View Full Version : riser issue

06-17-2013, 09:36 AM
over the weekend I had the port side exhaust hose fry. Twice

the water shut down in the exit ports around the exhaust, we tested with the hose and breaking the system at certain points and pulling the various plugs in the manifolds and the risers were clear up to the end dumps but would not dump any volume of water out the back.

We performed some angioplasty around the water channels and it seemed to flow much better then when the motor ran and warmed up it shutdown again after the long tow in it started up and pumped a ton of water out of that side??

motor never went above 170-180- degrees it just pumped more water out the other side, I caught it both times by the smell of the hose frying. If it is blocked with crap i can understand but why it shutdowns when hot and then opens when cool has me stumped a little.

the culprit osco center risers ford 302 with a holman moody crossover system

06-17-2013, 03:37 PM
Are you running a thermostat? Is the thermostat bypass port clear? I realize these are common to both sides, but something weird could be happening in there. From the housing to the exhaust, there shouldn't be much that is temperature sensitive.

06-17-2013, 04:55 PM

we broke apart the system it was putting equal amounts of water thru both sides of the crossover and plenty of water out of the top of the riser just not the back of the riser.

06-17-2013, 08:01 PM
Matty disconnect the hoses going to the risers, put them into a bucket start to see if in fact you do have equal flow. It may be an issue before the block.


06-17-2013, 08:36 PM

i had the hoses off the risers and at the cross over T fitting coming from the t-stat housing equal flow hooked up the hoses but left off the riser equal flow hooked a garden hose directly to the port riser had a trickle out of the bottom of the exits pulled the top plug on the riser had water flow. took the manifold off ran a sawzall blade around the water exit channel by hand broke a lot crap free

this was the result water flow

06-18-2013, 01:00 AM
Just because your temp sender on the water pump or intake or whatever doesnt show an over heat doesn't mean your risers are being adequately cooled.

Obviously if you are burning hoses you aren't flowing water.

Be careful about filling cylinders with water. If your manifolds are failing and the motor is dying, it might be because water is getting into one side of the motor which can cause other damage. Then one side pumps out a lot more water than the other, could be because it pooled up in the cylinders. I'd say time to pull the manifolds for inspection.

06-18-2013, 07:04 AM
Dang I can see why you are stumped!

06-18-2013, 07:40 AM
Had a somewhat similar issue with a customers boat. After running it would shut off. If it sat for a while it would restart and could be fine for along time and then it would shut off again. Ended up finding a glove in the fuel tank that would occasionally block the pick up.

Maybe you sucked up a piece of plastic that is blocking one side for flow. After sitting like you stated, it falls free and allows water to flow again.


06-18-2013, 07:59 AM

when we pulled the exhaust hose off we connected the garden hose to the flush valve and water would flow out the starbd. side and trickle out the port we pulled the top port riser plug and water flowed freely and with good volume. there was no real space between the stainless inner gas exhaust pipe and the outer cast iron water jacket. We used a hanger and a thin screwdriver to clean out the area between the two as we did it with the hose on you could see the trickle on the bottom open up and the flow started on the top.

dumped it back in and ran fine then on the run after a good run under load it happened again. After the long 10 mile tow in when being dropped off at the dock I started it to get the last 50 to the ramp and it dumped water out of both side fine??

yesterday I pulled the port side and used a saw zall blade and worked that around that channel by hand the video I posted is the result with it connected directly to the garden hose. looks like plenty of water to me.

I was thinking that there may be area that was partially blocked and when that area heated with expansion it choked off water flow?


I was concerned a little about the motor but it only has about 5 hrs on the rebuild and it runs like a scalded dog and if water is pooling in the cyls it would think hydro lock. while it is running I pulled the water intake hose to that riser and it is flowing plenty of water at decent pressure, then pulled the top plug and water flowed at first it was very hot just sitting in the riser getting heated by the exhaust runners then as the flow began it cooled down.

for grins and giggles I am pulling the t-stat just in case it is disrupting the flow the the T fitting

06-18-2013, 08:43 AM
Is it possibly a pressure thing? Maybe one of your hoses on the port side is not stiff enough and is collapsing under suction?

...just throwing something out there.

06-24-2013, 11:01 AM
found a lot of info online, looks to have been the end dumps on this type of riser are prone to crud blockage especially in a saltwater raw cooled system which it was for a few years. tried replacing the risers they are mated to the manifolds for life now . have cleaned and tested both sides will see . it looks like I might need hiteks in the off season.

Thanks for all the input guys :)