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.

Thanks is this all great stuff.

I think I will pull the system back down again and check everything again. I know I ran a coat hanger through all the passages in the exchanger and the oil cooler, ( power steering was pretty much open). Only thing I did not check but put my finger in were the risers. I just ordered new gaskets and will pull the risers and inspect them.

Hello again. I did the flowing so far and here are the results
I replaced all the hoses, pulled the oil cooler and power steering cooler inspect and cleaned. These items were all clean. I pulled the risers since this is the only thing in the raw water system. Riser were perfect, and clean. I removed the heat exchanger and this was clean as well. I also pulled sea pump and put in new impeller and wear plate.

So from the transom to the exhaust it is all new and inspected.

My issue now is boat starts fine, idle fine, temp at 160 but when running at 3000 rpm temp starts to climb to 180. I'm sure the boat use to run at 160 before. When I slow down or stop the temp returns to 160 / 170 ish depending how long I wait.

I took it out for the day and it seems to hold at 180.

The only other place that I have not removed and inspected was the outdrive.
The out drive is a bravo 3 and this is where the pick up is. I back flushed the out drive and water comes out fine. I have read that the hose in the out drive could collapse when under suction, is this possible?

Any suggestions comments ?
Should remove the outdrive?

Had the same issue with a boat a few years back. Ran at the perfect temp until engine RPM was above 4k. Turns out debris and a small piece of an impeller blade was blocking the heat exchanger not allowing enough water flow through the engine at higher rpms. Never had an issue after that.

I'm having similar issue. When I get time I'm going to replace the one manifold that's getting hot. Maybe it's clogged in there... Water seems to be flowing good everywhere else

Sorry I should have updated this thread. I found the issue. It was the raw water hose in the drive that leads up to the transom. Apparently, this is a common issue, was not a bad fix but now everything there is new.

Was the hose cracked? If so, it would make sense that once you get up on plane, the hose would start sucking air and compromise the amount of water that it was drawing from the outdrive.

No actually it was corrosion on the hose which collapsed the threaded insert in the gimbel housing area. I removed the hose and installed 2 new inserts (for either side of the hose) and was back in business.