4.3L / V6 Volvo Penta Circulation Hose Bursting (((Issue Solved)))

[Tretatt]

Can anybody give me some information on a 4.3GL-J Volvo Penta engine keeps building up pressure and bursting my circulation hose that goes from the circulation pump to the thermostat housing. It even builds up enough pressure when I put the ear muffs on it in my shop. I’ve replaced my bellows because I was told that gases were probably escaping and causing it. That didn’t work. I’ve checked the thermostat and tested it and it’s fine. I’ve replaced the gaskets between the risers and the manifold. Still nothin I’ve been reading a few things in this forum and some are saying maybe it’s my riser manifold coming off my exhaust manifolds. Any ideas in what could be wrong before I go out and spend $750 on two new riser manifolds.

 

[harringtondav]

On muffs are you seeing exhaust water through the prop?
Is your engine running hot?
A circulating pump won't build enough pressure to burst a hose. It holds it's pressure against a closed thermostat until the tstat opens to let in cool sea/raw water.
The only thing I can think of is your engine is getting so hot the pressure is building.

Try again without the thermostat and see what happens.

 

[Scott Danforth]

The most pressure a circulating pump can build is about 20 psi

Hoses take more than 60 psi to burst unless your temps are really high

You have another issue

 

[Tretatt]

Thanks for the replies Harringtondav and Scott Danforth. I will have to look and see if there is water coming thru the prop....I’m guessing there is. This circulation hose has burst many times on me. Last season I tightened the hose clamps so tight that the hose blew in half in the middle. That cost me $75 for a new hose. So I’m trying it this season and I just put muffs on it and the hose was getting rock hard so I shut the engine off. (The engine was only running for, maybe 3 min before I felt the hose and it was getting really hard). The temperature did not get high on my end. Just normal starting temps. Like I said, I shut the boat off when the hoses stared expanding and building up pressure. I did a thermostat check and also bought a new thermostat and put it in. Both were good and opened up at 150 degrees.( I tested these with a thermometer and boiling water) I will try taking the thermostat out and see if this does anything. I am stumped. I will provide any other info if needed to help me fix this problem.

 

[Fun Times]

Volvo's have a sometimes hard to find small bypass hole inside the thermostat housing that I believe may be under & just offset to the side of the plug that appears to be seen in your photo above...And if that bypass hole gets clogged up it's been known to harden, burst or blow the U shaped hose but generally this issue shows up more with the 3.0L's vs the V6/8's but it could still be the/an issue that's hard to find.

Some have been able to clear the blockage within the thermostat housing by using drill bits but most have still had to buy a new thermostat housing to solve the problem even after trying to clear the bypass hole.

If the bypass hole or new housing doesn't solve the issue then of a few possibilities still left, the bigger one could be a head gasket issue..

Though you still need to try as a free test as odd things do happen in the marine engine world, 'Unfortunately removing the thermostat typically doesn't help tell the full story should the problem truly be the bypass hole to where again if unclogging the hole doesn't work then usually only a new housing seems to work over I'd say probably 60% of the time...It's one of those you don't know until it's tried type deals.

I know the following types of info will be of the 3.0's but the listed possibilities are still possible to help give you some sort of directions to check as well.
https://www.justanswer.com/boat/azz3...splitting.html
https://forums.iboats.com/forum/engi...pump-at-45-psi

I see you've been on this issue for about a year now, https://forums.iboats.com/forum/engi...-j-volvo-penta

Please be sure to come back sometime to post whatever you've tried and what seemed to have resolved your issue as this problem is often asked but hardly finalized online.

Thanks and good luck.

 

[Tretatt]

I want to really thank everybody in this forum. Sorry for the late reply as I work out of country one month on and one off. I was able to get my boat running on Sunday. Come to find out the thermostat housing had impeller pieces from an impeller I blew 3 years ago. Not sure why it took so long to get into the thermostat housing but I took the thermostat housing off and used a flashlight to see if I could see anything blocking any of the passages, and of course the smallest hole on the housing had an impeller pieces clogging it. I tried to access the the impeller pieces thru a hole that has an Allen wrench screw, but I could not get it out. I used extra long needle nose pliers and an O Ring puller. There was still enough room for me to poke a wire thru so I’m guessing I must have missed it at a previous time.... Not sure!! Anyway I put a new gasket on the housing and it ran just fine on the water. This was a great relief.....but, I took it out yesterday and I have another ignition problem, uggh I’ll post on the forum. Again, without this forum I would have not fixed this. Awesome way to communicate.

 

[Fun Times]

Thanks for the update and glad you were able to solve this one.

Just letting you know I changed the title name around a little bit with the hopes of other boaters still to come with this same type of issue are able to find your thread a bit easier while they're preforming an online google search.

Good luck with the new issue too.

 

[Lou C]

OK here is a schematic of the OMC/Volvo thermostat housing for the V6/V8 engines you can see the small bypass housing, that allows water to pass to the exhaust system from the impeller, this functions as kind of a pressure relief when the stat is not open (cold engine) and if it clogs you can imagine it will build pressure in the hose from the stat hosing to the circ pump. So, when inspecting run a coat hanger wire through that passage and the ones for the feed hoses to the manifolds. I actually found a piece of casting flash partially blocking this passage on one of the stat housings I've had (and this was an OE one not aftermarket).

 

[Tretatt]

Thanks Lou C!! Great schematic and explanation of the bypass hole you posted of the thermostat housing. That bypass hole is hard to see. I can see why things get caught in there

 

[Lou C]

glad you got it sorted, yes imagine how much volume of water the impeller can pump, if that is not relieved by flowing out the exhaust system the pressure all builds up in the hose for the circulating pump and the engine is not taking in any water because the stat is still closed. When the stat opens, that would relieve some of the pressure.

 

[Tretatt]

Makes sense. Thanks Lou C