Volvo Penta 7.4 overheats

[San Diego Ron]

My 1999 Monterey 26.2 Cruiser overheats. Pulled boat from water to replace leaking raw water pump believing that was causing overheating. Long story short with muffs on outdrive can not get water up to water pump, when I put garden hose inside boat hooked to hose that connects to inlet of pump the water flows freely out through outdrive inlet holes. Boat has closed cooling and raw water runs directly to water pump, the exit side of pump pushes water through oil cooler and power steering cooler and then to heat exchanger then out to outdrive. When I connect garden hose to exit side of pump water flows freely through everything and out outdrive. Why will it flow out but not in? Thanks for any help.

 

[Scott Danforth]

Check the water inlet casting. They get replaced ever 2-3 years

 

[bruceb58]

Check the water inlet casting. They get replaced ever 2-3 years

Which water casting? This is an SX style drive.

 

[bruceb58]

What happens if you have the muffs on and take the intake off the water pump. I know you have done it in the reverse but just curious.

Are you sure you have the inlet and outlet on the correct ports of the water pump? Not sure on that model if they can be reversed or not.

 

[San Diego Ron]

What happens if you have the muffs on and take the intake off the water pump. I know you have done it in the reverse but just curious.

Are you sure you have the inlet and outlet on the correct ports of the water pump? Not sure on that model if they can be reversed or not.

Yes I have tried having muffs on, hose disconnected at pump and not a drop with garden hose on at different pressure even at full, (even bought new muffs thinking old ones may not be holding tight enough). The water flows freely with garden hose inside boat hooked to inlet hose out through outdrive pickup holes. (The oil and steering coolers are on discharge side of pump and water flows freely through them, through heat exchanger and out the back). A mystery to me why water flows in one direction and not the other.

 

[Horigan]

That is a mystery. I would pull the drive and determine where the blockage is by repeating the water flow tests you've been doing. With the muffs on, does the water flow out the drive? If so, then try to seal the end of the hose to the transom side of the drive to see if water gets to the raw water pump.

 

[kenny nunez]

Possibility that the plastic fitting in the pivot housing that connects to the water supply hose is broken. Volvo # 3883597 Appears to be the part number.
You will have to pull the drive. Also a good time to check the alignment and grease the joints.

 

[Bt Doctur]

are the hoses routed correctly to the pump :in is in, out is out"
If yes, then check the first item past the pump for blockage

 

[bruceb58]

Yes I have tried having muffs on, hose disconnected at pump and not a drop with garden hose on at different pressure even at full, (even bought new muffs thinking old ones may not be holding tight enough). The water flows freely with garden hose inside boat hooked to inlet hose out through outdrive pickup holes. (The oil and steering coolers are on discharge side of pump and water flows freely through them, through heat exchanger and out the back). A mystery to me why water flows in one direction and not the other.

I would be pulling the drive at this point.

 

[San Diego Ron]

I would be pulling the drive at this point.

Guess I’ll have to bite the bullet and take it to a repair shop.

 

[Lou C]

Is this boat docked in salt water for the season? If so you can have marine growth inside the water intake area, and it will restrict the inward flow of cooling water to the impeller. In this case you'll have to split the upper and lowe drive housings and inspect that area and any other passageways that can be blocked and also replace the rubber grommet for the water transfer tube. Make sure that tube doen't have a hole rotted in it, I have heard of this happening on the SX drives here in salt water.
On my Cobra drive OMC had a plastic screen inside, like the Johnson & Evinrude outboard gear cases. I would get barnacles and other growth on this every couple seasons no matter how many times I painted it with anti fouling paint. What I wound up doing splitting the drive and removing that screen for good. That left the 4 large water intake holes wide open & I made up a tool out of stiff wire so I could hang over the swim platform and rod the holes out whenever I saw growth on them. That was about 10 seasons ago, no overheating ever since then. We don't have floating debris here that can clog the holes so there is no need for the screen in my boating environment.

