Melted rubber exhaust hose replace with stainless?
 

Got my freshened 454's running and did a high speed run that melted/blew out the black rubber hose from my EMI thunder risers to the 3" offset that attaches to the tips. I don't want to take a chance on blowing out more hose. Is the best thing to do is just pipe with stainless tubing from the riser to the offset and what's the best couplers for making the connection?

Why did it get so hot ?

Glad you asked, because I questioned it also. I have twin engines the center most exhaust hoses burned at the top. I can only think that hoses might not have been centered on risers....however the outer most hose did fine. Opinions welcomed.

Doesn't sound like there was any water going thru it.

I would check impellers just to make sure you dont cook new engines

For sure, you can always get TriDent hose also works great and comes in colors. Super easy to get on and off and has a little better look.

Really puzzling why two center most exhaust both burned. Could it be because exhaust manifolds are so close (2-3") and it gets hotter than outside manifolds? It still ought to be cool. I'm open to suggestions. Does the new cams, rocker arms increase exhaust temp? I saw 40 lbs of water pressure at 70+. at idle tho about 10psi and my sea strains weren't to the top but were swirling about 3/4 full. Any opinions welcomed.

That's a lot of pressure, could there be some kind of blockage in those manifolds or risers . Did you notice consistant water coming out of all the tailpipes.

Sounds like you are running a bit lean, which if too lean, will be hot enough to melt the hose.

After you replace the hose, make another run and check the plugs.

Are the hoses a straight shot to the tips? Any bend in the rubber hose will cause the exhaust to impact that area and really heat it up.
That is a ton of water pressure. Remember that pressure is just a measure of restriction. Just because you have a ton of pressure doesn't mean you have the volume to cool the engine. You need a happy medium of pressure and volume. I would have to good look at the entire cooling system to be sure there are no obstructions. Unless you have an MLS head gasket, you take a chance of lifting the gasket with 40 psi of pressure.
As mentioned, the Trident silicone hose is really good stuff that will handle about 100 deg more than the rubber hose. It is also pretty pricey.
You asked about more temp with new engine parts. If you are making more power than before, then more than likely you are making more heat. However, there is no reason that the rubber hose shouldn't hold up as long as there are no bends or turns in the hose.
Eddie

I ran both engines with good flow on the hose before going to the lake. Hoses burnt right at the top of the riser tails. The outer hoses are a little swollen. I don't get why inside exhaust hotter on separate engines. I could understand if same side of separate engines. Going to check the new impellers and flow water from the thermostat housing hoses and see if blockage. Just put in new merc 143 degree stats. Would it help to move the stainless 2" offset from the tips to the riser end to handle heat and pressure better? Can it be exhaust pressure building because of 2" offset at the tip and blowing the exhaust hose?

Photo of what I'm trying to solve. Opinions needed.

maybe thermostats

What was your water temp while running? Do you run crossovers?

water temp was 180-190 on a 98 degree day. i have the standard thermostat housings where water comes into housing from seapump then thermostat decides if water goes directly to manifolds or circulating pump.

My fresh air intake is on the sides directly in front of the outside risers. Think the fresh air kept the outer risers a little cooler and thats why the outer hoses did not melt, and the inner hoses did melt? it be that simple?

That might be your problem. You shouldnt be that hot, im at 140-150. I wouldnt think you would have a 180 degree thermostat. I think those are bad

Doesn't look like the offset is enough to be a consern. Could be better. Possibly welding extension to the forward end of the adapters to close up the gap, but that isn't addressing the issue. Besides, boats using silent choice or non thru hull have alot more tighter exhaust bends than yours with no problems. What do your spark plugs look like? I agree, the 40psi doesn't mean you have flow, just more in than out, (kinda). I'd be getting that down to mid 20's for safety. 10psi at idle is high, not bad, just higher than normal. Common for almost zero psi at idle. The stock Merc 2 hose t-stat housing design creates high presure in itself. The older 4 hose design with the brass tee was issue free. A relief valve will cure high pressure, but you gotta make sure you are getting enough volume out the risors first. Look closer at your plumbing. Don't see the closeness of the motors being a cause. Lack of water flow around the outer dia of your risors outlet seems likely. What was the t-stat rating when you where seeing the 180-190*?

Used brand new Merc 143 Degree in both engines. Uggh i hate to pull the plugs on the centers, but will after I check the impellers and water flow thru the risers.

Im really hoping that is all it is, that maybe I don't have good water flow around the riser tail and exhaust tubing connection.

I had the exact same problem. It's like you said above, the hose was not centered so no water was getting to it.

I changed the hose got it centered and it worked fine after that.

Have you considered putting a set of wedges between the manifolds and the risers to kick the pipes downward a little bit? That, and some of the high temp corrogated exhaust hose might solve the issue.

