Volvo Penta 7.4 overheats

[Scott Danforth]

That is the fitting that should be replaced every 2 years per post #2

 

[Lou C]

The plastic ones, don't really go bad unless someone let the water in the raw water circuit freeze and then it cracks. The Cobra I have owned 20 years I have never had to replace it, I have a few spares just in case though

 

[Donald0039]

Are these plastic fittings still being used today in VP outdrives?

I pulled both hoses off the raw water pump to drain. I used my mouth to blow out the intake hose.

 

[San Diego Ron]

Made cradle and about to pull outdrive, stuck at about 1/2” to go, so figured good time to have a beer break.

 

[Scott Danforth]

Are these plastic fittings still being used today in VP outdrives?

I pulled both hoses off the raw water pump to drain. I used my mouth to blow out the intake hose.

Yes

 

[San Diego Ron]

Made cradle and about to pull outdrive, stuck at about 1/2” to go, so figured good time to have a beer break.View attachment 375447

Now that drive is pulled loose can’t see under there to remove hose and clamp and pull out the nipple

 

[Horigan]

Pull the drive all the way off and tilt the pivot housing up and you’ll see the hose connected to the fitting. On mine, I had to use a big hammer on the fitting end in your picture to break it free of the pivot housing due to corrosion.

 

[San Diego Ron]

Well this was not easy, pulling out the plastic nipple that I was told most likely cracked, which turned out not to be broken after all…now what?

 

[bruceb58]

Well this was not easy, pulling out the plastic nipple that I was told most likely cracked, which turned out not to be broken after all…now what?

I had a Volvo and a Cobra over a period of over 30 years. That piece never cracked.

 

[Lou C]

That’s why I said to test it by taping over the water intakes and backfilling with water via the raw water intake hose. This is described in Volvos documentation on troubleshooting overheating.
Post # 20.
Like I said earlier I’d suspect Maine growth in the water intake area and possible rotted water tube gaskets or a hole rotted in the water tube. But you have to split the upper & lower drives to check & repair those.
Post # 15

 

[San Diego Ron]

looks as if the rubber seal where the two come together may not be enough or flat enough to really seal, should I clean surfaces and use something like 5200 to keep water in and air out?

 

[Lou C]

That irregular o ring should be replaced each time you pull the drive; I coat it with marine grease to hold it in place while reinstalling the drive. While you’re at it check the driveshaft bellows carefully. If you need to split the drive I have a trick for that job! I'm still thinking your problem could be marine growth inside the drive water intake area or the water tube grommets or the tube itself. There was a member on here that had the same style drive and his water tube had a hole rotted in it. Always start at the beginning of the system, that's the water intake system. And for a boat slipped or moored in salt water it WILL need to be cleaned, that's why I tossed the plastic water screen on mine.
This my old Cobra but the way to get it apart without breaking stuff, is first make sure to remove all the bolts that hold them together (2 on each side, and one or 2 where the rear of the drive). Next, put a rod through the trim ram holes, then use two 1/2" bolts (IIFC from the last time I did it) through the front mounting holes. Then you get 3 scissor jacks one on each side of the rod, and one under those 2 bolts, and slowly and carefully jack it till it pops free. They can get REALLY stuck on there due to salt water use. On the Cobra you have to remove the water passage cover to clean it out, I've never done a Volvo so I don't know if it's the same or not, if you have the removable screens on the sides of the drive, you might be in luck. Usually the water grommets don't fail unless you had a bad overheat, then they can get melted, due to the loss of cooling water through the drive.

 

[bruceb58]

looks as if the rubber seal where the two come together may not be enough or flat enough to really seal, should I clean surfaces and use something like 5200 to keep water in and air out?

Do not put any sealant around that o-ring but make sure all surfaces that it touches are perfectly clean. I put some silicone/PTFE grease on mine when I replace it to hold it in place.

