OMC Riser replacement

[jmarine225]

I have a 93 Four winns Vista with an omc 5.8. I went through all the trouble shooting for overheat issues and am still running hotter than normal as I cannot touch the risers for long when the engine is running--showing temps around 180 and have a 160 t-stat. It appears the original exhaust manifolds are on the engine and one of the risers is original. The boat has been used in brackage-brine water also. I am looking to replace the risers to see if that helps with temp. I reviewed the manual and it appears to be an easy job, removing 4 bolts and the exhaust hose. My question is can I complete the riser replacement while the boat is still on the water? I can't see why not since water doesn't come up that high and I have no water in my oil. Please help ASAP as I'm looking to replace these this weekend. Thanks.

 

[P 0 P E Y E]

Re: OMC Riser replacement

Other than the exhaust risers being hot to the touch, are there any other symptoms?

Touching exhaust parts on any engine should feel hot to the touch.

180' fwc engine, no alarms, no hoses being blown off, no paint turning brown...you may be able to finish the season and make the call.

 

[jmarine225]

Re: OMC Riser replacement

Well I already blew an exhaust hose and the mechanic said he found the problem---parts of an old impeller in the power steering cooler. It seems to be running just a bit hotter than normal and I figured I should change them for the small amount of money. It has a 160 t-stat but temp goes up to the 170-180 range and drops back down. I keep getting different opinions on the site if there is a problem or not. Someone posted you should be able to keep your hands on the risers while the engine is running. I could do that for about 5 seconds and thats it. This is the final step on my checklist for the overheating issue----if there even is one.

 

[rs2k]

Re: OMC Riser replacement

It is completely normal for an older (read as corroded) marine engine to run 20? hotter than the t-stat opening temp. A newer or less corroded engine should run 0? - 10? hotter than the t-stats opening temperature. 160? is just the opening temperature. It's not fully open until 20? later.

On my old electric stringer the intake water from the impeller goes into the exhaust manifold first, then it goes to the engine and then back to the manifolds. Those manifolds run cool to the touch but I do not belive this is a normal setup. I believe the previous owner used the closed cooling ports on the manifold to make it run cooler.

On my newer OMC stringers (the exhaust system is similar to the cobra) the impeller intake runs to the t-stat housing which splits to the engine first if needed, then to the exhaust manifolds. If the engine t-stat is closed the water will go directly to the exhaust manifolds. Those manifolds run warm at first and then hot... way too hot for me to touch for more than a few seconds.

The newer stringers run 155?-180? depending on how much load they are under with a 160? t-stat. If I keep the boat struggling in the hole for a while they tend to go up to 180?. If I idle they run around 155?. If I am cruising they run around 170?. If I shut down the engines without letting them cool after running them hard they go upwards of 190? - 200? while sitting. This is normal (but not good as it can cause scaling) as the heat in the engines has to go somewhere. It's best to let the engine cool down after running it hard.


It sounds to me like your engine is operating normally.

 

[jmarine225]

Re: OMC Riser replacement

Thanks for your help. The only other question then is what should the max temp be off the risers? I have an IR gun. And at what temp will an exhaust hose blow?

 

[rs2k]

Re: OMC Riser replacement

They will be at least the same temperature as the engine coolant. They will most likely be 10? - 20? above that because of the exhaust manifold they are cooling.

 

[bruceb58]

Re: OMC Riser replacement

The risers will get warm for 2 reasons...not enough water reaching them because of low flow before the riser or low flow caused by the riser itself. You have not determined which that to be so you may be replacing your riser prematurely. Best to take it off and then make that determination.

 

[jmarine225]

Re: OMC Riser replacement

ok. so if my engine is running at 160-170 then it would be normal for my riser temp to be roughing 180-190? What temp is too hot for the risers?

 

[rs2k]

Re: OMC Riser replacement

i don't think it should ever go above 190? as the rubber exhaust components won't last long above that temp.

Coast guard regulations say nothing in the engine compartment should ever exceed 200?

 

[Gary H NC]

Re: OMC Riser replacement

16 year old manifolds and brackish water?.....might just be time to replace all of them. If they are original i am amazed they lasted that long.

 

[jmarine225]

Re: OMC Riser replacement

Yeah I figured as much about the manifolds. They are probably the originals on the boat as they are stamped OMC on the sides of them. As for the risers they have been changed and are aftermarket. Sounds like a job i'll attempt in a few weeks off the water. Thanks for the help.