Maybe I'm not seeing it clearly, but the hoses look to be centered on the risors and the adapters??

If you had 143 stats and were still seeing 180-190 temps, problem isn't with the exhaust hoses. Are the outer hoses about burnt thru also? Maybe not a sign of inner exhaust issue, but just coincidence they gave out 1st?? Both motors, same problem.... T-stats installed correctly, hoses connected correctly? Just pull a couple plugs to see color.

UPDATE:
Pulled the impeller on the starboard motor, got two veins missing. Found one in the impeller housing and will look for the other piece in the morning. Going to catch my backwash of hoses and see if missing piece(s) come out. I think the builder might have cranked it dry, it has new impellers.

(on a side note, replaced my steering pumps-one went bad, idlers-one went bad, fuel/sea pump on starboard went bad. I think the previous owner must have let this boat sit in storage or no maintenance, should have just bought all new accesories for motor. trying to get the kinks out of everything. Sheez this was one trial run with all this gone bad)

Any advice or opinions to the hoses melting with this new info discovered are still welcomed by me.

Sounds like the missing pieces were or are blocking the water to the manifold or riser. You could put air through to find out. Hope you didn't cook the motors.

Going to try your suggestion of air before backwashing hopefully piece missing didn't make it pass the oil cooler and it will blow out. I started both motors when back at the boat ramp and they sounded fine, so maybe I didn't get em too hot. Kinda thinking that the rubber exhaust may have saved my motors by melting and me shutting down.

You might want to check the bolts on the manifolds and risers to see if the heat affected them, could throw a torque wrench to the head bolts while you're at it.

I would look at the feed lines for the manifolds to see if they are crushed or in any way restricting the flow.
Also, when you replaced the t-stats did or is there a white piece of plastic that was in the housing? If there was, could it be possible you installed it incorrectly and water is not getting to the exhaust on that particular side?
Something to think about.

stick your finger inside the inlet of the cooler on hte back of the block. I always find the missing peices there.

But you still had 40psi. Where is your WP gauge connected at, block drains?

Just curious, did you get any water in the boat or on the underside of the hatch from the holes in the exhaust hose.

Will check torque on bolts, check the feed lines and jumper hoses on manifolds. Builder put in stats, but I will check them. The old stats would go in only rightside up or upside down. I'm not missing a piece with the new merc stats? It was blowing a fine mist of water out burn spots. Wp taken on lower portion of block side. Hoping oil cooler caught the part, oil cooler easy to get to.

Thank you for the suggestions, it's keeping me going!

It would have to be blocked after your water pressure gauge pick up to see 40 psi.

Update on progress:
Got the starboard engine back flushed and got all the pieces of the impeller. Engine was definitely started dry, impeller housing had impeller cooked onto the inside. Flushed the risers good. Got new impeller housing and impeller installed with new sea/fuel pump.

Port engine just got the sea/fuel pump off, and haven't gotten the impeller apart yet, looked thru the hose connections and impeller looked fine but will break everything down for further inspection tomorrow. Something has got to be making the port engine hot as well.

Will also try and pull a plug or two and see color.

I would back flush the port just like you did on the starboard.

BTW

Most pick up the water pressure from the block drains, is that where your gauges hook yup to?


As for jetting did you add power when you rebuilt?

same jetting as before?

Water pressure does hook up at the blocks. Suppose to have gained around 75- 100 hp per engine with the roller cam, lifters, roller rockers, intake. Used the same merc 750 cc carbs from original 454 mags that were on engines. Engines didn't stumble when run up to 4800 rpm. What do I need to look for plug color wise to tell if run lean?

Update: Flushed all engines, pretty confident no blockages, all new impeller housings and impellers (port impellor still looked new) Started inspecting the black exhaust hose, it has all shrank in diameter cutting off the water flow around the riser tips. Ordered stainless exhaust tubing that is similar to the quick and quiet II that I removed. Thought about shooting exhaust with IR gun when completed to check exhaut or tubing temp. What tubing or exhaust temp could I see and it be acceptable (I have read 180*-500*). Am I on the right track to solving this?

Any link to where you purchased this or pictures of it? Is it flexible?

Look for 4" stainless exhaust tubing (straight runs) on jegs, ordered the rubber couplings from laboatparts on ebay.

Update: Got the rubber hose off all the risers. Each hose was touching the flared end of the riser's tail and this is where the burn thru occurred. Got one stainless piece installed between the riser and offset to the tip.

What did the riser gaskets look like

They looked fine to me, there is less than 3-4 hours on these new exhaust manifolds and risers. Is there something I need to pay attention with the gasket?

Just wondering if they were burnt and if the water holes lined up between manifold and riser.