Merc 1075 Overheating
 

My stbd engine is overheating in high RPM only. In Idle its fine it could run all day at about 150. I just replaced all 3 impellers in the raw water pump and im getting great water pressure but it still gets hot when running hard. I'm guesssing I probably have some seaweed or sand that passed through the strainers. Anyone experienced this and had good results?

Maybe backflushing the system? Possibly inside the oil cooler? What would be the easiest way to backflush the system where to start and finish? Or any other suggestions.

One this engine, did you manage to destroy the impeller or did you just change it due to the over heat problem? Do you have water pressure gauges? It definetly sounds like a restriction issue... oil cooler is where I would look especially if you lost an impeller... Good Luck

Todd

Does that motor have a power steering cooler?

teamsynergy,
No the impeller came out perfect they were just already bent to position and getting hard when inspected also stamped 08'. I have smartcraft vessel view race edition and analog gauges water preassure is even on both engines at high RPM I beleave somehwere in the rage of 20-25psi. To flush the oil cooler do I need to pull the raw water pump out to get to the inlet hose or is there an easier way?

JoeD,
Not sure on the power steering cooler I dont think it does.

if you have equal water pressure and the overheating is at high RPM sounds like it's leaning out driving temps up..

If your engines were working fine before you changed the water pump impellers, then you may have torn and broke off your new ones. Sometimes it takes a while to prime your water pump after new impellers are installed. If this is not done correctly, you can destory your new impellers. After you changed your impellers, did you start your engines in the water for the first time or on the trailer with a water hose. Hopefully you have a seperate water hose connection on your boat and you do not have to rely on those water clamps that attach to your stern drive. If you started up your motor in the water for the first time and left it at idle, you may not had enough RPM to prime your water pump. Result is broken impeller blades.

The Mercury maintence book that came with your engines gives you step by step procedures for flushing coolers. That seagrass is a ***** !!

Might check the seals on your strainers too. If the rubber gasket around the top is not sealing properly, you can pull air into the system which reduces cooling efficiency. At low RPM's the suction from the raw water pumps isn't much so it stays cool, but at higher RPM's those pumps really start sucking and could be pulling air in. Just another thought.

In the maintenance manual it shows how to clean the transmission/ power steering cooler. Could this be part of the over heat or just the oil coolers. I just got my service manual for my engines and it looks like I would have to drain the oil in the lines and bellhousing to access the oil coolers. Any one can help bbefore I go on this mission and find out I didnt have to. In the trouble shooting guide it says to check charge air cooler for foreign material, would I have to pull off superchargers to get to that cooler? Also I checked the seals around strainers and there perfect. Its annoying I can run the boat all day as long as I dont push it hard. I know it has to have some seaweed its running around 10-12 degrees hotter than the other at any given speed.

A couple of other possibilities, are you pulling water thru the outdrives? I had a similiar overheat, caused by the hose fitting on the intermediated housing. It became corroded with salt around the inside of the fitting , causing the hose to close down, to approximately 1/8 of an inch , no problem at idle but once up above 3500 temp starts to creep up. Could not figure it out until I was hanging off of the transome and noticed I was getting less water out of the exhaust, from the motor that was running hot.
Are your guages both accurate?
Good luck post your findings, so we all know what the cause was.