290dp-e outdrive overheating problem

Hey all new here but need some help with my ad31 with 290dp-e. My engine overheats when I run over 3000 rpm. I swappped the outdrives and the overheating followed the leg. I have taken the outdrive apart 4 times checking different things. The exhaust is clear all the way through, I bypassed the leg and put in a thru hull water pickup. Like I said the problem follows the outdrive. I recently had one mechanic tell me to check the drive ratios because that is all they can think of next to check. Motor and drives were bought second hand so I'm working on that today. He also said to check if there is a stamp on the bearing housing under the zinc so I pulled both zincs and found the bad leg had been stamped M7-C not sure what this means. Any ideas would be greatly appreciated. thanks

the drive is your water pickup, so on the front of lower unit there are slits in the casting, this is where water gets in. Then water travels up the intermediate housing, and to the top of it entering 1.5" plastic (or on some older models 1.5" aluminum) hose fitting. The transom assembly S shaped hose connects there. Since problem follows the drive, you have an issue between the pickup (front lower unit) and hose fitting. Its maybe clogged with marine growth, barnacles and such? Disconnect the S hose, connect "muffs" as if running motor out of the water, open water hose and see if anything comes out thru the hose fitting on top of the intermediate unit.

I went with thru hull water pick ups because I thought that they might be plugged. there is about 12-18 inches between the pick up and the raw water pump. the pickups are oversized to make sure adequate water flow. I'm completly lost and have the local Volvo dealer confused.

Take off the drive and rotate the input shaft 1 revolution and see how much the prop turns to check the ratios. If you are still working on the thru-hull pickup the ratios are the most likely issue. Have you tried swapping the props between drives?

The thru hulls have been in place for a couple of test runs. I took off the drive today and tried turning the shaft it made almost two and a half rotations no matter which direction I went. Also there is no part number on the prop shaft. I took off the props from the other drive and they have part number (3861456) that corresponds with the 2.30:1 drive ratio.I even removed the zinc and checked for stamping on the bearing housing, good motor is unstamped, bad drive is stamped either M7-C or MZ-C. I looked it up and there are three drive for the AD31 1.78:1, 1.95:1, and 2.30:1. so I just need to figure this last piece out. I did swap props and tried to run the boat tied to the pier for a short time under load but nothing happened for the short time it ran. Open ocean I make it about a mile to mile and a half before the temp hits 200 and shortly after the alarm sounds. The strange thing is that on the outdrives there are riveted plates that say 2.32:1 gear ratio. Thanks for your time.

Hi
regarding your over heat, think you will find the fault is the steering yoke bushes and water tube, there are plastic shims to take out the slack in the yoke, over the years these shims wear away, volvo have updated these with stainless shims, we have changed many now as we had a real head ache with the first, had exactly the same symptons as yours, what happens is when on the plane this part of the drive is out of the water and the suction on the impeller begins to draw in air as the drive has dropped where the shims sit and the rubber seal is not sealing aswell, id advise splitting the leg in half and stripping the water tube out of the steering yoke, replace the o-rings and seals, replace the shims to the new stainless type.
Hope this helps, as said above we have now done a few of these because of this

Let us know how you get on

I eliminated the possibilty of the yoke leaking by going with thru hull water intakes.

so even with the through hull pick ups it still over heats???? is the correct

@volvopentatech yes even with the thru hulls it overheats. we narrowed it down to the drive by swapping side twice. we swapped props three times. we split the leg twice checking the exhaust and the bearings, the oil filter and changed oil twice.
@kimcrwbr1 we did a cleaning of the heat exchanger and complete back flush of the entire cooling system. we are pretty much convinced that some where along the way someone rebuilt this leg with a different gear ratio and didnt change the plate. the only difference on the legs is the good side has no stamp and the bad one is stamped with either MZ-C or M7-C on the bearing housing underneath the zinc.

I would consider changing props but only one drive is giving me problems the other runs fine. The legs came with stainless steel C6 props and I swapped the props back and forth on the drives and only one drive continues to give trouble. we are looking at the possibility that the two legs are geared different and that is why I'm having this problem.Even though they say that they are 2.32 it seems like someone did some work on that leg. I can get to 4000 but anything over 3000 is when I start getting the heating issue, with the thru hulls I can stop rev the motor in neutral and the temperature will drop immediatly but once I get under way again then it heats up again.

Sorry so long to respond but yes will try that later this week. Thank you and I will definatly post what ever I find the problem is so any body needing help can fix it fast. I have been out of the water for over 9 monthes I am going crazy not being able to fish.

Just out of curiosity when at full throttle underload is the boat preforming as it should ie getting full speed ? or cant you run it long enough to see ?

hey all finally figured out the problem. it turned out to be a mislabeled outdrive. took off the intermediate housing and did a manual visual check, [turned output shaft by hand and watched prop shaft turn.] and found that someone before had switched the lower units. so for now she seems to be running to specs. thanks everyone for your input and advice.