose. There are big cooling water access plates (seperated with cork gasket) around the block, maybe one of those leaking? Also, the DCA filter would be a good place to check as easy fix (just tighten it). Hopefully not head gasket. When you figure it out, please post back what it is. I know there was at least one former 903 mechanic who use to hang out on this forum, hopefully he can chime in.

 

[rmatt]

If you're losing that much coolant and think it may be going through the eng, stand over the exhaust and you should be able to smell the coolant. It smells sweet. If you can't stand in the boat to smell it get in a dingy and get to where you can.

 

[habanero]

I had the same symptoms on my 12v71's. I would lose coolant with no visable sign anywhere including the exhaust. When i checked the oil through the dipstick the oil looked good. I finally did an oil sample which revealed coolant in the oil. Apparently the coolant was burning off in the hot engine. End of the story was a cracked head around one of the injectors. The boat ran perfect with this issue which was the part i didn't understand.

Mike
"Habanero" 1987 55'C

 

[mttopd]

Thanks everyone for your responses, I'll update when problem is found.

Brian.