1990 Sport Nautique - running hot at idle

[WCS]

Quick rundown. Took the boat out after winter and changed all fluids tranny & engine. Fake-a-lake in the driveway and the boat ran for 5 or so minutes at 145 degrees (no problems). Put the boat in the water (100 outside with water temp about 80) and the boat ran up to 200 degrees within 10-15 minutes of idleing out. Ran the boat up to speed to see if it would cool down and temp dropped to 160, idled boat back down and it heats right back up. Loaded the boat up, changed the impellor, stat, checked all hoses/hose clamps and water strainer. Fake-a-lake in the driveway and could not get the temp above 145. Put the boat back in the water and it does the exact same thing. Any ideas????

[WakeSlayer]

You have an air leak. Check your strainer to make sure the gasket is in it, not cracked, and snug. Then take a nut driver (not a screwdriver) and tighten every hoseclamp on your motor's colling system. Your problem will be solved.

[WCS]

I tightened all of the claims and checked the strainer. I'm thinking maybe I have a bad hose somewhere. I could not find any leaks and the boat stays very dry. I am getting some flakes (rust/mtl) out of the manifolds (left & right) when I drain them after use. Could a clog in the manifold cause this?

[pdr3842]

Check the strainer.

It could have a crack that you missed. Look to see if water is flowing through it when you are running the engine.

[WCS]

I am going to go through the entire system again this weekend and will post findings. Thanks.

[91xl]

mine is doing the same thing i suspect it is the manifolds not flowing enough water out, the previous owner of my boat said the manifolds will need to be replaced soon that was a year ago. mine also will climb to about 180 when running at 30 plus mph and drops when i slow down. my risers are hot to the touch showing they are partially plugged.

[WCS]

Mine cools down quickly once you get up to speed, as soon as I idle down to pick up a rider the temp starts to rise again (190-200 way to hot). You would think it would at least get warmer than 145 during the fake-a-lake. Put the boat in the lake and and the porblem starts. Had zero issues until I took the boat out of storage.

[91xl]

same with mine last year was fine this year it started. mine doesnt get hot on the hose either but the hose is forcing water to the raw water pump probable harder then just sitting in the lake. and it is not seeing the same loads of pulling a skier which makes more heat

[jmo]

A few thoughts - The heat transfer rate will be directly proportional to the temp differential between the cooling water and the engine so when you run via fake-a-lake the water is coming from underground and is probably at 40 degrees and hence is enough to keep the engine temp in check.

The rate of heat transfer will also be proportional to the flow rate of the water through the cooling system as this helps maintain the largest temp differential. The flow rate in our boats is directly tied to engine rpm's, so at 3000rpm your flowrate is 3x of what it is at idle or no wake speeds.

Not sure how much more heat the engine puts out at high rpm versus low rpm, but it's clearly less of increase than the impact the increased rpm's have on the ability to cool it.

[91xl]

flow rate assumes all is in good working order since the water exits the risers, which are restricting flow in my case anyway, plus in south west georgia were its currently 100 outside, water out the hose is pretty warm almost bath water.

[EchoLodge]

If your risers show signs of leaking on the outside then they will be leaking on the inside. I just replaced my risers and exhaust manifolds on my 90 SN before I sold it to my buddy. My water jackets were not clogged but def were not as open as new. If u do decide to check and take risers off you may find the bolt rusted and the head can snap off like mine did. On a positive note. All the bolts came out of the manifolds.

*Tapatalk Via Android*

[91xl]

echolodge if i only get so lucky my boat was a salty. i think all but maybe one will break. the risers are not leaking but are plugged they get pretty hot when running hoping to milk till winter and going to replace along with heads and intake. which will take care of my running warm issue i believe

[azeus17]

mine is doing the same thing i suspect it is the manifolds not flowing enough water out, the previous owner of my boat said the manifolds will need to be replaced soon that was a year ago. mine also will climb to about 180 when running at 30 plus mph and drops when i slow down. my risers are hot to the touch showing they are partially plugged.

What makes you think they are plugged? Being hot is not a real good indication of this becasue if your temp is at 180, yeah, they are going to be hot to the touch. You sound like you have the oposite problem as the original poster. Your situation sounds more like you are not pushing enough water through the engine because it is heating up at speed and cooling at idle. Do a bucket test. Put the intake side of your raw water pump in a full 5 gallon bucket and start the engine. It should suck it dry in seconds. If it take much longer than about 20 seconds, I would check your impeller and hoses for pieces of old impeller. I replaced the maifolds on my 89 sport, when I owned it, and was surprised at how good the risers actually were after 21 years, most of which in brackish water. Not saying they could not be plugged, but I would check some other stuff first.

Wakeslayer was dead on about the original post. Sounds like an air leak because he heats up at idle and cools at speed when the pump is pulling more water. An air leak will be on the vacuum side of the RWP...somewhere between the pump, strainer, trans cooler and the through hull. Checking for water leaking is not really going to tell you much becasue the air is leaking into the system, not water leaking out. If you have not done recently, replace all the cooling system with new hoses AND clamps and be careful not to over tighten the clamps as they can be stripped. Pretty cheap and it gives you peace of mind. (New hoses don't look bad either

[91xl]

mine runs warm at idle also and above 30 mph in between it runs at 160 all day long. did check raw water pump first its in good shape plus i have a spare pump. i know the previous owner of my boat and its from the tampa bay area so its salt not brackish, every one i know there replace manifolds and risers quite frequently. my buddy has an excel and has replaced the manifolds a couple of times because of the salt and actually the last ones got so plugged that it burned a hole in the muffler. i think i will check for a vacuum leak also though.

[WCS]

Just an update guy's, problem solved (broken clamp on the hose where the water enters from the bottom of the boat). No more overheating issues. Thanks for all the input.