gt 40 cooling issue

If I was fighting a frustrating issue for a long time and I could fix it for under ten bucks before a summer holiday weekend, I'd be very happy man, even if said part could be had a little cheaper elsewhere.

So, did the original poster get his gasket and go skiing or what?

Thanks for the part number, my GT 40 has the gasket that looks like it came off an oil filter. Both my Nautiques have run a water filter/strainer. They do catch leaves and things all the time. My Malibu had no strainer on the intake water line. I guess all the leaves just end up in the block or go out the exhaust?

Hollywood, would you happen to have a part number for the McMaster source on the seals? Maybe what years it would cover? Thanks

I made a silicone gasket for my 78 Nautique, it worked for years. I filled the Oring slot with silicone, coated my cover with light grease where it would be touching the silicone. Installed the cover and let it dry. The cover still came off normally because the grease kept it from sticking closed. I used that gasket for years.
I think your lack of gasket created your issue. A minor air leak will give all of the symptoms you mentioned. Congratulations on a cheap fix although you had several headaches first.

Nice!

Keep us posted.

John,

There's three different overheating at idle boats going concurrently in this thread, so it's easy to lose track.

The set screw indicates which way the pump is facing. Per Hollywood, in is correct for a Left Hand Standard (Most GT-40s are) engine. Also, you'd be overheating at every rpm if it was faced wrong.

1.) Yours if fine anywhere but idle, right?

2.) Was there anything changed etc. before the overheat?

3.) If yours is getting hot at idle, 190ish, are the exhaust manifolds too hot to put your hands on, or is this just a gauge indicated overheat?

4.) You replaced the impeller:
     A.) Did you correctly position the thin o-ring
     B.) Did the kit come with a paper gasket and if so did you put it in (shouldn't reallymatter, but just wondering
     C.) Did you use a PCM or Sherwood impeller or an off-brand?

5.) Do you have a quick flush kit installed anywhere

6.) Did you check your strainer for blockage and presence of gasket?

7.) Did you check your tranny cooler for blockage, end crushage? Hose clamp snuggness?

8.) Any other gauges giving wonky indications?

Yes it did, that was why i changed it last year. I was hoping it solved the issue.

If none of the above solves your heating issue the engine water pump may be suspect. I have seen the impeller on some pumps rust away till it is ineffective and I have seen the impeller lose its clamp on the shaft and free spin rather than pump water. Rare and the last thing I would check but possible.

Given the order of events maybe the manifold, or some hose or fitting associated with it, is in fact relevant.

I would remove the hose going to your new manifold, but not on the manifold side, on the t-stat side. Now, try to blow through the hose, so your blowing through the coolant passage in the manifold. I have to admit, I've never done this, so I don't know how much resistance to expect. But, I'd think you'd know if there's excessive back pressure.

All of the water eventually needs to escape through the exhaust manfifolds, so if it can't escape for some reason, everything is going to overheat.

Your leak may be the intake hose itself. A crack or tear, any leak path that will allow air to suck in rather than water.
Can you try the bucket test with a new hose? Sometimes these hoses are as old as the boat and they crack.
The only way I can think of to test the hose would be to pressurize it.
Plug one end and clamp a garden hose in the other end and turn on the water. If properly sealed you should see no leaks from garden hose pressure.

The pump is correct for your engine. The hoses should be tucked close to the block for Left hand rotation. It would overheat immediately if it was on backwards.

Yes it use to cool fine, the previous owner did replace the pump before I purchased it about 4 years ago. There is a Sherwood tag on the the pump. I put in a PCM Impeller and new gasket when I replaced it. I don't see any water leaks around the pump. The whole seems odd to me, I thought if the pump was in wrong there would be no water and overheat at all RPMs.

Okay I did the bucket test it takes about a min to pump a 5 gallon bucket full of water. I also connected longer hose to the raw water pump intake to take water directly from the bucket to bypass the strainer and potential clogs. The result was the same draws very little water still warms up to 190 at idle.

Can someone tell me if the pump is installed correctly. I have never switched the direction but it doesn't look correct after all the images I've seen.

I am having the same issue. I have a 96 Sport Nautique, replaced the impeller last year, no water leaks that I can see and when I'm running at 10mph the engine cools right down. At an idle(once the engine is warmed up) it starts heading to 190 quickly. Goes back down as soon as I hit the throttle. I checked the strainer, it was clean. I pulled a hose on top while it was running and it was pumping, although I thought it should be a little more than it was.

No quick connect installed for flushing. I guess I need to complete the bucket test.