Hi,

I was out boating for the last couple of days with no problems. Then yesterday I ran my engines (merc 454 carb 330s) up to 3200 for about 2 mins when my starboard temp gauge siren went off. I shut it down & limped home on port motor. I run FWC units on both motors with merc HP 500 style manifolds & stainless risers + y-pipes diverters. I use the standard raw water pumps on both. When I got the boat back on the trailer (one engine & no power steering) & flushed both motors, the starboard motor seems to pump raw water fine. The coolant levels are fine also. Both drives are clear & free of debris. Before pulling the raw water pump, could it be a blockage in the FWC system??

Yes, If you don't have strainers debris will collect in the first cooler in the flow route. Heat exchangers generally have small cross tubes. Try to back flush and see what comes out . Some heat exchangers have end caps making inspection easy.

Thanks Mobile. Mine are the San Juan type. Are these easy to access & backflush? What is the procedure??

I'm can't say what access you may have but, after you figure your direction of flow you can remove hoses and reverse flow with a garden hose through the cooler to back flush. I would suggest one at a time and pay attention to what if anything comes out. In some cases you can look in the end and see the ends of the tubes inside the cooler.

Ok. Is there a chance that debris could be caught inside engine cooling passages?

The engine side is separate; I guess its possible engine scaling may have built up and caused clog. Were they always FWC or was it added recently. If flow is good and even side to side on a hose maybe your thermostat hung up? Did a flush cap allow air in coolant line? If impeller has two seasons on it change them. I can only guess.

I always tend to get more water expelled through one exhaust tip than the other. Temps on both pipes feel similar however. The FWC was added at about 250 hrs. 220 of those were fresh water use.

What do you mean by a flush cap?? I only replaced the impellers less than a year ago.

I would top off my engine antifreeze level and make sure the overflow tanks are at the correct level. Then run it again. I would suspect an air pocket developed and wouldnt allow the tstat to open. Drilling small holes in the tstats help prevent this problem by letting the steam pass. I would also wonder if it needs to be topped off, why. You should pressure test the coolant system if so.

BT

Ok thanks Blue Thunder. My overflows generally are pretty dry when cold but I thought that was normal. The heat exchanger is full. When hot, the expansion should push coolant into the reservoir?? Then suck back during cool down??