Riser Temperatures

[carolynrose]

1988 OMC Cobra 5.7, last year I replaced the old log style factory manifolds and risers with OSCO centerise 3'' exhaust. I thought the engine lost a little power so this year I switched the risers to 4". The power did seem to come up a little and the engine temperature definitely dropped a few degrees.

My question is about what temperature should the risers be when running hard for a while. At idle I can rest my hands on the risers all day long, there somewhat warm but bearable. I checked them while my buddy was running hard and they were definetly hot. When we slowed down approaching the marina they cooled quickly to the warm touch.

I'm bringing an infrared temperature sensor to the boat this weekend and was curious to about where the temps should be. The boat has closed cooling and the manifolds and risers are the raw water side after the heat exchanger.

By the way the manifolds themselves are always much cooler than the risers, is that normal.

 

[carolynrose]

Re: Riser Temperatures

For anyone interested, I got down to the boat and checked the manifold and riser temps. Here is what I got while running 3500 rpm's for about 20 minutes. Exhaust manifolds, measured in several spots on both sides 129F - 134F. Risers on both sides around 140F, exhaust hoses and elbows after the manifolds 109F-120F. Now here is the interesting part, at the very top apex of the bend of the risers in an area of about 1 1/2" square the temp was 220F on both sides, within an inch of this spot the temperatures fell back to the 140F. I checked this several times and it was always the same. The only thing I can figure is that there is not water jacket in that area.