4.3 GXI - 2007 blowing hoses off

[Topcat2vin]

Hi,
I am looking a bit of advise. I have a 2007 4.3 GXI with an SX-A leg. The boat was not used last season but at the start of last season had the exhaust bellows replaced and the impeller and belt replaced.

When I went to take it out this season the fist time it split the hose from the impellet to the thermostat housing. I repaired this and 2nd outing it popped of the host from the impeller to the circulating pump. (on both occasions I was only going for 5-10 min. and only at 1200 - 2000 rpm.

I figured it was due to excessive pressure, I checked the impeller - its seems fine, I replaced the thermostat and checked the housing including pipes to manifolds, I also removed and inspected the manifolds and risers, they seem reasonably good. boat is 2007 but only done about 150hrs.

After a clean up and reinstall I ran again and still blew off the hose to the circulating pump.

Any Ideas? I think I am right in saying the exhaust has no flapper, could the circulation pump going faulty cause this? Could it be something to do with the bellows being replaced? can I have a blockage on the exhaust - how would I check this?

Also oil looks good.

 

[Topcat2vin]

Hi,
I am looking a bit of advise. I have a 2007 4.3 GXI with an SX-A leg. The boat was not used last season but at the start of last season had the exhaust bellows replaced and the impeller and belt replaced.

When I went to take it out this season the fist time it split the hose from the impellet to the thermostat housing. I repaired this and 2nd outing it popped of the host from the impeller to the circulating pump. (on both occasions I was only going for 5-10 min. and only at 1200 - 2000 rpm.

I figured it was due to excessive pressure, I checked the impeller - its seems fine, I replaced the thermostat and checked the housing including pipes to manifolds, I also removed and inspected the manifolds and risers, they seem reasonably good. boat is 2007 but only done about 150hrs.

After a clean up and reinstall I ran again and still blew off the hose to the circulating pump.

Any Ideas? I think I am right in saying the exhaust has no flapper, could the circulation pump going faulty cause this? Could it be something to do with the bellows being replaced? can I have a blockage on the exhaust - how would I check this?

Also oil looks good.

At about 1200 RPM after running for a few minutes I read the temperatures:
Bottom of Thermostat Housing 150-160F
Top of Thermostat housing 95F
Manifolds Left = 107F / Right =95F - when facing the belts
The small water line from the thermostatic housing inlet through the fuel pump to the riser goes the the right one with the lower temperature.

 

[stouchton]

I did not think it should have a hose from impeller to circulating pump? I have a 2004 4.3 GXI and the impeller (what I call raw water pump) only feeds thermostat housing. Thermostat housing feeds the circulating pump (hot water comes out of thermostat housing and heads to circulating pump if thermostat closed - if thermostat open hot water heads to manifolds while raw water heads to circulating pump).

As for popping hoses off, if they are not loose than only pressure should do this unless something mechanically is worn. I am wondering if this is the case, are you pressurizing the water jacket from something like a head gasket failure (could be cracked head or block also....).

A split hose would imply it should have been replaced a long time ago, so I guess it is possible it was a simple hose failure (split?) that caused it to pop off.

 

[Topcat2vin]

You are right the raw water pump feeds the thermostatic housing and it is turn has a hose to the circulating pump.

The hoses were in good condition and I have had a split and a popping off. I also think pressure but was wondering if the circulating pump was bad would you get some steam causing the pressure?

Do you know on the thermostatic housing if the bypass is only the small pipe to the fuel cell or if there is also a bypass channel or route inside the thermostatic housing?

The Engine has not given any trouble before this for the last 3-4 years but it was not used last year.
Thoughts I had:
blockage in leg, bad circulating pipe, if the is a builtin bypass in the thermo housing is it blocked, head gasket.

My feeling is it wouldn't be head gasket as it has very low hours and in drained down and stored in garage over winter, when running is also has never overheated until not when you can see the temperature starting to climb.

 

[BRICH1260]

I think your problem is within the thermostat housing with a clogged passage or thermostat not operating properly allowing excess pressure to build up. There are hidden bypass passages deep within the casting that can get clogged. I would start the engine and pull the feed and exit hoses from the thermostat housing and check for proper water flow. do not run the engine but briefly, just long enough to check for proper flow. if not, pull the tstat housing and probe around in there with a stiff wire and check for clogs. Also make sure your thermostat itself is seated properly with the O ring.

 

[Scott Danforth]

+1^ what he said

 

[Topcat2vin]

this is what I am hoping. Will check later today. I did inspect it and replace the thermostat but the I did not see any hidden passages. I will check again.

 

[Lou C]

Here's a schematic of the OMC/Volvo thermostat housing design, if that bypass port clogs you can see how pressure delivered by the impeller can build up and put pressure on the hose from the impeller housing to the thermostat housing. Also if they have never been checked it may be time to check the water passages in the exhaust elbows and manifolds. With these systems you need a lot of water flow IN and OUT, any restrictions will increase the pressure at the point of the restriction.
I would remove the housing, and stat, clean out all the ports, test the stat in a pot of hot water with a high reading thermometer. The stat is held in by a rubber ring that you can miss if covered with rust.

 

[Topcat2vin]

Thanks for diagram. On mine I have a small hose tail off the water inlet pipe section of the housing which has a hose to the fuel pump and from there to the right side elbow. I thought this was the only bypass. I will check for an internal one.

 

[Topcat2vin]

I still have to test but it looks like it was a blocked thermostat housing bypass. It is hard to see where it is and mine was definitely blocked.

 

[Topcat2vin]

I still have to test but it looks like it was a blocked thermostat housing bypass. It is hard to see where it is and mine was definitely blocked.

Thanks for advice guys.