Mercruiser 470 Exhaust riser gasket/stainless plate

[Blufin 21]

Hello people bold text size?? Sorry..... I am running a mercruiser 470 and thought I would do it a favour and remove the exhaust riser to soak it in hydtochloric acid it cleaned up well. Now confusion time. The gasket set (2) has three holes to match the riser and manifold but the stainless plate blocks all 3 holes yes all 3... Is this a change/upgrade or a mistake? In short do I use the stainless plate which blocks of all 3 water journals/jackets.... My engine serial number is 5709796 for id as I am aware of different versions. Thankyou in advance for any help

 

[NHGuy]

Re: Mercruiser 470 Exhaust riser gasket/stainless plate

I tried your serial number in here, https://webapps.brunswick.com/literature/literatureUnsecureHrp.do which is the Mercruiser parts list. It didn't return an answer. But if you know your year and model you can search by that. Look at all versions of your motor til you get the exact same plumbing for your exhaust and cooling. Take note of the location and orientation of the gasket, etc. If your motor was cooling correctly before hand don't do water flow changes til you know it's right.
It wouldn't hurt to send pictures. A lot of folks on here know that setup well.

 

[Blufin 21]

Re: Mercruiser 470 Exhaust riser gasket/stainless plate

I tried your serial number in here, https://webapps.brunswick.com/literature/literatureUnsecureHrp.do which is the Mercruiser parts list. It didn't return an answer. But if you know your year and model you can search by that. Look at all versions of your motor til you get the exact same plumbing for your exhaust and cooling. Take note of the location and orientation of the gasket, etc. If your motor was cooling correctly before hand don't do water flow changes til you know it's right.
It wouldn't hurt to send pictures. A lot of folks on here know that setup well.

Thankyou NHGUY.. Mercury Mercruiser engines and parts tells me my engine by serial number is a 1980 - 1982 which I should have mentioned. Photos I will see how I go uploading some tomorrow. My gauges are the standard style quicksilver type. The needle usually sat around the three quarter mark/high end green. My mercruiser operation and maintenance manual cooling system water flow diagram shows a separation plate between manifold and riser stating the plate is non vented. My gaskets are vented raising my original question. Cheers for your time and help

 

[stonyloam]

Re: Mercruiser 470 Exhaust riser gasket/stainless plate

That is correct. I am more farmiliar with the later engines, but the 470 exhaust manifold is cooled by antifreeze rather than raw water, so the antifreeze is recirculated and cooled by the exchanger. The raw water citculates through the exchanger then exits into the exhaust elbow to cool the exhaust gasses. Without the block off you would dump your antifreeze into the exhaust (I think), so it needs to be there. Here is the parts page for your engine: https://www.mercruiserparts.com/Sho...&bnbr=6&bdesc=Exhaust+Manifold+and+Elbow(MCM). In a raw water cooled engine the cooling water would flow through the engine and exhaust manifold and be dumped directly into the exhaust, so no block off plate. Hope that helps.

 

[Blufin 21]

Re: Mercruiser 470 Exhaust riser gasket/stainless plate

Thankyou Terry & NHGuy. My mind has been satisfied to resemble . Cheers for your time