Hot Risers

[sharkmtn1]

My Osco risers and manifolds are getting way too hot. The engine's temp is normal and I checked and replaced the impellor and I'm still having problems. A friend of mine said Osco's run warmer than other brands. I'm not sure I believe that.

 

[Don S]

Re: Hot Risers

What are we working on here? OMC, Volvo, Mercruiser, V8, 4 cyl, what drive and year and all that good stuff.

 

[sharkmtn1]

Re: Hot Risers

Sorry. It's a 1984 2 PC rear main seal, 4 bolt main Mercruiser 5.7L engine (carb) that I just purchased brand new and installed this summer. It's got an aftermarket equivalent Alpha One Gen One.

 

[Don S]

Re: Hot Risers

Is this how your system is setup? or do you have a closed cooling system, different type manifolds and risers, etc.

 

[sharkmtn1]

Re: Hot Risers

Raw water cooled center style 3"Osco risers and manifolds. Also, have thru hull exhaust. Thanks for the quick reply by the way. I wish my husband was that fast.

 

[Don S]

Re: Hot Risers

Can you post a picture of the engine? Need to see the hose routing and thermostat housing of your setup. It's obviously been changed to the new style manifolds and riseers, guess it's time to make sure the hose routing is correct.

 

[sharkmtn1]

Re: Hot Risers

Sure. It will take me just a minute.

 

[sharkmtn1]

Re: Hot Risers

Here are pics.

 

[Don S]

Re: Hot Risers

Since I haven't seen a thermostat housing like that before, I can't really comment on it being plumbed correctly or not. Are you sure the correct gaskets are used between the manifold and riser? as recommended by Osco.

One other note from the pictures, that type distributor is not a marine distributor, unless there is an aftermarket company for that type distributor that makes them for marine.
If automotive, it would not only not be spark protected, but probably have the wrong advance characteristics as well.
I assume the carb and fuel pump is also marine and not automotive!

 

[wire2]

Re: Hot Risers

.....
I assume the carb and fuel pump is also marine and not automotive!

There's a clear hose beside the black inlet hose (not metal?) showing in pic 1

 

[sharkmtn1]

Re: Hot Risers

I know the tstat looks odd but it's correct. As for the clear line, it is from the fuel pump incase the diaphram fails, so I don't end up with a bilge full of gas vapors. The distributor, I had to modify in order for it to be CG approved. I first had to remove the vacuum advance and seal the hole. Then I had to drill a new hole and tap in a brass washer then a brass screen, then another washer. As for the advance, all that was done was repostion the stop bushing in relation to the advance springs which after some minor calculating, I adjusted accordingly. I also had the engine shipped with the manifoldsand risers off so I could port the manifolds. It adds a little more power. And yes, the correct gasket were used. Not bad for a girl.

 

[Danny Mc]

Re: Hot Risers

What kind of flame arrestor and throttle bracket are they? I am lookin for them for a carb change. D Mc

 

[Dshow]

Re: Hot Risers

No sure what she said, but I'm impressed... I think...

 

[keelhauled]

Re: Hot Risers

This is a stab on the dark, but Don S might be on to something with the HEI distributor. Is your timing retarding or too retarded causing heat build up in the exhaust?

I'm thinking you are getting more than adequate raw water to your engine to keep your block temp normal but the heat is being carried out by the water which is piping hot by the time it reaches the riser?

I'm probably way off but I wanted to have a guess too

 

[sharkmtn1]

Re: Hot Risers

What kind of flame arrestor and throttle bracket are they? I am lookin for them for a carb change. D Mc

The flame arrestor is a Mallory with the offset hole but the throttle bracket is something I made out of almuminum.

 

[commander315]

Re: Hot Risers

This is a stab on the dark, but Don S might be on to something with the HEI distributor. Is your timing retarding or too retarded causing heat build up in the exhaust?

I'm thinking you are getting more than adequate raw water to your engine to keep your block temp normal but the heat is being carried out by the water which is piping hot by the time it reaches the riser?

I'm probably way off but I wanted to have a guess too

I have the same Osco set up on both my motor and never had a problem. I agree with what keelhauled said about the timing and the second part about the raw water. I heard of a similar situation in which the block stayed cool but all the heat was soaked up in the exhaust.
One other thing, if you have a way of taking the temp of the risers and manifolds, that would be good for reference. (One of those infrared thermometer thingys would be great)