nordic95

Finally got my winter project into the water today .Boat ran great,but I still have a couple little tuning issues to deal with.Here is my question:

Boat has a gen 4 and a gen 5 502 engine,Don't ask!!The gen 5 ran good all day and temp stayed at 135 till ran hard and went up to 150.Two to three pounds water pressure in both engines at idle and around 27 psi a 5000 rpms.The gen 4 ran great but water temp went up 180 and then down to 130 again and again.I changed thermostat and it didn't make a difference.What the heck would cause this?? Motors are brand new and I know first hand there are no restrictions in cooling system.Could it be a steam pocket??Both motors have stock circulating water pumps.

Please help,I know someone here has had to have had this problem before.

Nordic95

GOODT

The gen 4 is cycling, it could be the way it is plumbed or you might just have to put a by pass hole in the stat

RLW

What's a Gen 4? Is it the same as a Mark IV?

nordic95

yes

nordic95

The plumbing is all stock basically,except I just ran the hoses a little differently but to the same locations.I read a lot of post on here last night and it seems steam pockets are a big issue with the Gen 4.I am going to try and drill the thermostat today and see what happens.I think it is because right next to the thermostat housinf the manifold gets real hot,can hardly put a hand on it,then it cools quickly.The rest of the motor stays nice and cool at all times.

Thanks Goodt

GOODT

from what you discribe I think drilling the stat should fix your problem

RLW

Is there a Mark V and Mark VI?

nordic95

I drilled the stat today and it didn't make a difference.I started out with two 1/8 holes and then drilled two 1/4 holes,temp still rises and then falls back to 130 degrees.Now what should I try,any solutions????


Thanks Nordic95

jryan26

I have a mk5 and a mk6 in my boat!

nordic95

Hey guys,


I just noticed looking at pictures of my old motors that I did remove the 1/2 bypass hose that goes from the top of the water pump to the old thermostat housing.My new housing does not have a provision for it.Can this be my problem?I think this would put water pressure from under the thermostat,is that right?That would act like a large hole in the thermostat to keep pressure even on both sides of it,I think.

Nordic95