Cummins 4BT questions

[Shannon Ritzert]

Hi guys, I hope everyone is enjoying their Saturday.

I have been perusing ya’lls forums for about a month now, in an attempt to answer a few questions I have. I’m not sure where to begin, so my apologies if I write to much info.

My name is Shannon. I have been in the marine industry as an inboard technician since 1992. I own a small boat dealership in North East Texas. I say that because I don’t have limited knowledge on boats and inboards, but I am completely out of my realm of knowledge on diesels. I know some of my knowledge will crossover, but after reading in these forums, I see I have a lot to learn.

So, I recently purchased a 1976 Bertram 28 Flybridge Cruiser that has twin cummins 4bt’s. I intend to spend the fall and winter months getting everything dialed in on it. In transport, the propellers were damaged. I sent the props in to Baumann Propellers to have them repaired. I also had a few gauge issues that I am sorting out. I also intend to install boost/ egt gauges. In a nutshell, I am trying to learn the boat, and engines to get everything into specs per prop load, fuel efficiency, to not overload the engines, getting the right props installed etc. Being a technician makes me pretty anal when it comes to having things operating perfectly.

The first trip out on the boat after getting the reconditioned propellers installed. My port engine ran hot under load. At idle (which this engine was idling at about 650 rpm) after about 30 minutes we were operating about 160-165. From a gas inboard standpoint, that is a perfect temp. Under a load at 2100 rpm this engine was at about 210 degrees. I immediately knew there was a restriction. I idled the boat back to the dock. I removed impeller housing, trans cooler, water strainer, and heat exchanger from both engines, and flushed all the hoses. I found impeller fragments packed on the suction side of the impeller housing, and other fragments in the hose from the water strainer to the impeller. No surprise there, as I deal with this problem daily in my shop. I also found the zinc inside the port heat exchanger was broke, and restricting the bottom portion of the exchanger. I cleaned / acid dipped all my components, and reinstalled everything. I also replaced the temp and oil pressure gauges before the next trip out.

The second trip out, lead to some other concerns with the cooling system. I installed faria gauges. The port temp gauge worked, the starboard gauge did not work. I learned in diagnosing the starboard gauge, that the temp sender is installed in the water jacket on the back of the turbo. However, where I would think a temp sender be installed, there is an early warning sender for the early warning overheat system instead. I also learned that the turbo has a water jacket. The port engine now under a load at 2100 rpm holds right at about 202. In reading the cummins 4bt spec sheet provided on ya’lls web page, this is acceptable, but it to close for comfort to me. T-Stat modulating range is 181-203. I didn’t push the engines any harder, but I would be willing to bet this temperature would increase with RPM. I used my IR remote thermometer, at idle only, and the temp at the sender was 106-109, while the gauge was at 125. Before I start chasing down an inaccurate gauge issues, What are yalls thoughts on the temp sender location for the gauge, is this the right place for the sender? If its not the right place, wouldn’t the temperature be higher at the turbo?

I am also trying to understand, or figure out Max Sustained cruise RPM. I have not been able to find anything but Max RPM on the engine Data tag at 2800 if I remember right. Sorry for that, as I don’t have the tag in front on me. Maybe its different on diesels and Max RPM is acceptable?

Topic

[Shannon Ritzert]

Hey Tony I appreciate the reply, and help.

I am trying to work through #1. I dropped my strobe in the water this year, and haven’t replaced it yet. I think I have to use it about once every five years, and was waiting for a good excuse to replace it. Most things I work on now, you just plug in to the comm port, and get your readings via diagnostic software.

Regarding #2. The sender that is in that location on my engines looks identical to the picture you attached. I assumed that was for the redundant system that is on the boat already. The reason why, is when I ground that sender, I have no gauge deflection. When I ground the sender on the turbo, the gauge deflects. The sender that lets the gauge deflect is a one wire by the way. I wonder if its possible that they used the factory sender as the switch for the redundant system. Seems I have some wiring to figure out.
Regarding the redundant alarm. We used to use these back in the mid 80’s to mid 90’s as a pot type junction before the sounder in which you turned the pot to adjust the continuity that the switch fed the junction. (I don’t know if that makes sense) I assume this system is about the same, but if not, do they make a switch for the system that is set to trigger said alarm at 195?

I already remaned the raw pumps (new wear plate, and cam) they were the worst I have ever seen. There was no wobble in the shaft/bearing yet, but I do intend to just replace the pumps over the winter when I get the boat to my shop. I have rebuilt plenty of raw water pumps in my day, and do not enjoy it at all.

I actually thought that expansion tank was adequate. I don’t mean that argumentatively, it just shows my thoughts were wrong, and its the last thing I would have suspected causing a problem. I will put a larger expansion tank on. How do you feel about the heat exchanger? I was thinking it was small. When you say belt wrap, are you referring to the serpentine belt routing? Mine looks identical to the pictures I’ve found on yalls web page, unless I am missing something.

You completely got me stoked by your opening comment about 20k hours on a 4bt. You’re so right about it being unsociable until about 1k. My brother in law put one in a jeep and called it the paint shaker.

Thanks again for the guidance, I really do appreciate your time.

[Tony Athens]

Shannon, Welcome aboard–For sure you came to the right place.. Actually, the 4BT 3.9 Cummins was really the first Cummins engine I ever put my hands on and then installed —-In my Bro’s 1st boat in 1985 and it had over 20,000 hours on it before we sold the boat.. It’s a rock solid engine, but as you possibly already know, it’s a tad unsociable below 1000 RPM and in a boat like yours, you have to ask for every pony is has to get the performance you want.. No biggy, just read below..

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Let’s see if I can help you for the long term..

#1—I ‘d say #1 is to be sure your gauges are working & reasonably accurate..

#2——-Pic attached of where both Cummins and I think the sender shout go—Just before the thermostat outlet..

#3—Cooling system———–unless the seawater pumps are less than 3 years old (regardless of hours) , most likely the cam & inner wear plate are worn or corroded to where that are not working up to spec.. You need to REMOVE the pumps, remove the aft housing and impeller—Wiggle the shaft to check for bearing wear. Remove the cam and inner wear plate –Look at them carefully.. IMO, the pumps are not rebuild-able other than the wear plate, cam & impeller. The pump itself is not for the timid to take apart and then put back together should a water seal or bearings need replacement

#4———–The cooling system on this engine is marginal at best and if you want to run the boat on plane, ( meaning you be at close to asking 90% of what the engine has to offer, IMO the entire cooing system need to be upgraded—You have ZERO reserve as to cooling capacity, and I mean ZERO.. The engine does not even has a proper expansion tank that meets Cummins own specifications, yet they have used it on that engine since 1988-ish…Think of it as a BULGE in the thermostat outlet coolant hose with a fill cap. Basically you need to set the engine up cooling plumbing wise like a 6BT 210, including the belt wrap on the front.

#4——–Be sure you have a redundant 195F coolant alarm switch—Put it on the turbo where your current sender is along with a loud warning device–Test to the switch be sure it works–Close on rise to active some reliable alarm circuitry

#5———–Install a high-flow 160F stats

#6——Check your current tachs for accuracy—You engine should reach close to 3100 RPM in neutral, engine warm, no load……….Using a strobe at about 2500 in neutral at the dock is the best way to insure tach accuracy.

#7———-If want the most out of this engine, then accomplish 1-6 above and prop to reach an accurate 2900-2925 RPM with the boat loaded as you use it. Then you can safely run at 2700-2800 RPM with confidence, but only if you do all above.

Tony

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