I have a 1973 240 srv cc with a 1975 351 mercruiser ford can any one tell me how hot manifolds should be cant touch them.took out a drain plug water burned me im hearing differnt things some are sayn manifolds should be cold others think it should be as hot as engine.temp gauge did go up into red ran it again stayed in middle please help
Dunno if this helps but my '76 SRV 300, which has the same engines, runs at 140degrees. If you have one, check the bowl from the water intake seacock, there should be a constant flow into the bowl. The strainer could be plugged up or the stainless filter in the bowl could be dirty. Or, as Niks325i sez, impeller in water pump could be shot.
If temp gauge went up into red and then returned to normal sounds like you had a clog at the intake grate down on the stern drive unit. Shutting down the engine broke the suction and cleared the clog.
Always shut down an engine if you notice an overheat problem. That kills more marine engines than anything else.
Sucking sand through the intake will abraid the rubber in the impeller and give you higher than normal idle temps. A 'take' of the rubber fins, perhaps after sitting over the winter, will deminish high speed pumping and give you hotter temps at high throttle.
Well i think i found my issue pulled manifolds and risers of found them filled 1/2 way with rust wish i would have takn a pic
got a 233 parts manual off ebay calls for a 140 thermo got that and presure washed manofolds and risers
I did find find impeller housing was a little wrarped so i replaced housing and block on bottom out drive part is done manifolds are nxt weeknd
Any1 wanna buy a boat
If they're that rusty you might want to consider replacing them. At a minimum you need to pressure test them. A leaky manifold cost me an engine. I rebuilt the engine, didn't bother testing the manifolds and it nearly bit me again. Lesson learned the hard way.