gm 305 79-82(mcm 228) overheating

[sarantis]

May somebody who is absolutely sure tell me if the gasket between exhaust manifold and elbow for seawater cooling system(raw water) has water passages?
Here is the manifold and the elbow is the one at the left.My engine has the thermostat with the 8 hoses :
http://www.sterndrive.info/sterndriveparts/manifold_gm_305_350_1977_1982.html

 

[Don S]

Re: gm 305 79-82(mcm 228) overheating

The (OEM) gaskets all have the holes in them. But, you do have to use the seperator plate between them. So you will need 4 gaskets and 2 seperator plates.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

So you tell me that at this engine there is no water flowing from the manifolds directly to the elbows?

 

[Don S]

Re: gm 305 79-82(mcm 228) overheating

That's it, here is the cooling system diagram that shows how it's setup.
Just a link because of size.

http://i123.photobucket.com/albums/o291/DonSind/228cooling.png

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

You are so ...I can't find words to describe your contribution to my Knowledge!I think i just found why my poor motor is not going over 3000rpm 2 years now.

 

[Don S]

Re: gm 305 79-82(mcm 228) overheating

The type riser gaskets isn't going to keep the engine from going over 3000 rpm.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

Ok,not exactly 3000rpm.I was reaching about 3700 and then misfiring.I 'll try the new gaskets and then i 'll report the results.Thanks once again.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

Don S are you sure about your reply? Because the service manual i had has exactly the same diagram but under theseparation plate has the notice : (vented) which i think it means with openings.Anyway i put the knew gaskets as you suggestd and now the engine runs hoter than previously.i asked my dealer and told me that i should use one gasket ,the one with the openings and the one without them is for the closed cooling system.Your suggestion was according to theory or you have met this occasion in practice?
Nobody in this forum has a gm 305 79-82

 

[Don S]

Re: gm 305 79-82(mcm 228) overheating

I am only as sure as the Mercruiser manuals and parts manual.
The "Vented" means it should have a small 1/8" hole in one of the water passages. Only used for draining when engine is not running. When running, the plate blocks off the manifold from the riser.
Now I don't know what else you have wrong, but if you put in the proper OEM parts and it overheated, then something else is wrong.
Here is a picture from the Merc parts manual, the numers are supperceded, which doesn't show here. But the quantities are correct. There is NO WAY you can have a SS plate in there with only one gasket, that plate needs a gasket on both sides.

http://i123.photobucket.com/albums/o291/DonSind/228exhaustmanifoldandriser.png


The new PN for the gaskets are 997772, plate stays the same.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

ok thanks,i'' ll keep searching.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

The bad choice of gaskets between manifold-elbow didn't allow the water to come up and that's why i've replaced 4 times the intake manifold gasket and each time after some minutes of runing at wot the intake manifold overheated,smoke at the crossover point and water leak at the water passages.Now i wonder if the head gaskets and the heads have baeen intact from the overhaeting and i want to try another pair of intake gaskets .But this time i intend to cut my own gaskets.Will bakelite with or without internal metal strings is OK?I've used it in the past for the exhaust manifolds and between elbow-ex.manifold and had no problem.What do you suggest Don S?

 

[Don S]

Re: gm 305 79-82(mcm 228) overheating

What do you suggest Don S?

I think if you quit "Making" things and trying quick fixes, and purchaces the proper gaskets and materials for the job, put it together "By The BOOK". that it would probably work like it's supposed to.

 

[Uraijit]

Re: gm 305 79-82(mcm 228) overheating

Not to contradict Don S' vast knowledge here, but I've twice used my own homemade gaskets, out of some blue Fel-Pro gasket material. It's about $6 per roll at autozone.

Hell, my manual even has a template for the gaskets!

The local marina wanted $17 per gasket set, and wanted me to wait 15 days. So I told 'em no thanks, and went to autozone, and picked up a roll of the rubberized gasket material.

Took the separator plate, and used it as a stencil to mark out the layout of the gaskets. Used a razor blade (x-acto knife would work better), and a pair of scissors to cut them out. Once I had 4 gaskets the same shape as the plates, I used the razor blade to cut the vent holes in the gaskets. No need to cut out the water jacket openings, since they're blocked by the plate anyway, and will, more than likely, be another possible source for leaks.

Anyway, it worked great. No leaks, and I'm running at the bottom of the "green zone" on my temp gauge.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

i 've bad news and now it's neccessary.I connected 2 clear plastic hoses from exhausts' outlet to the therm. housing and when i rev it up the hoses fill with exhaust air bubles so i went on and took out the heads.Untightening the head bolts i noticed that at both sides aft (#7 and #8 cylinders) it was slightly easier to untigthen.And when i pulled the heads ...water came out from the last exhaust ports (at cylinders #7 and #8 )from both heads.It's obvious that exhaust was passing through the cooling system and vice versa .The head gaskets looked ok and the cylinders were looking ok with the notice that #7 and #8 were not lubricated ,logical since water was washing the walls.(At low RPM i had occasionally about every 3-5 seconds very little bubbles at the cooling system).I 've never had water in oil. Oil pressure is good.
And now a few things about its history.The previous owner had told me that after a damaged impeller and overheating he replaced the head gaskets (without using dynamometer wrench)and planned the heads.But the engine kept working in higher temperatures possibly because he made a mistake and while changing the ex. manifolds didn't use the right gaskets(he put only the one with the openings so the water didn't come up to cool the intake manifold and the heads).That's why when i bought it i had exhaust fumes out of the crossover point and generally even with a new gasket the intake was
leaking when trying t go at wot.I do not trust having the heads rebuilt and i intend to replace them with new ones but i wonder if something else inside the block caused overheating e.g. an oil or water passage common to both aft cylinders.In this case i'll spent 1200$ and again i will fishing from the dock!
In some minutes i'll send pictures.

 

[CharlieB]

Re: gm 305 79-82(mcm 228) overheating

Don is correct about those little holes NEED TO BE in those block off plates.

The reason is two-fold, not just to drain the risers when not running, but most importantly to vent any steam from the exhaust manifold water jacket during operation.

Without those little holes you risk COOKING your exhaust manifolds as they will NOT FILL COMPLETELY with water.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

Here are the photos.The scratches at the piston were by my finger .A car mechanic that looked the heads told me that all cylinders apart from the obvious 7-8 worked with salt water.
Thanks in advance for experts' estimation.

 

[sarantis]

Re: gm 305 79-82(mcm 228) overheating

Charlie B, thanks very useful information but what i'm doing now? Do you suspect any damage to the block?