4.3 OMC Cobra Overheating at times

[Ski Bob]

I have a 1991 Four Winns 200 Horizon 21 foot ski boat. I have owned it since new. It is in MINT condition, almost NO ISSUES in 30 years, especially engine related. Has a Chevrolet 4.3 Cobra. Now, recently, and this weekend I was able to do more testing in the lake, I am getting an overheating issue. I have always thought it was due to weeds in lake etc. BUT, daughter has SAME engine in 1 1997 Bayliner, plows through these weeds like they are not there. I simply cross them and up temp goes to overheat. Even with reverse, bla bla bla to clear weeds stuff, often is not a solution. So, here is this weekend tests. Pull tubes and water ski people, heavy pulls, several hundred pounds in large tub etc, stays solid at 175 degrees. But, if they fall, I pull up, put in neutral, MIDDLE OF LAKE, NO WEEDS, it climbs slowly to alarm temp at 220 and if reverse or going does not start cooling, I have to shut down before destroying engine. If I wait like ten minutes, listen to the darn thing bubble hot I restart and immediately or within 15 seconds it begins to return to 175 degrees. I was able to repeat this issue four times. Now, if when I stop, if I put in neutral and push gear bypass and run it up to say 2500 to 2800 RPM, It does not heat up at all. I have never replaced anything related to cooling system in 30 years. A few years ago in previous post with thumping sound I did open up top of stern drive to see impeller (plastic) looked new. Help please. Thanks Bob

 

[dubs283]

I have never replaced anything related to cooling system in 30 years.

replace the impeller

should be done at least every few seasons if not more often

 

[Lou C]

You’re not cooling at low revs. The impellers do wear you can’t really see it unless you pull it out. If you pull up silt or sand it will score the wear plate which also reduces pumping volume. I have had nearly the same boat almost 20 years and I usually change the impellers every 3/4 seasons. The other thing that can cause problems or at least it did for me was the plastic water screen in the lower unit. My boat is moored in salt water and anti fouling paint is a must and more or less constant issue. I had barnacles and other growth on that screen no matter how well I tried to get the anti fouling paint on it. So one year I decided to split the lower & upper gear housings and removed that screen and left it out. Since then no problems with elevated temps. The fact that the engine heats up at low revs but cools off at high revs points to your raw water supply. I’d also remove the thermostat housing and clean out all the ports. Lastly your exhaust manifolds and elbows could be clogging with rust after all that time.

 

[Ski Bob]

Ok, I want to thank you two from the bottom of my heart. So, I pulled the housing open, piece of cake! Attached is a photo of exactly the position of the impeller blades and notice one is actually pointed the other way!! Ugh. So, I did find two impellers (OEM) and bought both as OMC is gone! Sadly, they did not have the gasket. Do I simply clean it nice and put back together? As the back metal plate DID NOT come off. By the way, the intakes are LIKE NEW as boat is NEVER moored in water. Always trailered and dried off every trip. Anal kind of guy as I can't afford a new one?

 

[Lou C]

Ok the blades do flip like that not to worry. What does the wear plate look like? If it’s smooth and not grooved you might get away with not replacing it but that’s not the right way to repair really. If you don’t have a new gasket for the housing then what you can try is to cost the old one with a thick marine grease like Evinrude triple guard grease. The “right” way to fix these is to replace the impeller, wear plate, that metal cage and inspect the housing for distortion. If it’s good you can reuse the plastic housing. That housing has a bleed hole with a little nipple on the outside that connects to a small hose. That hole must be open as it allows the impeller to prime by letting air out of the housing and water in as the outdrive is submerged in the water.
My advice is to buy an OE kit...there is one that has all the parts except the housing and one that adds the housing which is about $40, basic kit is $40. You can get the OE kits easily on line from marineemgine.com or Crowley marine.com. Contrary to what people think common OMC Cobra replacement parts are readily available, you just have to order on line. You can buy in person if there is an Evinrude dealer still in business near you.
Aftermarket is not as good but if that’s the only option use a Sierra kit. Do not mix n match parts, if you put a Sierra impeller in an OMC housing it may not pump right. So if all you can get is a Sierra impeller use the whole kit including the housing
When installing the metal cage it should be glued in with OMC gasket sealer (Permatex Aviation also works). Lube the impeller with water & Dawn dish soap. When starting it on the water hose the first time this will get water up to the impeller faster:
Hook up muffs turn on water
Go up to the engine and disconnect the hose from the transom mount to the thermostat housing at the housing. Hold this hose up and fill it with water with Dawn dish soap. Then reconnect it. This will put soapy water right in the impeller housing so your new impeller gets lubed at start up. I do this any time that boat has sat a while on dry land.
Hope that helps...
PS here's one I took off a few weeks ago, used about 4 years, looked good at first but then you can see wear marks and stress cracks starting to form when you look closely.

PS the boat looks great, I have the same boat but a 1988. Mine's been in salt water over 20 years so I'm sure its needed many more repairs. I had to replace the deck from in front of the helm seats back to the engine in 2006/07. It lives on a salt water mooring during the season here in Long Island.

 

[hugh g]

Ok, I want to thank you two from the bottom of my heart. So, I pulled the housing open, piece of cake! Attached is a photo of exactly the position of the impeller blades and notice one is actually pointed the other way!! Ugh. So, I did find two impellers (OEM) and bought both as OMC is gone! Sadly, they did not have the gasket. Do I simply clean it nice and put back together? As the back metal plate DID NOT come off. By the way, the intakes are LIKE NEW as boat is NEVER moored in water. Always trailered and dried off every trip. Anal kind of guy as I can't afford a new one?

That's a nice looking boat, you don't need a new one. I always admired the look of Four Winns. Just keep up on the maintenance on that drive, especially the shift cable. Those Cobra's are bulletproof if you take care of them. Mine was 34 years old when I sold it & it still ran like a top.