1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Greg68S · Feb 24, 2013

Im running a Merc 5.7 V8 in my 1989 Thompson. It runs great and at steady 160-170 degree temp regularly. But it spikes into the 200-220's when i run it wide open. It does this more often than not. My buddy suggested after my 3 thermostat changes that I look into manifolds and riser's. the previous owner did not winterize properly and there has been alot of rust build up in the water cavities. I pulled the motor today and pulled the manifolds and risers apart. they are really rusty and look pretty rough inside. Is this my problem? Can I have them dropped in a hot tank to be cleaned? or should I spend $500 dollars on a new set? I dont want to spend the money but I will if necesary. What are your thoughts?

Don S · Feb 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Sure plugged up manifolds and risers can cause your problem, you did check the impeller first didn't you? It will as well.

If your manifolds and risers are plugged up, replace them, don't just clean them out. The rust is from the manifolds and risers and is just a warning they are bad. Next step is engine replacement.

Greg68S · Feb 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Yes I replaced the impeller and housing last spring. It is all brand new. So I guess I will be replacing the Manifolds and risers. I found a kit for $499.00. Is that a good price? It includes new risers, manifolds, gaskets, and bolts.

Don S · Feb 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Greg68S said:
Yes I replaced the impeller and housing last spring. It is all brand new. So I guess I will be replacing the Manifolds and risers. I found a kit for $499.00. Is that a good price? It includes new risers, manifolds, gaskets, and bolts.

Low price yes, is it good quality for your money ????????? Probably not.

Greg68S · Feb 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

where would you suggest I buy from? The kit is put together by doug-russell marine. I believe its sierra products or mercruiser.

Greg68S · Feb 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

where would you suggest I buy from? or what manufacturer would you reccommend? I need to be as thrifty as possible with out sacrificng quality parts. The kit is put together by doug-russell marine. I believe its sierra products or mercruiser.

Greg68S · Feb 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

I just priced the manifolds and risers through iBoats. All Sierra parts $662.72 shipped.

NHGuy · Feb 25, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

I think you can get original equipment for about 20 to 30 dollars per piece more than aftermarket.I found that Doug Russell is very good on pricing when I looked up this for
myself.

agallant80 · Feb 25, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

I would check the pump again. But manifolds and risers are never a bad idea if they look that bad and like said above if they go then you can add new motor in to your repair list.

tazrig · Feb 25, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Greg68S said:
I just priced the manifolds and risers through iBoats. All Sierra parts $662.72 shipped.

I replaced my elbows with the same ones you just listed, also from iBoats. While not quite as beefy as OEM They worked fine on my 1990 5.7L's for 2 years before I sold the motors.

Greg68S · Feb 26, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Now I do have a question about cleaning. Why is it a bad idea to take my original manifolds and risers to my local machine shop and have cleaned in a dip tank? That would cost me $100.00 including new gaskets. They be like new inside and out unless they are deteriorated internally. I like the idea of new but I prefer to spend a little less money if possible and affective.

agallant80 · Feb 26, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Greg68S said:
Now I do have a question about cleaning. Why is it a bad idea to take my original manifolds and risers to my local machine shop and have cleaned in a dip tank? That would cost me $100.00 including new gaskets. They be like new inside and out unless they are deteriorated internally. I like the idea of new but I prefer to spend a little less money if possible and affective.

The manifolds are constructed to have a water jacket sourround the exhaust to cool it. If the lining of the water jacket is sarting to rust through and fails then you will put water in to your motor through the exhaust valve hydro locking the motor breaking pistons, rods etc. You will wish that you spent the $600 on the replacment parts. Your effort to save $500 could and up costing you $3,500 for new motor and what not not to mention the season you will lose to installing it or waiting for a mechanic to install the new motor. Its worth the money for the new manifolds and risers.

capecodder116 · Feb 26, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

totally agree with agallant80. Bite the bullet and do the right thing, otherwise you're asking for trouble.

Greg68S · Feb 26, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Well said. Ok. I ordered the kit through Doug Russell marine. The parts are supposed to be Mercruiser..

agallant80 · Feb 26, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

good boy

Greg68S · Mar 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Are there torque specs for the manifold bolts? I can't seem find them. From my automotive knowledge and experience there should be specs, also are there specs for the riser bolts?

Bondo · Mar 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Ayuh,... The "Spec" is 30/ 35 ft.lbs.... The typical torque for 'bout any 3/8" bolt/ nut...

I just torque 'em snug usin' my calibrated elbow...

Greg68S · Mar 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Ah! The torque wrench of common sense. That's my favorite tool. It has not failed me yet.

Greg68S · Mar 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

How about reusing the old manifold bolts? I don't foresee any issue. According to my measurements they have not stretched in the slightest.

Bondo · Mar 24, 2013

Re: 1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

Greg68S said:
How about reusing the old manifold bolts? I don't foresee any issue. According to my measurements they have not stretched in the slightest.

Ayuh,.... If they had, I'd be Shocked, 'n Amazed...

Bent, rusted, lost, or broken is 'bout the only reasons to replace 'em...

1989 Mercruiser 5.7 minor over heating problem. Manifold/riser related???

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