 

[San Diego Ron]

My boat does sit in salt water at marina and when pulled outdrive was covered with tiny white worm like growth even thought painted with anti-fouling paint. Back flushed from inside out through outdrive, let water run for five minutes but saw no signs of anything being flushed out.

 

[Lou C]

My boat does sit in salt water at marina and when pulled outdrive was covered with tiny white worm like growth even thought painted with anti-fouling paint. Back flushed from inside out through outdrive, let water run for five minutes but saw no signs of anything being flushed out.

I think you might have a little colony of slimy creatures inside your water intakes! Since I pulled out that plastic screen I've been able to clean out the water intakes just using the tool I made up without having to split the drive like I did some years back. Not sure if the holes on the Volvo are big enough to do that, the Cobra has 4 large holes for the water intakes, you can easily clean it out. Some outboards have a removable screen on the water intakes you can take off and clean it out without removing the lower unit. The other thing is that the rubber grommets for the water transfer tube might be rotted out, this might allow water to pass one way, but may let air in when you try to run it on land with the muffs, or if running up on plane where the bottom of the upper gear housing may be out of the water. This would make sense if it doesn't overheat in the water at low speeds but it overheats on plane. While water will run through it going backwards, the impeller has to pull it forward and any air entering the raw water flow will interrupt the flow.

 

[San Diego Ron]

Went and spoke to marine mechanic today, told me a plastic water tube near top inside of outdrive breaks on Volvo Penta often allowing air inside keeping water from flowing. He also said to test it by putting duck tape over pickup holes on sides of outdrive and run water through the inlet hose at pump, if plastic piece is broken water will come out near top inside of outdrive. Outdrive has to be pulled to replace the 3” plastic fitting…..about $700. If nothing else wrong.
I’ll be 82 years old Wednesday and don’t think I’m up for this job even though I just recently changed bellows, shifter and shift and throttle cables.

 

[Lou C]

Wow I'm impressed that you could do that, at 82! The plastic piece is in the pivot housing, if you can pull the drive, you can replace it. They can crack although my old Cobra uses the same design (same exact plastic piece) and as long as I drained the raw water out for winterizing here in the North east, it never cracked.

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you can see the water tube grommets I referred to in this pic
I don't know which lower unit you have but if it's like the one in this diagram (SX-M) you might be able to clean out the water intakes easily....

the plastic piece the mechanic is referring to is part # 24 in the diagram, I don't think you need to remove the pivot housing to change this, easier than doing the bellows etc.

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[mwbrown25]

This plastic water pickup tube in the pivot housing was cracked causing the same issue in my 7.4gl vp.

 

[don2400]

Our past experience may help someone with a VP inboard pertaining to raw water cooling issues.
We purchased a low cost (so we thought) raw water pump online but little did we realise the pump housing had been incorrectly manufactured. The housing was 1.5mm too wide and this allowed the raw water to bypass the impeller which obviously could not create a vacuum.

Hope this helps someone!

 

[San Diego Ron]

I’m back again and still have same problem, thought it was fixed Sunday when dunked boat on trailer at launch ramp and everything was working, pulled off hose to heat exchanger then hose from exchanger and was getting good raw water flow. Launched boat and headed to my slip at marina when temperature rose to 200* and alarm sounded, turned around and brought boat home on trailer. Monday visited repair shop and owner told me that $6 plastic nipple is more than likely cracked and letting air in when boat is under way. (On waiting list to bring boat in) but today going to make a cradle to slide outdrive off and tackle it myself….pictures to follow.

 

[Scott Danforth]

pull the drive, when you remove the hose from the drive, check the fitting.

 

[Lou C]

tape over drive water intakes with duct tape
tilt drive up
disconnect raw water intake hose at impeller housing
have a helper watch under left side of pivot housing
pour water in hose and see if it leaks out the left bottom part of the pivot housing, if so then it's probably cracked. The pic of the transom mount is actually my 1988 Cobra but the Volvo is nearly the same thing, the plastic part is the same part. See part #18 the diagram, if water leaks from near there it could be that.