Volvo 225 overheat. Suspect riser gasket?

My 225 e 275 overhears after catastrophic failure last year. I have replaced all parts in cooling system. Water is getting to the engine without issue. The boat runs at normal operating temp at idle. Under higher rpm the water pressurisess the the raw water outlet hose, effectively shutting down water flow. New head gaskets. New everything. When I remoe the riser supply hose engine runs cool. Remaing hot water in riser flows out under pressure from the inlet fittings. Gaskets are cooked between manifold and riser also
Any ideas please
Thanks

Re: Volvo 225 overheat. Suspect riser gasket?

When I remoe the riser supply hose engine runs cool. Remaing hot water in riser flows out under pressure from the inlet fittings.

Click to expand...

Ayuh,... Sounds like the risers are Plugged, Solid...

Re: Volvo 225 overheat. Suspect riser gasket?

You don't say the year or anyother info.But a 225 I'm guessing around the mid 80'S.Time to replace the risers and manifolds.J

Re: Volvo 225 overheat. Suspect riser gasket?

I was tinking the same thing.(86 bayliner) I took risers off today, inspected, very little rust or scale. Made new gaskets also. So I ran engine without risers. 10 foot solid water stream from each side. Pulled rubber hose leading to y-pipe. New gaskets, tight risers, major water flow from each. Equall flow. Would easily fill bilge in few minutes. I'm certainly not sayin you guys are wrong but with this new information do y'all still think it's a manifold and or riser problem. Water is comming from both rubber nipples when on plane. As long as I stay below 2800 rpm it cools and circulates fine. I'm really stumped. I've seen rusted out risers and mine are in excellent shape compared to those. My outlet from raw water will pump while on plane or not. I may not be understanding th riser manifold situation could you help me givin the info I've provided? I've read for hours on here and can't figure it out. Also if I bypass thermostat housing boat cools fine but you guys know what will happen to my rubber exhuast hose! thanks guys

Re: Volvo 225 overheat. Suspect riser gasket?

I was tinking the same thing.(86 bayliner) I took risers off today, inspected, very little rust or scale. Made new gaskets also. So I ran engine without risers. 10 foot solid water stream from each side. Pulled rubber hose leading to y-pipe. New gaskets, tight risers, major water flow from each. Equall flow. Would easily fill bilge in few minutes. I'm certainly not sayin you guys are wrong but with this new information do y'all still think it's a manifold and or riser problem. Water is comming from both rubber nipples when on plane. As long as I stay below 2800 rpm it cools and circulates fine. I'm really stumped. I've seen rusted out risers and mine are in excellent shape compared to those. My outlet from raw water will pump while on plane or not. I may not be understanding th riser manifold situation could you help me givin the info I've provided? I've read for hours on here and can't figure it out. Also if I bypass thermostat housing boat cools fine but you guys know what will happen to my rubber exhuast hose! thanks guys

Re: Volvo 225 overheat. Suspect riser gasket?

New information, how many holes should be restricted on riser gaskets? I made new ones to match my old ones, the front and rear holes, looking down on manifold are not cut out on these old gaskets. Why? Shouldn't all 8 passages from manifold to risers be open?

Re: Volvo 225 overheat. Suspect riser gasket?

I'd replace one of the two hoses from the thermo housing to the manifolds with clear hose and watch for bubbles. You must be in the water to test, but it will show you if you air getting into the system.

I had a similar problem. It was sucking air when the boat got on plane but no bubbles off plane. You could watch the amount of bubbles increase with RPM. I could cruise all day at 3000 RPM, but over that it would start to heat up.

Re: Volvo 225 overheat. Suspect riser gasket?

Ok I will try that, I can tell you also when it does run hot, the outlet hose from the raw water pump to the t-stat housing inlet is hot and under pressure. Not supposed to be. Water should only be traveling one way to that point. Cool water in..

Re: Volvo 225 overheat. Suspect riser gasket?

Are you sure the thermostat is installed correctly and working? It doesn't sit in the intake manifold. There is a lock ring that holds it up in the thermostat housing.

Re: Volvo 225 overheat. Suspect riser gasket?

Yes don, it will only fit one way and I have it locked in with the retaining ring and the rubber gasket is in place. I checked t-stat in boiler with thermometer. It's good. Why do y'all think some of the wholes would be restricted in the riser,manifold gasket?

Re: Volvo 225 overheat. Suspect riser gasket?

It's normal for the gasket restriction.

Re: Volvo 225 overheat. Suspect riser gasket?

Ok on the gasket. I will check with clear hose tomorrow. I ran my motor hot last year. Basically changed block. Heads could be warped causing cylinder pressure leakage. I don't think so though as engine runs too good and water is not in oil or cylinders

Re: Volvo 225 overheat. Suspect riser gasket?

You should do a leakdown test on each cylinder and see if you have a leak into the cooling system.
There is a section in the link below on how to set up some clear hoses on the thermostat housing to see bubbles during the leakdown test.

http://www.4shared.com/file/50572185/e88f1d89/Volvo_Penta_Overheat_Diagnosis.html

Re: Volvo 225 overheat. Suspect riser gasket?

Agreed don, it's on my list. Just because no water in cylinder does not mean it's not pressurizing a water jacket adjacent to a cylinder. I was thinking that too. if I see air bubbles I know it sounds crazy but I'm going to isolate my cooling system by temporarily bypassing the whole outdrive plumbing.I'm going to get a 30 gal drum filled with water and a length of hose to attach straight to raw water pump inlet. After I run it and temp climbs out to 200 I'm going to quickly shut down and unhook inlet hose and connect fresh supply from drum of water. Recrank and if temp falls as I plane out at 4500 I will know I don't have any engine related issues. It's the only way I see to rule out mechanical problems with the engine. It's a simple test I should do before I dig into the drive again. I should be able to get 1 min from my supply bucket. I feel like I must do this as this engine is rebuilt and I have to know it's not engine related. What do you guys think of my test? Does it sound solid?