Hot Risers

[kwoolard]

Helping a friend of mine with his new engine break in. We installed his new 350 from Michigan Motorz and got the timing set and engine running good. Engine is raw water cooled. We noticed that the risers were getting pretty hot on the muffs, water was flowing out the relief ports and the prop but the water was extremely hot. Checked various points around the engine with temp gun. Engine temp is steady at 160, but the risers were 150 as well as the exhaust manifolds.

We decided to run it in the water thinking the water hose just wasn't providing good flow and got the same results. Continued running varying the rpms up to 2000 for the break in and shot the engine with the IR gun to get some temp readings. Engine temp still steady at 160 but both risers crept up to 190, the port manifold was 145 and the starboard manifold was 175. These temps stayed steady no matter how long we ran the motor.

There are no kinked hoses, new t-stat and manifolds and risers are clean and only a couple of years old with very little use. I read on some other posts here that the riser gaskets could be a problem. The t-stat housing is the one from a 1999 5.7L RWC set up that dumps the water into the bottom of the exhaust manifold and flows into the riser from there and out the exhaust. The riser gaskets that we've got installed now are the restricted gaskets, with 2 slots and 2 holes, but from what I read he should have the 4 slot gaskets.

Would the 4 slot gaskets provide that much more cooling versus the 2 slot with the holes? We are going to install the 4 slot gaskets tomorrow and retest.

Could this be a lean burn causing the exhaust temperature to be hot? We're going to check the plugs tomorrow and see if they are white.

 

[Alpheus]

Re: Hot Risers

Are you running new manifolds and risers?

Engine temps at the core is what I would worry about and you said its at a steady 160...

 

[BAproject]

Re: Hot Risers

core is important but risers should not be getting that hot...it seems like restricted water flow somewhere.

Salt water? You said the manifolds and risers were a couple of years old, if you run in salt water and don;t flush out after every use then the lifespan of the risers is not very long.....I would think about replacing them....

Is there enough water getting to the engine to feed the circ pump and exhaust stack, i.e. impeller, clogged feeder hose?

 

[kwoolard]

Re: Hot Risers

Yeah the engine temp is good, confirmed by the gauge and the IR temp gun. Checked the temp at the t-stat housing, temp sender, and all the core plugs I could access. Temp is at a steady 160.

The manifolds and risers are not new but in good condition. We've had them off and flushed them out and they all had good flow through them. I was just wondering if those gaskets could restrict the water flow that much.

I'm also concerned about the the hot exhaust burning the rubber components in the exhaust system.

 

[HT32BSX115]

Re: Hot Risers

Howdy,


I would NEVER use "used but good" manifolds and risers on a "new" engine.


Your only saving about $500 bucks by not buying a new manifold-riser kit.

I also didn't see any thing about replacing the raw water pump and ensuring the raw water circuit from the drive to the t-stat is absolutely clear of obstructions.

 

[kwoolard]

Re: Hot Risers

We haven't measured the water flow, but the water pump in the outdrive was replaced last year and it probably has 20 hrs on it.

What is the flow spec on an Alpha One water pump? I think I've read somewhere 15gpm for an Alpha Gen II, but don't know about the smaller water pump in the Alpha One.

 

[jerryjerry05]

Re: Hot Risers

You can't just flush a riser/manifold.What year is the setup?? If the riser/ manifold is older than 10 years and it's been used in salt water then you probably need new.If you put the wrong gasket in it will overheat also.
Make sure the holes are free and able to flow.The T-stat housing sounds like it might be wrong too.Why the change from the original?
Dont skimp and cook a new motor.Change the waterpump impeller and wear plates.J

 

[kwoolard]

Re: Hot Risers

the manifolds and risers are 2 years old and only have about 20 hrs on them, so practically they are new.

it turned out to be the hose between the bell housing and transom assembly. when the drive was lowered into the running position the 3/4" hose had a weak spot and was kinking almost closed.

 

[alien4fish]

Re: Hot Risers

im having the same issue, new impellar, new water pump and it is still heating up when i run it at 2500-3000 trying to break her in, but when i got off the throttle it would cool back down kinked hose between bell housing and transom huh? Hmmm........... I will be checking into that today!
Thanks for posting what you found!

 

[HT32BSX115]

Re: Hot Risers

the manifolds and risers are 2 years old and only have about 20 hrs on them, so practically they are new.

That would probably be true!

it turned out to be the hose between the bell housing and transom assembly. when the drive was lowered into the running position the 3/4" hose had a weak spot and was kinking almost closed.

That'll do it every time!!

Glad you found the problem!!

 

[kwoolard]

Re: Hot Risers

Back with another question regarding the hot riser issue.

The 3/4" hose has been replaced between the bell housing and the transom, which was 1" too long and kinked every time the drive was lowered. however, the risers are still getting up to 150 degree F or so running the boat on the muffs. Haven't taken it out yet to see if anything changes while under way, but we don't think the risers should be getting that warm.

This drive is the Alpha 1 drive with the smaller water pump. When we put the new motor in we changed the thermostat housing from the one with the spring loaded balls to the one without them(came off a 1999 merc alpha gen II). We are just wondering if the newer t-stat housing is causing this hot riser condition when used with the Alpha 1 water pump? That is the only thing different between the old and new motor, obviously we had to re-route the hoses different with the newer t-stat housing.

Just to rule it out, the water pump in the outdrive is being changed, a picture of the old one (which is only a year old) is attached.

 

[Brentathon]

Re: Hot Risers

That impeller doesn't look so good.....the vanes seem to have taken quite a bit of "set". I just went through a whole ordeal with a new (yet defective) impeller, that had stiff rubber and the vanes took a set. My theory, is that if they take a set, they fail to continuously contact the casing throught the entire revolution....especially at higher rpm's.

I posted pics of my impeller comparisons in a previous posting.