 

[Lou C]

Volvo Penta 3850935 3855695 Cobra SX Lower Unit Gearcase 1.66 1.97 4.3L V6 SX-M

Part Number(s) Included Volvo Penta / OMC Joint Venture 3850935 3855695 Cobra SX Sterndrive Upper Gearcase Unit From a 4.3L GL 1994 Model 17/27 Teeth For the Lower Gears (1.66 & 1.97 Ratios) General Application / Compatibility So 1.66 was stamped on the plate from the upper unit, but basically...

www.nlamarine.com

Here's some pix, not sure if this is the same as yours, but it looks like the water passage can be accessed by removing the cover with 4 bolts. I'd be very careful with those bolts, use some penetrating oil, heat & patience. When re-assembling any salt water used drive, make sure to clean out all the threads as best you can, and use OMC gasket sealer on the threads, it helps prevent seizing up in salt water. I use it on EVERY bolt on the drive, and mine sits in the salt for 5-6 months each year.

Yes silicone grease won't degrade the rubber but I've been using OMC triple guard grease for many years on that and impeller gaskets and never had a problem.
Clean up all that white corrosion on the pivot housing and drive mating surfaces especially around the 6 studs, and coat that area with OMC triple guard, that will prevent the drive from seizing to the pivot housing, also coat the splines of the driveshaft with it. If your u joints & gimble bearing are grease-able, grease them with marine grease when you have it apart.

I see a tub with water in it there, you aren't trying to run it in that are you? No way your impeller will prime that way, you need muffs that fit tightly esp on the Volvo because the water has to travel so far, up 18" or so and forward about 4 feet to the impeller housing.

 

[San Diego Ron]

Thanks to both of you for this latest advice, I can see that the surfaces where the rubber gasket (O ring) seal is pretty rough and with the amount of marine growth on outside of outdrive and boat from being in saltwater pretty good guess there are animals living inside water pick up holes and above. Next step is to tear into separating the lower section even if is more than I wanting to tackle.

 

[San Diego Ron]

That irregular o ring should be replaced each time you pull the drive; I coat it with marine grease to hold it in place while reinstalling the drive. While you’re at it check the driveshaft bellows carefully. If you need to split the drive I have a trick for that job! I'm still thinking your problem could be marine growth inside the drive water intake area or the water tube grommets or the tube itself. There was a member on here that had the same style drive and his water tube had a hole rotted in it. Always start at the beginning of the system, that's the water intake system. And for a boat slipped or moored in salt water it WILL need to be cleaned, that's why I tossed the plastic water screen on mine.
This my old Cobra but the way to get it apart without breaking stuff, is first make sure to remove all the bolts that hold them together (2 on each side, and one or 2 where the rear of the drive). Next, put a rod through the trim ram holes, then use two 1/2" bolts (IIFC from the last time I did it) through the front mounting holes. Then you get 3 scissor jacks one on each side of the rod, and one under those 2 bolts, and slowly and carefully jack it till it pops free. They can get REALLY stuck on there due to salt water use. On the Cobra you have to remove the water passage cover to clean it out, I've never done a Volvo so I don't know if it's the same or not, if you have the removable screens on the sides of the drive, you might be in luck. Usually the water grommets don't fail unless you had a bad overheat, then they can get melted, due to the loss of cooling water through the drive.

Thanks for the pictures and information, looks like it shouldn’t be that hard to take apart, but what about putting it back together? Will I have trouble getting things lined up like the driveshaft and can I leave lower unit on cradle and lift the top part off myself?

 

[Lou C]

That’s how I did it. The tricky part is lining up the water tube. See if you can get someone else to help you; I was able to do it myself.
The mechanics I used to use recommended splitting the drive & cleaning that area out every 5 seasons in salt water. So it’s a good thing to learn how to do.

 

[dypcdiver]

As Lou C mentioned, I had an overheat problem that only occurred at idle speeds, it turned out to be the dogleg tube that is on the water intake but buried between the upper and lower drives, it gets burnt by the exhaust gases. Number 12 in the diagram. The replacement is now stainless steel, I wonder why? Hope it helps. I did it single handed but a second hand would make it easier.