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High temp power train alarm

  • Thread starter Thread starter svaron
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svaron

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May 5, 2005
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105
Hatteras Model
54' EXTENDED DECKHOUSE (1989 - 1992)
Took the boat out and was cruising at 1850 and the starboard power train high temp alarm went off. We have 8v92's. What are the possible causes? I used a heat temp gun pointed at the trans housing and got a 195 degree reading versus the port of around 175 degree. After 5 mins I restarted the engine and the alarm was off. This enabled me to get back to our dock safely at idle.

I did add an extra quart of oil in that tranny last week and ran the boat for 5 hours with no issues. Is it still possible that I have too much oil? Please advise on what the correct way to measure the oil level is.

Thanks
 
svaron said:
Took the boat out and was cruising at 1850 and the starboard power train high temp alarm went off. We have 8v92's. What are the possible causes? I used a heat temp gun pointed at the trans housing and got a 195 degree reading versus the port of around 175 degree. After 5 mins I restarted the engine and the alarm was off. This enabled me to get back to our dock safely at idle.

I did add an extra quart of oil in that tranny last week and ran the boat for 5 hours with no issues. Is it still possible that I have too much oil? Please advise on what the correct way to measure the oil level is.

Thanks
Click to expand...

What are the transmissions?

Bobk
 
Detroit Allison transmission.
 
Re: Transmission Overheating

We had the mechanic to the boat, pulled the Tranny inter cool, had it acid washed and boiled out, reinstalled and the trans temp still triggered the alarm. The tranny is still working fine for now, but we are taking the boat to the boat yard to most likely have the bearings changed and anything else that is suspect once they pull the transmission. We drew oil samples ahead of the project to see what to expect once they look inside.

Any experience with part failure such as this that would cause the overheating??
 
I have one trans that runs hotter than the other but not too hot. One runs 165 and the other around 180. I don't know what temp the alarm sounds, so I'm not sure you are really overheating. What is the normal operational temp range per Allison? It may be in the manual or call Acadian Marine Gear and ask them where it should run.
 
FWIW: Overfilling will cause aeration which will cause higher temps.

When you first start the engines, how long does it take for the hi temp alarm to activate? Does it activate regardless of the power level - low speed/high speed or whether the tranny is in gear or neutral?

Bad bearings should be easily detected by the noise. If you are not getting any noise/vibration, the bearings are probably fine. 195F doesn't sound all that hot to me for a transmission under load but I don't know the specs and I'm not on the boat where I could check the Allison M20 manual. Obviously if the two trannys are running at considerably different temps...SOMETHING is different about them.

Is the transmission acting normally in all respects? One thing that could cause higher temps is if the clutches are not fully engaged. If they are slipping, the friction will raise temps. This could be caused by a linkage that is out of adjustment.

So, I'd suggest checking the fluid level - proper fluid, of course which is the same 40Wt oil that is (should be) in the engine - and the linkage for correct engagement.
 
Thank you
So the trigger point is 200 degrees. The Stbd engine overheats at 1850 RPM's after 10 mins. Once we power down the alarm goes off. The Port side I believe was 150 degrees. We drew oil samples which we have not received back yet. I will tell you that my mechanic sent the oil samples from 2013 and 2015. The silver content was as follows: 2013, 44 (critical) 2015, 26 which is considered abnormal. According to the comments the source is most likely from the torrington needle bearing cage.The port side has a silver content of 6. So there seems to clearly be something going on. We are bringing the boat to our mechanic tomorrow and will keep you posted. For now the transmission is functional. We will go out on one engine and leave the starboard engine running so the freewheeling does not do any more damage (rather than lash the shaft down)
 
I'm sure you have already taken into consideration the fact that oil samples can be very misleading if there is any inconsistency. For example, if one sample is pulled from near the bottom of the unit and another is pulled at mid level, the metals "level" in the oil can be dramatically different. It will also vary if taken at different temps, or, of course if the oil in one tranny has been in there much longer than the other.

It's interesting that the silver content is lower in the later sample; I would have expected higher if the bearings are going bad as additional wear occurred. But depending on the running time involved for each respective oil change, that would affect the amounts. That's another factor, of course. If you change oil and run for 100 hours and do a check, then change oil and run for 50 hours and do a check, the results may not be useful because they are not consistent.

I'm not sure how bearings that are NOT so bad that they cause noise/vibration can cause overheating but since it sounds like you are having the tranny rebuilt, the cause should be apparent at some point.

Just a reCHeck to be sure... the oil level in the tranny was correct, right? It is to be checked when the tranny is hot, idling in neutral. One thing to make future checking easier is to ensure the level is correct when hot and then, a day or two later, check the fluid when cold and make a file mark on the dipstick at that level. That way you can check it cold from then on.
 
Thanks...

All great points regarding the oil samples. The hours on the engines was consistent each year. Would feel more comfortable with at least 3 samples for a more average consensus. It will indeed be interesting to see what the sample looks like that we just pulled... all though by then it will be a moot point. It would still be a good comparison of the analysis versus what is really going on in the tranny. Now I did fill the oil in that tranny 2 weeks prior to the overheating. But after I added the oil, i did put 5 hours on the engines at 1850 RPM's with no issues. The oil level for both transmissions is the same. My mechanic, who I've known for 20 years and has been working on boats like ours for 30+ years, does not feel that the oil level would make the difference considering what the oil level is on the dip stick.
 
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