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Exhaust manifold hot spot

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ralphs

New member
I have 1985 454 model 350 engines FWC. Around 700 hours.
Stbd engine was running 15-20 degrees hotter than port engine. I replaced the raw water impeller (found one torn vane) and U-Cooler, and that helped, now running 10-15 degrees hotter. I used my IR gun to check various temps and found that the hottest spot (top rear near the water discharge connection) on one exhaust manifold was 200 while the same spot on the other manifold was 190. This measurement was taken at the dock running about 1500 rpm. Is this normal? Should I suspect a blockage in the manifold and tear it apart? I believe the manifolds are original, but the risers have been replaced. I also see a bit more steam (and soot) from the starboard engine at cruise. My domestic water heater is conected to the port engine.

Thanks!
 
A manifold blockage would be unusual, the passages are very big. The steam is a good indicator of too little raw water flow. The best single point measurement of the engine temp is at the thermostat housing; mid 160's is normal at cruise. Measurements at the dock are of little value. With new risers and U cooler, I'd take a look at the cam and cover of the raw water pump.
 
I recently burned through an exhaust hose on my Tiara 3100 with Crusader 454 engines and after reading some of the threads on this subject I purchased an IR therometer and checked the temperatures of the manifolds, Risers and elbows. With the boat idling at the dock and after reaching operating temperature i found the following
Port Engine:
Manifold 258 degrees on hull side. 206 degress on other side.
Riser:230 degrees on hull side. 110 on other side.
Exhaut Elbow:307 degrees on hull side. 98 degrees on other side.

Starboard Engine
Manifold 196 degrees on hull side. 190 degress on other side.
Riser: 130 degrees on hull side. 120 degrees on other side.
Elbow: 215 degrees on hull side. 108 on other side.

I am planning on replacing the risers and elbows but I am hoping not to have to change the manifolds as access is a real issue on this boat. However the temperature readings on the manifolds seems to be higher than they should be based on what I have read on this forum. My question is whether changing the risers and elbows might also help lower the manifold temperature. Lastly, I also checked the temperature at the thermostat housing and got 187 degrees on the Port side but 163 degrees at Starboard. Any input is greatly appreciated.
Thanks
 
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You burned thru an exhaust hose, but did you replace anything besides the hose? It appears you have a clogged riser or elbow. Nothing is normal with a >200 degree exterior wet cooling system.
 
Dave,
Thanks for the quick response. My post was not complete when I accidently hit the "send" button. The corrected post containing bettter information is now present.
Thanks
 
If the riser/elbow is restricted, it limits the raw water flow which reduces the amount of heat removed from the closed side. The end result is elevated engine coolant temperature and eventual overheat. The reduced raw water flow also reduces the cooling effect provided to the hoses connected to the elbows. As you've found out, burnt hoses are the typical end result. I've seen exhaust hoses become useless is less than a minute when the raw water flow is cut back.

I'd say a complete riser/elbow replacement is a prudent first step.
 
Mark,
Thanks for the advice. I ordered new risers and elbows today for one of the motors and will be installing as soon as i get them. If installation on this motor goes well, I will proceed to the other one.
 
Depending on the year of your engines and their water circulation, watch out for the gasket type and placement.....yup, don't ask
 
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