I am praying there is some help here; I have 2006 formula 400ss with twin 500 EFI's only 250 hours. The port will not stay running. Starts but stalls unless you manually massage the throttle.... shipyards through troubleshooting felt it was thermostat. Ordered new thermostat and then proceeded to take Aluminum Intake Manifold and Thermostat Housing to see a bad thermostat. However due to salt water damage putting them back housing back on the AIM does not seem feasible. Shipyard can not find the parts. Mercury says they stop making them 10 years ago; Does anybody have any information on this; I have checked 4 or 5 distributors and none of them have the parts;

<!--td {border: 1px solid #cccccc;}br {mso-data-placement:same-cell;}--> Mercury part number 849900t3 Aluminum intake Manifold
<!--td {border: 1px solid #cccccc;}br {mso-data-placement:same-cell;}-->
Mercury part number 849927t1 Thermostat housing.

Both engines run so well but now I can not keep the port running it just stalls, sometimes hard to start.

Thank you for any advice....

There is an upper and lower on eBay

https://www.ebay.com/itm/31473992000...mis&media=COPY


There are threads on here to modify a T-stat housing or just pay Mercury ransom if nearly $1k. Mercury has become ridiculous on pricing for parts.

Unfortunately Mercury discontinued this part 10 years ago...
Thank you for your help!

Not that its gonna help you with the parts, put the odds that your thermostat has anything to do with your engine staying running is about zero. I'm not going to guess sensors but one of them has a problem most likely

As far as the problem with corrosion, without seeing a picture, its hard to give you a fix easier/cheaper than a new part. The thermostat housing is available all over the place, just at a stupid $1000 and going up from there.

This one ?

Best price i found doing 30 second search for OE part is $733 here:
https://nuwavemarine.com/special-ord...ermo-849927t1/

I also just remembered Speedy buying some aftermarket replacements for his 500EFI’s. Maybe he’ll chime in. If not, send’m a pm.

exactly why you need to buy a used one

Something weird going on here. Put thermostat back in, boat would not even turn over. Turn Key and then move shifter slowly until engines turns over and it starts right up and run great like the starboard... not loud, but then about 60 seconds into, it runs harder and starts stuter unless manually controlling, then I hear the IAC kick on, and just runs rough and when more gas is applied it stutters until more gas then it jumps up to 2200 rpms and runs rough... I have had mechnic out with computer, they do not know.... replaced IAC last year tons of sensors... spark plugs, distributor cap, etc..

Compression test, fuel pressure test, and a look at the plugs....may have something going on in the valve train or a bad hole causing havoc in the computer trying to compensate for it?