high speed over heating FWC
 

Hello, I have a high speed over heating issue with a my 1996 7.4 LX with Fresh water cooling.

This overheating is a result of running aground on a sandbar. Prior to running aground everything with perfect. Cooling was at 160 all day long. So to try and remedy this issue I pulled the sea water pump and changed the impeller and 1 piece housing. Additionally, I removed all the hoses after the pump up to the riser. I found most of the impeller pieces at the oil cooler, which has a honeycomb style that trapped all the pieces. After the oil cooler I flushed and inspected, cleaned the heat ex-changer. This was clear of any debris. I finally removed the hoses to the rise and this clear. Additionally I back flushed from the sea pump to the outdrive for several minutes removing sand from the outdrive.
I took the boat back out and noticed everything to be fine at slow speed but at approximately 2000 RPM I see the temperature rise to 180 and stay there. I continued on at the same speed for about 30 minutes and did not see a increase but only at 2000 rpm. I then headed back as this did not seem normal.
The only thing I am questionable about is the inlet / outlet of the sea pump. I am getting mixed information when researching on the web regarding this.

The pump is mounted on the starboard side with a standard rotation. I am now questioning everything and wondering if I might have mixed up the inlet and outlet on the pump.

Any suggestions?

Thanks

The cooling system would not work at all, if you mixed up the hoses.

Your high percentage issues would be . . .

Still clogged somewhere . . Hoses, coolers or heat exchanger. Do you have sea water strainers on the engine?

The impeller got worn down with the sand and now is not pulling as much water in as it should.

I only have the alpha and my problem was at idle, my problem was at the transom were the water came in plastic tube was crushing in, restricting the flow. I would check to see if you have any restriction.

Do you have a fresh water hose connection going into the sea-water side of the cooling system? (For flushing with a hose after salt water boating)

If so, I have seen some of those kits that have check ball systems in them. The check ball systems get gummed up with sand/weeds/debris and restrict flow. They run enough pressure for sufficient cooling at low speeds, but the restriction becomes an issue at higher speed as the cooling water coming in can't keep up.

Thanks guys for the responses.

Tpenfield,
I doubt there is still a clogg but I will leave no stone unturned again. I will pull all the hose as I replaced them with new ones, just because I had them off. Also what you mentioned regarding the impeller, I will check again. Thanks

Masi242,

I back flushed the system and pushed the water hose all the way to the plastic inlet piece and had what I think is good flow out of the out drive. I can put a link on you tube for you and others to see to comment.
Thanks

Sydways,
I do have one it is a perko with the check valve / balls as you mentioned, I too this unit out when I was back flushing and clean it out.
Also I do not have a sea strainer but have one on order to install. I will not install it until I get this under control.
Links to back flushing
http://m.youtube.com/watch?v=_XLEiqRxNVI

http://m.youtube.com/watch?v=qxXSKHOleE4

Sounds very similar to what was happening to my buddy's brand new Baja years ago. Make sure that ball is moving freely.
Actually, you can take it out. It's not needed as long as you have a solid cap on the end of the hose line that won't leak air. It's more liability.

Priobe -

Looks like typo in my original post. . . .

the sand that you sucked into the cooling system could have caused damage (or wear) to the impeller in the sea water pump. therefore it would not be as effective.

He already changed it.

Correct, I already changed the impeller on the sea pump. I plan on taking it apart again to inspect the impeller again.

Also I plan on inspecting the rwc system again.

Another question I have is although it is fwc, there is sea water that passes to the risers. Should I remove the risers and inspect them? I understand the manifolds are fresh water but the risers may have sand in the, is that possible?

This has got me stumped

I had a similar problem once and it ended up being that some of the honeycomb channels in the oil cooler were clogged with sand/dirt from the sandbar. There were enough channels open to be ok at idle or very low rpm, but as soon as you started getting the rpm up it would start to over heat. The debris had hardened so much that it would not flush out. Had to take the oil cooler off and boil it to get it cleaned out.