tonejunkie99

Hello there'
I have a 1999 fountain with a 502 EFI that the temp fluctuates between normal up and down to as high as 200+ under power, but sits at the thermostat rating when at idle. The things I have already done are change RAW water pump, change circulation water pump, changed the pick/up line and flange going through the transom down the lower unit to inlet, I have changed the thermostat, back flushed the system, changed the exhaust manifolds and risers. I have also removed and inspected all peripheral hoses and oil/fuel/hydraulic coolers.

The current thermostat is a 160 and the boat idles around 160 degrees but when I shower down on the throttle the water temp starts rising upwards of 200 as the rpm's approach 3500 sometimes it will come down on it's own other times I have to play with the throttle.
My last test was to remove the thermostat and see if the engine still overheats, the result's of that test is the engine temp barely rose over 100 degrees. I am wondering if I am using the wrong style thermostat because these things don't seem to open when they need to... Is the hot water hitting the wrong side of the thermostat or could I have it upside down? I don't think it can go in upside down... it's currently installed where the springy side faces you when installed in the thermostat housing and then the plastic retainer goes after with the openings facing the water passages according to all the pictures I'm seeing it seems properly installed.

I'm inclined to think that hot engine water is not heating the coils on the thermostat and I am considering drilling some 3/16 holes in it to allow for some pre circulation? Or do I have the wrong thermostats all together? the boat has had this issue ever since I've owned it and I just matched up the thermostats with stainless steel thermostats from Orilleys auto parts. could it be something as simple as this?

thanks in advance for any advice

Kindest Regards
DW

Griff

The spring side goes down like this https://www.amazon.com/Mercury-Quick.../dp/B001HBSY4A
http://www.mercruiserparts.com/bam/s...31902/1614/200

and you have to use a Merc or QS gasket with the metal crush points and no sealant or your temp sender will not work.

SB

This is the pic you are referencing, right ? And this is your style t-stat housing ?

AllDodge

Sounds like maybe Bravoitis to me, where the drive hose comes out of the transom assembly and connects to the fitting.

[ATTACH=CONFIG]566709[/ATTACH]

There was another which found a small shell inside the hose which was reducing the water flow

tonejunkie99

Yes that is my housing and the drawing I used for reference, that is what my thermostat looks like also...

tonejunkie99

I used such a thin amount of silicone, I cant see this being an issue, plus the retainer keeps silicone from getting inside the housing area.

tonejunkie99

I've changed all that the hose and flange, if there was a restriction on the raw water intake, the engine would still overheat, even without the thermostat. No thermostat the engine temp is slightly above 100 degrees

1BIGJIM

Nobody mentioned the hose that goes from bell housing/helmet to transom. I had one twist one time that caused the same problem you describe.

tonejunkie99

has anyone ever drilled holes in a thermostat to help maintain thermal circulation?
it seems like the only way left to go for me since the engine is either too cold without a thermostat or fluctuates between extreme highs when installed.
I have literally tested, cleaned, flushed and changed everything in the cooling system. I'm run out of options. I've changed every culprit in the system, followed every advice from reputable many performance marine shops.
Kindest Regards
DW

tonejunkie99

already done >>>> changed the pick/up line and flange going through the transom down the lower unit to inlet, <<<
the engine runs cold without a thermostat, if there was a restriction on the primary (intake raw water side) the engine would run hot even without the thermostat installed.