GT-40 overheating

[seveet]

Need help. I have a 1998 ski nautique with a GT 40 engine. After the oil was changed this spring, went out for a set. Got one pass in and the temp spiked. Boat went into limp mode. Wasn’t getting any water flow after we checked the strainer to insure it wasn’t clogged. Got it back to the dock. Checked the water intake and lines no obstruction. Checked the impeller, seemed to be OK but replaced it anyway. Added a garden nose attachment to the line, could get water to flow up to the thermostat. Ran the boat attached to the garden hose. Temps remained OK, but no water in the manifolds and no water coming out the exhaust.  Replaced the thermostat. On the garden hose temps stay low 140 and now a little bit of water coming out the exhaust and in the manifolds but not what I am used to seeing. As soon as I put it in the water and start the boat temps start to spike back the 200. What next?  Thanks 

[MISkier]

Bad water circulation pump?

 

[ReallyGottaSki]

Impeller is probably not at ok as it looks, likely has a good set . Suction comes from the blades springing back to maintain contact.

Edited April 25, 2023 by ReallyGottaSki

[skihacker]

Air leak on intake side of the raw water pump? Cracked seaweed separator or missing o ring? Something like that?

[TomH]

I'd start with making sure you're not sucking air somewhere on the suction side of the raw water pump.  Check/tighten every connection, and clean the o-ring on the strainer and make sure it's sealed up (the tranny cooler ends can sometime get squished/out of round and also be a potential air leak).  The garden hose pressuring that line will hide/mask an air leak there.  Pulling your intake hose off the through-hull and throwing it in a 5 gallon bucket that you run the garden hose into will give you a better idea if it's drawing water as it should.

[MDB1056]

+1 @MISkierraw water pump on the engine (circulation)   

Edited April 25, 2023 by MDB1056

[Drago]

@seveet Make sure you didn't lose or tweak the rubber o-ring top of the clear strainer, also, after the clear strainer is the smaller black metal strainer to the transmission, look up in there.

[MISkier]

I think @TomH also has a good point.  We just went through an overheating scenario with a brand new 200 which was the result of an improperly mounted shutoff valve and hose for the hull water inlet.  The valve handle was making contact with the inside of the engine box and the pressure of that contact was breaking the seal between the valve and the hose, causing a leak and introducing air into the system.  The difference with ours is that the engine would overheat when the boat wasn't moving, but would be relatively fine at speed during a pass.  The reason was the reduction in cooling caused by the leak was overcome by the force of the water pushing into the inlet and there was not enough water just sitting and idling to prevent overheat.  In our case however, the bilge was running after a few passes, as the leak was dumping water into the bilge at speed.  We couldn't see anything leaking when sitting and idling at the dock, though, which baffled us.  Running on the garden hose may supply enough force and, thus, water for you to keep from registering an overheat, but it is still starved of water - as evidenced by less flow through the risers and exhaust.

 

In short, check for a leak in the various hoses and connections of your inlet raw water supply.

[eyepeeler]

+1 on the sea strainer leak.

Surely you already checked for tranny cooler blockage...

Edited April 25, 2023 by eyepeeler

[6balls]

Agree air leak.  When winterizing my GT40 once I didn't have my usual hose segment to suck the antifreeze mix from the 5 gallon pail and there was a pretty good seal but not perfect--ever so small leak.  I figured no problem it would have enough suction to draw thru there---nope.  Grabbed my other hose segment with a better seal and slurped up that 5 gallon pail no problem.  If not air--that's as far as my knowledge goes!  

[S1Pitts]

@seveetIn case the other suggestions do not solve the issue - You said you changed the thermostat. Is it the correct PCM marine type or a automotive type from an auto parts store?

My buddy on his 98 SN changed his thermostat 3 times all with auto type. Overheated by the end of every pass. Put in a new $75 PCM 160 deg and problem solved. 

[6balls]

What is the over/under on how long it will take @Jody_Sealto give us all the right answer?

[Bruce_Butterfield]

My bet is air leaking at the strainer.  Be sure the oring is in tack and try some teflon tape around the threads for extra seal.  Second bet is blockage in the trans cooler.  Third is thermostat.

[seveet]

Thanks for all the feedback. I think it originally was the thermostat, but then I reinstalled the water pump backwards after I changed the impeller 🤦🏼‍♂️. Seem to be back in business.

[morfoot]

Had the same issue with my 99 SN a couple weeks ago. Bought the boat in Dec 21' Put 125hrs on it last year. NO issues. Was boating on the St. Johns River Easter week and temp hit about 205'F. Engine light on. Checked all hose connections and got maybe a qtr turn on each hose clamp. Still ran hot. Changed impeller at the Lunch destination as I figured it was just tired. All blades were there and it was in decent shape but changed it anyway.  Still ran about 190'F. Got it back to GA and ordered a Thermostat from NP. Pulled the housing to change the Stat and it looked a little tired(corroded) probably okay but changed it anyway. Further investigation revealed two pieces of impeller blades stuck in the bypass section of the housing. They were tan in color and obviously a few impeller changes ago before I owned the boat. Go Figure.

 

@seveet... Yep pump 180' out will definitely make it run a weeeeee bit hotter.

[MDB1056]

YIKES……..