mercruiser 260 - converted to center risers.. upper exhaust hot, lower cool

[CamaroMan]

Hi guys - I recently dropped a merc 260 into our fishing boat and had a few spare center style risers. I plumber the check ball hoses to the front facing and the other 2 hoses to the bottoms of the risers.

The upper half of the exhaust where it exits the riser gets super hot but the lowe rhalf is perfectly "warm" to the touch.

Do i need restrictor gaskets between the risers and manifolds?

fyi im using the original 260 t-stat housing..

Heres a pic showing the hose routing -

thanks!

To quote:

"Now... this thermostat housing is usually used with Bravo or newer Alpha Gen II drives.
Your older Alpha One has a high pressure / Low Volume water pump.
The newer Alpha Gen II's use a High Volume / Low Pressure water pump.
When Mercruiser changed the drive (and water pumps) they also changed the thermostat housings."

https://www.justanswer.com/boat/3byi6-converted-v8-mercruiser-log-stye-manifold-system.html

 

[Bt Doctur]

All depends on what T housing you have and what gasket you used on the top cap of the housing . Do you have a plastic insert for the T stat or a brass one to retain the T stat

 

[CamaroMan]

All depends on what T housing you have and what gasket you used on the top cap of the housing . Do you have a plastic insert for the T stat or a brass one to retain the T stat

plastic - i did test it but it was a little stuck in there so i just left it as is -

 

[CamaroMan]

All depends on what T housing you have and what gasket you used on the top cap of the housing . Do you have a plastic insert for the T stat or a brass one to retain the T stat

My bad - I have the brass sleeve sorry!

Sooo after doing some checking - I have all the same parts it seems as the center riser manifold kit GLM

https://www.boatpartheadquarters.com/Mercruiser-V8-Manifold-Conversion-Kit-p/glm-58990.htm



I even had the correct restrictor gaskets in, and STILL the top exhaust is scalding hot while the lower half is cool as expected to be... where it exits the riser, telling me the fwd port is not pushing eough water up over the top of the riser and out the upper top of the exhaust pipe...

Thoughts?

The installation instructions also tell to use the closed gasket when using the check balls (which I have) done

http://www.glmmarine.com/manifolds/images/V8conversion.pdf

I do notice them mentioning brass fittings instead of the drain types on the stbd sde.. im wondering if thats the catch somehow? I have the drain type valve on the stbd, didnt think it wd make such a difference..maybe ill try run that and see - also they show using the open gasket on this type however the instructions here (same kit) say different.. to use the fully blocked gasket WITH the Tee balls, and the gasket with holes if you do NOT have the T/check ball valves..



Im about to jump onto justanswer for this one!

STUMPED!! want the boat ready soon!

thanks!

 

[CamaroMan]

fyi - brand new water pump - and same symptoms on a garden hose plumbed straight into the water hose too.. so it DEF not a supply issue - im wondering if I should block off the fwd port on the riser to force the exhaust water over the top of the exhaust.. it seems the water is flowing out the bottom half of the riser too much..

 

[wellcraft-classic210]

HMMM
Wondering if their is an internal restriction or possibly a hose routing issue

- New or used parts?

- Rust cleaned out via a rod or similar and inspected ?

- Matched gasket ? ( as in aligns well and not causing a flow restriction )

- A separate supply hose to each the manifold and each riser?


-- My 1983 merc 260 has center risers and uses stainless steel metal plates to restrict most of the flow to qty 2 of the 4 passages // the other 2 have a 1/4 hole which i assume allows for drainage at winter storage I have always been able touch any spot on them without getting burned.

The experts may have added ideas

 

[CamaroMan]

HMMM
Wondering if their is an internal restriction or possibly a hose routing issue

- New or used parts?

- Rust cleaned out via a rod or similar and inspected ?

- Matched gasket ? ( as in aligns well and not causing a flow restriction )

- A separate supply hose to each the manifold and each riser?


-- My 1983 merc 260 has center risers and uses stainless steel metal plates to restrict most of the flow to qty 2 of the 4 passages // the other 2 have a 1/4 hole which i assume allows for drainage at winter storage I have always been able touch any spot on them without getting burned.

The experts may have added ideas

Yes used - but passages are very clear.. good flow of water, a hose to each part yes- like i said the lower half is fine, the upper half is scalding hot..

The small restrictor gaskets i believe are for forcing more water thru the exhaust than back down the manifolds form the t-stat bypass.. or air bubbles. The fwd port goes over the top of the riser and out the top rear, the aft port goes out the lower half of the riser - it seems mine is being cooled alot more on the aft port/lower section that the fwd/top -

No clue - seriously and want to take boat out.. think im off to justanswer

 

[Bt Doctur]

With the check balls, the flow is out the check balls to the fitting on the front of the elbow because water must always flow to cool the rubber components of the exaust no matter what the T stat is doing. The elbow to manifold gaskets should be 2 slot /2 small holes and those hoses come from the T stat housings top cover

 

[CamaroMan]

With the check balls, the flow is out the check balls to the fitting on the front of the elbow because water must always flow to cool the rubber components of the exaust no matter what the T stat is doing. The elbow to manifold gaskets should be 2 slot /2 small holes and those hoses come from the T stat housings top cover

Yes - thats exactly how I had it - I even removed one elbow to confirm. Im wondering if the spring is too weak it isnt building up enough pressure to go over the top of the elbow.. only the lower section

 

[wellcraft-classic210]

Can you pull hoses momentarily and compare ?

 

[CamaroMan]

maybe- we are busy moving our shop so really tied up this week- just stumped! I seem to have the GLM kit with the SS 90 degree bends that come with the conversion kit as well.. just doesnt add up - im sure the spring tension is too low perhaps to build up enough pressure to spray over the top half of the risers...