97 VP 3.0 Blows Circulating Hose

[happycamper]

I have a '97 Four Winns with a VP 3.0L. I've had the boat for 10 years and it has blown the large diameter circulating hose between the circulating pump and t-stat housing about 5 times. The first two hoses blew while under warranty, but the dealer couldn't figure it out; he just replaced the hose. At high RPM's, the hose is rock hard, especially if the thermostat is closed. When the engine reaches 160F, the pressure is a little less, but still too high.

I've tried to debug this for years, with no success. For peace of mind, I carry 2 spare hoses and I must keep the hose clamps very tight. I've trained my wife to always watch the temp gauge, because if it suddenly drops from 160 down to 120, the hose has blown again.

So far, I've removed and inspected the manifold, riser and all hoses. I pulled the drive and the exhaust appears to be clear. The manifold and impeller were just replaced. I also ran the engine with all belts, t-stat housing and circulating pump removed to check for possible cracks in head or block; there was no air pressure coming from these open ports (ran engine about 20 seconds since there was no water for cooling). Everything flows freely. There's no water in the cylinders or oil.

At this point, I have a strong suspicion that the supply pump is forcing too much water into the t-stat housing at high rpm's. In '99, the dealer put a plastic disc in the supply pump inlet hose. He said it was an OMC/VP fix for the 3.0L since it was getting too much water. I can't find a TSB anywhere on the web about this, and the new local dealer hasn't heard of anything like this.

Any suggestions would be appreciated. It's been a great boat and it's in mint condition since it's always garaged with the cover on.

I do have the OEM manuals, and I've read them cover-to-cover many times.

 

[CharlieB]

Re: 97 VP 3.0 Blows Circulating Hose

Slight head gasket leak adds combustion gases/pressure to the cooling system.

Proving this to the dealer and getting warranty repair of such a long standing problem?

Replace the water hose at the riser/exhaust after the water leaves the block heading for overboard, use clear vynal with reinforcing cord, Home Depot, Lowe's, local hardware store.

Show the air bubbles, combustion gases, then call your dealer and ask for the manufacturers rep to contact you to get it fixed, finally.

 

[tommays]

Re: 97 VP 3.0 Blows Circulating Hose

I do not know the cause but have read of other 3.0 volvos blowing the hose


It is staange as merc uses the same engine with the alpha drive raw water pump as the main difference

It would be intresting if you could install a PSI guage in and extra water port on the stat houseing or block and see how much presssure there is


Tommays

 

[happycamper]

Re: 97 VP 3.0 Blows Circulating Hose

CharlieB,
Thanks for your suggestion. I'll try some clear vinyl tubing this weekend. The dealer in AZ went out of business years ago, and I live in CO now. I still want to find the problem.

Exhaust gasses in the cooling system was one of my earlier suspicions, which is why I removed the circulating pump, t-stat housing and belts, and ran the engine dry for 20 seconds. There was no air pressure coming out the block, but then this wasn't a perfect test.

I'll try the clear hoses.

 

[Coors]

Re: 97 VP 3.0 Blows Circulating Hose

the water pressure gauge is ten bucks.
Read other old threads, seems like just last week, a guy had the same problem, and solved it.

 

[happycamper]

Re: 97 VP 3.0 Blows Circulating Hose

Follow-up:
To check for exhaust gasses in the cooling system, I replaced the bypass hose with clear vinyl tubing and ran the engine using my test tank (2nd pic). There were no bubbles in the hose.

I still suspect that the supply pump is putting too much water in the system. So, I connected another long vinyl tube from the t-stat housing down to the test tank (to recover the water), and ran the engine breifly at idle (to avoid cooking the riser). The volume of water coming from the bypass hose at idle was high (see 4th pic), but probably nothing unusual.

When the thermostat opens, the hose from t-stat housing to manifold is fairly soft, even though the circulating hose is still hard. I'm thinking about changing the thermostat, even though it opens at the right temp. Maybe there's a blockage in it.

 

[CharlieB]

Re: 97 VP 3.0 Blows Circulating Hose

There is a great difference in cylinder pressure running on the hose and running hard in the water.

Think of the size fire/fuel required at idle versus full throttle UNDER LOAD.

It high intake vacuum at idle only a small amount of fuel and air enter the cyl. Under load at full throttle and very little or no intake vacuum, a substantial amount of fuel and air enter the cyl. Was it Boyle's Law/ pressures/temp blah, blah, blah. Point is, a small combustion leak into the cooling system MAY NOT SHOW on the hose, a may have to test this on the lake, in a test tank, somewhere that you can throttle it IN GEAR UNDER LOAD.

It ain't easy proving a problem to be sure that you've finally found the problem. But I sure feels good when you do.

 

[happycamper]

Re: 97 VP 3.0 Blows Circulating Hose

Charlie,
Your point is well taken and I agree. Boats are hard to troubleshoot in the garage with a test tank, and very inconvenient to troubleshoot on the lake with the wife and kids riding along.

May be I'll reinstall the clear vinyl tubing for a mid-week trip to the lake, and look at it while going at WOT.