5.7 mercruiser bench test starboard riser hotter than port

[84EdH]

I am running my fresh 5.7 longblock set up on the engine stand. It is a mercruiser 1995 setup using centerrise manifolds, thermostat housing, etc. all is well but for two issues:


1) I see the starboard side of engine water flow out the exhaust is less than port, the riser on the starboard is hotter than port. I can put my hand on the port side riser and leave it, the starboard I can grab it, but not for long.......is this bad? how to fix?

2) tiny(just a drip)of water from one of the manifolds to the brass elbow fitting on the bottom of the manifold......I have tape on it, and I am a little worried about turning it in another 360 degrees. what is the proper thread coating for this fitting?

thanks

 

[krisnowicki]

Re: 5.7 mercruiser bench test starboard riser hotter than port

As Don S says "teflon tape has no place on a boat" I use pipe dope for everything.. . the riser temperature thing is normal. The water takes the path of least resistance so as long as it isn't hot it will be fine.

 

[poor boater]

Re: 5.7 mercruiser bench test starboard riser hotter than port

are you using old manifolds and have you removed drain valve or looked into water passages to make sure there is nothing blocking flow

 

[84EdH]

Re: 5.7 mercruiser bench test starboard riser hotter than port

Kris, how do I know how hot "too hot" is ?

pb.....manifolds are almost new.....checked thoroughly while off the engine...new drain valves also.

 

[poor boater]

Re: 5.7 mercruiser bench test starboard riser hotter than port

merc says 160 max

 

[84EdH]

Re: 5.7 mercruiser bench test starboard riser hotter than port

160 max.......do think that applys to the risers also?

 

[mancho]

Re: 5.7 mercruiser bench test starboard riser hotter than port

Just to toss this in, I have noticed exactly the same thing in my 5.7L 1998 engine. Well, the engine might be a year or so earlier. I haven't ran my serial numbers to check exactly the year of the engine.

I have 4 inch thru hull exhausts and my starboard is hot after engine gets warmed up but the port side stays cool... well, relatively. it's warm from the engine heat but about 15 to 20 degrees cooler than the starboard. I am measuring exhaust water, not on the riser, but at the pipe.

 

[poor boater]

Re: 5.7 mercruiser bench test starboard riser hotter than port

yes the local merc shop that is at the elbow... hope it helps

 

[84EdH]

Re: 5.7 mercruiser bench test starboard riser hotter than port

i'll see if I can sneak my wifes oven thermometer out to the barn and see what temps I get.......

thanks!

 

[Rideau River Rat]

Re: 5.7 mercruiser bench test starboard riser hotter than port

I spent 2 weeks trouble shooting the exact same thing. Called Mercruiser, got the "It's normal"?. But the heat on the SB side was too hot for me to ignore. My newly rebuilt 5.7 had everything replaced except for the water circ pump on the engine. I ordered a new one from Sierra and while I waited for it to arrive I removed the old and took it apart. Nothing to loose at this point. Easy to take apart - remove the back plate and pound out the shaft to get a look at the vane side of the steel impeller. Impeller was not broke but it had a fair bit of growth with some interesting artistic formations. So I grinded/wire wheeled the crusty impeller and reassembled the circ pump. Since I had time before the new pump arrived I decided to reinstall it and give it a go. As soon as I started the engine with the now leaking, BUT clean/smooth impeller circ pump, I knew there was going to be good news. The sound I previously heard around the water circ pump area was gone. The engine came up to proper temp and the Starboard header side was just slightly warmer then the port. Now I'll agree with Mercruiser on that one. Next day the new circ pump arrived and in NASCAR style I had the old one off, new one on in no time. The sound I previously heard with the old pump was cavitations bubbles caused by the messy surface of the circ pump impeller. Air in the block and then to the thermostat housing was the problem. Had the boat out all week and all is well.