Hurth tranmission: How hot is too hot?

[Breakin Away]

Hi all, I just got back from a daysail in the hot sticky dead air of the Chesapeke. I ran the motor at 2400 RPM for awhile, which is a little faster than normal, to check for air leaks in the fuel system, since I just replaced the filters and had a little difficulty with air (fixed).

After I got back to the dock, I put the IR gun on a few things to verify temperature. I noticed that the case of the transmission (HBW-100 without any apparent cooling loop) was 145F. This was the first time I've checked the tranny temp, so I have no basis for comparison. But it did seem a little hot to me, so I was surprised.

I've searched for "Hurth temperature" on forums, TechWiki, TechNotes, and engine manual, and none of the hits referenced any recommended temparature range. I do recall awhile back seeing some generic (non-Universal) install info for Hurth transmissions where cooling loops were shown, but those apparently aren't standard issue on Catalina installs.

Maybe I'm too worried. Obviously the engine cooling loop is maintained at about 165F, so it's still cooler than that. It just surprised me because I'm not used to seeing something at 145F that can be so easily touched without some sort of guard on it. Insulation would prevent a burn to your hand, but would obviously make the temperature of the transmission even hotter.

What have you guys seen for the transmission temperature after sustained running?

[Noah]

Easily touched??...anymore so than your hot engine, or stove top? I know I'm not being vary helpful with not knowing spec tranny temp, but my gut says yes, you are too worried.

[Breakin Away]

Well, I was reaching across to shoot a temperature on my exhaust elbow when my arm came in contact with the transmission. So yeah it is easily touched by mistake when you are working back there. Now that I know, I will be more careful. But that's why I was caught by surprise.

There should be a temperature spec range, I'm just hoping to find out what it is.

[Mick Laver]

FWIW the Hurth HBW 100 (which I think you have) manual says the maximum allowable temperature for the transmission oil is 130 deg C (266 deg F). Toasty. Interestingly enough, it also says the maximum allowable engine power in continuous operation is 25kw (33.5 hp) without an external cooling unit.  Sounds like the M35BC is on the edge at max output over long periods. An oil change yearly - or more - certainty seems prudent for our engines.

[Breakin Away]

Thanks for the info. Now that I'm home, I see the temperature specs in my pdf copy of the manual. Funny, I couldn't find that section in my hard copy on the boat. I'll have to look again and see whether I'm missing pages.

Sounds like I was well within the operating temperature range.

Interesting that the M35B could theoretically exceed the limit of safe extended operation (without cooler). I can't imagine ever running near full throttle unless I was in an emergency situation.

[Stu Jackson]

Well, I was reaching across to shoot a temperature on my exhaust elbow when my arm came in contact with the transmission. So yeah it is easily touched by mistake when you are working back there. >>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>

That's the beauty of this forum:  somethin' new all the time.

I have NEVER worked back there reaching across anything when the engine was running, everk in 19 years!  Only thing close was adjusting the stuffing box with the shaft turning.

Good luck.  Glad you're OK.  Good idea to get baseline temps.

[Breakin Away]

After I got back to the dock, I put the IR gun on a few things to verify temperature......

Engine had just been turned off. Unsafe to reach while running in gear.

No burn at all, just warm enough to get my attention and shoot its temperature.

[Mick Laver]

I did a test of temperature of the HBW100 at my normal cruising RPM because I had some concerns. A friend had run into a large kelp patty in SD Bay and the boat didn't seem as responsive afterwards. I was wondering if there had been some damage to the transmission or the prop wasn't opening up all the way.

My diver said the prop was operating fine but there had been a lot of tube worm growth on it since the last cleaning. After he cleaned it things seemed to be much better, but I still wanted to check out the xmission. We ran the boat at 2500 rpm (after we got out of the 5Kt area of Shelter Island) and shot the transmission with a heat gun every five minutes. Results are below. At that speed it seems to gain about a degree a minute until leveling off at 145 degrees. We have a M35BC and a 15x9 Flex-o-fold.


Time               SOG                         Temp
1300               0 (cold)                       76
1310               5.0 (heading out)        87
1320               5.0 (heading out)        97
1325               6.8                             110
1330               6.9                             116
1335               6.9                             122
1340               7.0                             127
1345               6.9                             132
1350               6.6 (past PL)             133
1355               7.1                             138
1400               6.8                             141
1405               6.4                             144
1410               6.8                             145
1435               (engine off-sail)         125
1545               (engine off-docked)   125