Velvet Drive fluid level check 3697 Mariner

[ron54]

1985 Carver mariner 3697, with a 72 series velvet drive 1 to 1 ratio to Walter RV40 v drives. Acquired the boat three months ago and checked fluid which was full cold to the scribed mark on dipstick shown in pic. Checked it regularly and always at the mark cold. No other marks on the dipstick. Finally did the hot check within 30 seconds of shutting down the motors. Expected the level to be higher from the cold mark, but as you can see in the picture it is towards the bottom of the dipstick. After full cool down its back

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at the scribed mark. I guess I assumed that it would be higher on the dipstick when hot, but maybe the scribed mark is the full cold mark. Would seem to make sense, because the oil coolers and lines are much higher than the transmission and would drain back after shut down.

Any thoughts appreciated, kind of bothered me when I saw this but no issues after about 40 hrs.

[bud37]

You have to find out when the check is made . I had later models of the same thing and the check was made warm immediately after shutting down within a minute.....then I marked the stick after it was cold so I could check cold.
See if you can find a manual for your series and double check the procedure to be sure as to when and how to arrive at the correct fluid level.......

[ron54]

Thanks, found the manuals, but all mention levels vary depending on cooler line lengths, angle of trans, etc. No specifics as far as dipstick readings. Apparently the total fill will vary with the above mentioned variables. I would guess (and hope) the scribe mark on my dipsticks is the cold fill that was marked when new with correct fill. Maybe someone else with a 3697 of that era may know. Edited the topic with model info.

[km1125]

I'd bet that mark is the "hot" fill mark. Especially if there's only one mark on the stick. If there's a SECOND mark, then there could be a "cold" level too. They really should be stamped with an "H" and a "C" to avoid confusion though.

This is a bit long, but explains some of the "why" on fluid level.

The difference between the "hot" and "cold" is caused by two issues. One, the fluid expanding and, two, the drainback from the lines and the cooler. On a marine transmission the heating is not as much as an issue in an auto trans on a car for two reasons... one is because the transmission doesn't get that hot as a car ( maybe 140F vs 195F) and the other is the volume of fluid. Your trans (without a reduction gear) uses maybe TWO quarts (plus whatever is needed in the cooling lines and cooler) vs a auto in a car which might use FOURTEEN quarts. So heat won't cause that much of an expansion, but drainback will cause the sump level to go up considerably. If you knew exactly how much fluid it takes to fill the cooler and hoses you could figure how much the level could possibly go up when the trans is cold.

You have a few issues with the fluid level. One, you have to have enough to fill the system (cooler, hoses, etc) and the pump so you can develop sufficient pressure to engage the clutches. Since the pump draws from a fairly low level in the sump, the level can be pretty low and you'll still get pressure. The second issue is the lubrication of parts. Many of the bearings are not lubricated with the pressurized oil (as they would in an engine or an auto trans) but they depend on their being plenty of fluid for them to rotate in. So the level has to be high enough for these items to get sufficiently lubricated. Thirdly, you also use the fluid to cool all the gears and bearings, so there needs to be enough fluid around those gears and bearings to absorb the heat generated, and transport that heat to the oil cooler so it can be exhausted. If there's not sufficient fluid level, the gears and bearings will eventually overheat and shorten their life.

[bud37]

Source of the post Thanks, found the manuals, but all mention levels vary depending on cooler line length

So you have the remote v drive, have a look at this manual and see if it applies to you.....see page #5

Don't assume here, this may help.

https://www.tadiesels.com/assets/docs/t ... l_0001.pdf

[ron54]

Thanks bud37, did not find owner’s manual, just shop manual, very helpful! km1125, thanks as well, very good explanation, but I hope that is the cold mark! I’ve only had the boat for three months but guessing it has been running at this level for years. Fluid is nice and pink with no burnt smell so maybe no damage if fluid is low. It s a model 10-18 1:1 ratio feeding Walter RV40 15 degree v drives independently mounted. The cooling line loop is probably about 6 ft total plus whatever the cooler holds. Manual (thanks again bud37) states capacity is 2 quarts plus lines and cooler, exactly as you stated km1125.

I bought a gallon of Valvoline Dex Merc which specs precisely to owners manual. This is really bugging me, so I think my best course is to warm it up and change the fluid according to manual directions, was planning that at end of season anyway. Apparently no drain plug so remove lower cooler return line, drain, then use suction pump from fill opening at top. I can then measure what came out. If more than two quarts that is likely the cold fill mark, if significantly less , it’s been running low. Does this sound correct?

[bud37]

Source of the post Does this sound correct?

Ron...if this manual applies to your equipment then the bottom of page 5 and the top of 6 explain exactly what needs to be done and in the correct order to attain the proper level then you can follow up with the cold level marking as explained.
Starting with measuring what comes out is a good base point but you still need to follow the directions to get the proper level for your installation as they are all different in some way and can be altered over the years by people before....that is why assumption is a bad tactic. It seems you are trying to do this the right way from the beginning.....good for you , proper maintenance is always an admirable goal.

[km1125]

First use the suction pump to get out as much as you can from the case, THEN remove the lower cooling (return) line and drain the rest. That way you have less risk from spilling into the bilge.

When you have that lower cooling line off, check the screen for debris (there should be a screen in that return line). Don't forget to loosen a line on the cooler to make sure anything in the cooling lines (and cooler) drains back to the case. Pick the highest one possible and don't forget to re-tighten it before proceeding.

[ron54]

Thanks for the advice guys I didn’t think about loosening the cooling line at the top of the U cooler to break the vacuum. Warming her up now bringing engine up to temp. running it at idle a little bit in forward and reverse in the slip, do you think that’s enough to circulate everything?

[km1125]

Yea, just needs a quick time in both forward and rev to make sure the clutches are full. The fluid circulates through the cooler even in neutral.