Suzuki DF90 overheats at idle - HELP!

Draig

Cadet
Joined
Oct 7, 2009
Messages
6
Hi Fellas

The root cause of this one is proving a tricky one to track down. Would appreciate any help / Advice I can get on this.
Suzuki DF90 (2003) low hours (<200) 90% fresh water use.
Never had a problem with this motor before - it's been great.
Been stored in garage all winter - unused for 5 months. (now summer down here New Zealand in January).
Changed oil and plugs. Took it to the local tech to get the impellor changed (suzuki part). First time used the boat it goes great (just the same) but after it's warmed up and you put it in neutral and let it idle for a few minutes it sets off the overheat alarm. Restart and cruise and it's good again. Back to idle and > overheat!!! This has continued for the last 4 uses.
So check:
Peeing ok - seems to be a good steady stream even at idle although a little reduced in force at idle.
Thermostat opening - opens at about 60C but just a little bit.
Visually checked the temperature sensors on the head and exhaust manifold and they seem intact - I will measure the resistance on them next to ensure that is within spec.
I have a workshop manual but it does not really help in diagnosing the root cause on this problem.
A ECU dump would help as it would tell me the temp of each sensor when the alarm is triggered but the tech does not have one and the nearest is a 5 hour drive away!
How best check that I don't have restricted water flow through the system - I assume the pilot jet peeing just tells me the water pump is pumping - looking at the cooling water route chart I figure you could still have a restriction upstream and the pilot would not be affected.
Starting to tear what little hair I have out over this one - Local tech not making much progress either - Any pointers fellas?

Thanks in a advance for your help.

Draig
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,880
Re: Suzuki DF90 overheats at idle - HELP!

Does this motor have a pressure relief valve in it?
If it does you need to check to see if it is stuck open, dumping too much water at idle.
Thermostat on my Yamaha is suppose to start opening around 50C and full open at 60C (3 mm)
Do you have a manual to get specs for yours?
 

JRJ

Commander
Joined
Sep 11, 2001
Messages
2,992
Re: Suzuki DF90 overheats at idle - HELP!

Water Pressure Valve: Clean or replace if necessary.
Thermostat: Clean or replace.
Water Tube: Check.
Water Pump: Check.
Hopefully its not a blockage in the cylinder head or block. Good luck.
 

Draig

Cadet
Joined
Oct 7, 2009
Messages
6
Re: Suzuki DF90 overheats at idle - HELP!

Does this motor have a pressure relief valve in it?
If it does you need to check to see if it is stuck open, dumping too much water at idle.
Thermostat on my Yamaha is suppose to start opening around 50C and full open at 60C (3 mm)
Do you have a manual to get specs for yours?

Hi

Yes it does have a pressure release valve - will check to see if it's not sticking. On idle with the cuffs on it does seem to discharge a lot of water from the lower cowling - not sure if that is normal.

Thermostat spec says 58-62C. Test method - insert a piece of thread into seat and heat water to spec. Should release thread at spec. Mine seems to conform to this.

Thanks
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,880
Re: Suzuki DF90 overheats at idle - HELP!

Not very technical to say use a thread. Must not be a factory manual. But you should be able to see how far it opens and if it does not over heat at high RPMs then I would guess it opens far enough. Sounds like the PRV sticking open but that is just an opinion from a fellow boat owner.

If the only thing that was replaced was the impeller that might be a problem too. I like to replace the cup and plate also ,because of the wear sometimes does not allow for a good seal.
Also never start motor with out water covering the pump as it will tear the rubber impeller in just a second or two if conditions are right.
 

Draig

Cadet
Joined
Oct 7, 2009
Messages
6
Re: Suzuki DF90 overheats at idle - HELP!

Not very technical to say use a thread. Must not be a factory manual. But you should be able to see how far it opens and if it does not over heat at high RPMs then I would guess it opens far enough. Sounds like the PRV sticking open but that is just an opinion from a fellow boat owner.

If the only thing that was replaced was the impeller that might be a problem too. I like to replace the cup and plate also ,because of the wear sometimes does not allow for a good seal.
Also never start motor with out water covering the pump as it will tear the rubber impeller in just a second or two if conditions are right.

Hi

The 'Thread' bit - my sentiments exactly - I would have expected a unit of measurement but I assure you that this is from the Suzuki FACTORY manual.

Will check out the PRV and report back.

Thanks
 

Draig

Cadet
Joined
Oct 7, 2009
Messages
6
Re: Suzuki DF90 overheats at idle - HELP!

Water Pressure Valve: Clean or replace if necessary.
Thermostat: Clean or replace.
Water Tube: Check.
Water Pump: Check.
Hopefully its not a blockage in the cylinder head or block. Good luck.

Thermostat - done
Water tube - Going by the manual I beleive I would have to dissasemble the mid unit to get at this. Could I drop the lower unit, connect a hose to the bushing, disconnect thermostat housing and look for good flow without the motor running? Would this discount the blockage theory? I will of course check out the PRV before doing this.
Water pump - motor is 'Peeing' good with the new impellor so I assume that this is OK.

Thanks
 

JRJ

Commander
Joined
Sep 11, 2001
Messages
2,992
Re: Suzuki DF90 overheats at idle - HELP!

Thermostat - done
Water tube - Going by the manual I beleive I would have to dissasemble the mid unit to get at this. Could I drop the lower unit, connect a hose to the bushing, disconnect thermostat housing and look for good flow without the motor running? Would this discount the blockage theory? I will of course check out the PRV before doing this.
Water pump - motor is 'Peeing' good with the new impellor so I assume that this is OK.

Thanks

As long as you have the factory, I can't add anything. I never had to chase a water tube. Good luck.
 

stylesabu

Master Chief Petty Officer
Joined
Aug 2, 2009
Messages
849
Re: Suzuki DF90 overheats at idle - HELP!

does the temp of the water coming out the pee hole feel the same temp. verifiy that it is actually much hotter. a digital thermoeter is help foir this. I'm just saying make sure that it is actually overheating. then whats opening at part-full throttle, that not at idle? sounds like a pressure relief valve.
 

Draig

Cadet
Joined
Oct 7, 2009
Messages
6
Re: Suzuki DF90 overheats at idle - HELP!

Update guys

Tech checked out PRV and found small gravel/grit in there.
Cleaned it all out and it now runs fine at idle on the cuffs. Will try it on the water sometime soon but hopefully that was the root cause.
Many thanks for your help everyone!

D
 
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