Help! ‘06 RXP Coolant loss, overheating at high rpm but pressure test is fine dockside…

[Mike071481]

Just bought this 2006 RXP with 132hrs as a first PWC (from my dad) and it turns out it had a few issues… first, the rpm would only reach 7200 and it maxed out at 45mph (turned out to be disconnected hose from supercharger).

Now that it gets up to 8300rpm or so it overheats in about 1 minute due to lack of coolant.

Not sure where leak is (bilge seems ok) so bought a pressure tester and pumped to 15psi which it held fine! Oil is clean and compression at 130 across all 3 cylinders. Thought maybe it was overheating because I kept filling with lake water but I just added a gallon of coolant and that’s all disappeared after one run…

I’m new to seadoos but no stranger to mechanical stuff and I’m at a loss here! Any suggestions before I throw in the towel and take it to a mechanic? Thanks in advance for any advice!

 

[Digdog]

You cannot have a good pressure test and be losing coolant , it has to either be in the crankcase , bilge , or leaking out the ride plate. You could have a bad head gasket but that would result in the coolant in the bilge, leaking seal in the water pump would be in the bilge , stuck thermostat would boil out of the tank into the bilge , hose connection leak would also be in the bilge , bad cap would also be in the bilge. Do not run straight water , the pump seal is ceramic and it will fail , use a low silicate coolant like the factory or OEM Orange 1

 

[Mike071481]

Thanks for your well thought reply! It looks like there is some coolant in the bilge, more than there should be from spilling… I’ll re-test the pressure and see if I can find the source, maybe I didn’t hold it for long enough. Just seemed to empty the tank so quickly I was surprised to see the needle hold at all! Hopefully it’s not a head gasket, not wanting a big project at the moment…

 

[BGS]

So if you have air in the system, There is a procedure for re-filling cooling system, 2005:

Refilling the System
Watercraft should be level, engine cold and drain
plug removed for refilling.
Place a container under drain plug to collect antifreeze.
Ask someone to pour antifreeze in expansion tank
while watching antifreeze and air bubble flowing
out through drain hole. When no air bubbles
escape, reinstall drain plug. Torque to 8.3 N•m
(73 lbf•in).

Continue to pour and fill expansion tank between
marks.

1. Level between marks when engine is cold
Do not install pressure cap at this time.
Properly cool exhaust system by installing a garden
hose. Refer to STORAGE section.
Start engine and let run for 2 minutes. Stop engine
and wait 15minutes to cool down. Refill tank
as necessary.
Repeat this run-stop cycle 2 - 3 times until thermostat
opens and stop engine.

 

[KG1974]

Just like Digdog said, that actually happened to my ski, the one in the picture......where I rode on the river for a short time, then all of a sudden it went into overheat alarm. Shut the ski off, opened the back seat, and saw all the coolant steaming and coating the entire back half of the inside hull, the bottom of the hull, and all rear engine parts. I let it sit for a while to cool, but limped it off the river, got it back home, and in theory suspected either a stuck thermostat, or a blown head gasket. I figured the head gasket was fine because I let it sit on the river for half an hour to cool, enough to crank it back up......well it did crank back up and actually had some pull........so I suspected the thermostat. I since pulled the head and replaced the head gasket anyway, with a new OEM gasket. Also replaced the coolant pump assembly with a complete new unit, but I ordered the 160 degree pump from Greenhulk. The thing cost $375 but I have since ran the ski at 8800 rpm @ WOT on a custom Maptune several times and everything is fine.....no leaks, no blowouts, and the temps seem to be within operating range. I also have since replaced the coolant temp sensor and the EGT sensor. The coolant doesn't dip at all in the coolant bottle. The stuck thermostat is why all my coolant blew out, and it blew out thru the coolant bottle vent hose.

 

[Mike071481]

Thanks @KG1974 I’m starting to suspect a stuck thermostat as well… pressure test goes down a bit eventually, when left overnight it drops to about 5psi (from 25psi) but the coolant stays put, nothing since I emptied about 10L from the bilge.

That would explain overheating of the engine and maybe causing the pressure cap to release into the bilge…

It sure only really happens after a few minutes at full throttle. Anything less it seems to lose coolant much slower and not overheat…

Next step will be to remove thermostat (or drill out) and try again

 

[KG1974]

Yep that is exactly what mine was doing........I would fill the coolant back up but by morning it would all leak out again. I would be willing to bet your dealing with a stuck thermostat.......your ski has all the classic signs, especially from the results of the leak test, and what the coolant is doing now. The thermostat is blocking the coolant to the ride plate, so the coolant that is stuck in the cylinder jacket and up to the thermostat is boiling out. If you can afford it, man I would seriously consider just biting the bullet and ordering the 50 degree thermostat pump from Greenhulk store......I can tell you I been running the crap out of my ski like i stole it, and I know I am pushing the limits of the coolant temps, but it handles it very well........very worthy investment, and gives peace of mind that you won't break down miles from the dock.

 

[Mike071481]

Ok, new update… I removed and checked the thermostat- seemed to be working ok - decided to try gutting and reinstalling to prove it wasn’t causing blockage. Re-assembled and tested, overheated again within one minute. Added temp sensors to engine coolant outlet and return from ride plate and rode it without seat to see what’s happening. Within a minute the engine coolant is 130 degrees Celsius (from ride plate is 80 degrees C) and pressure is over 20psi, coolant spraying out of reservoir… Suspect now that it’s head gasket. Will try removing plugs and re-pressurizing coolant system overnight next time I’m down at the boat.

 

[200mph]

Could try something similar to this to verify head gasket issue.

Combustion Leak Detector