Gen 4 cooling
 

Finally got my winter project into the water today :D :D .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?? :mad: 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

Re: Gen 4 cooling
 

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

Re: Gen 4 cooling
 

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

Re: Gen 4 cooling
 

yes

Re: Gen 4 cooling
 

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

Re: Gen 4 cooling
 

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

Re: Gen 4 cooling
 

Is there a Mark V and Mark VI?

Re: Gen 4 cooling
 

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

Re: Gen 4 cooling
 

I have a mk5 and a mk6 in my boat!

Re: Gen 4 cooling
 

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

Re: Gen 4 cooling
 

yes, more then likely it is

Re: Gen 4 cooling
 

I heard of people running a bypass hose from the front to back of manifold,will this help?Or should I drill and tap for the stock bypass from pump to manifold?

Nordic95

Re: Gen 4 cooling
 

You mean to the intake right? Ive never tried to run without one. Your intake doesnt have a bypass port in it?

Re: Gen 4 cooling
 

Yes,to the manifold.Now I'm running Hardin Marine manifold and no provision for the by pass hose.I was told I didn't need it.My Gen 5 doesn't have it either and it runs fine.

Nordic95

Re: Gen 4 cooling
 

can you email me pics of your setup????? just doesnt sound right, this is basicly how it should be set up

Re: Gen 4 cooling
 

Goodt,
Here is a pic of the engines.

Re: Gen 4 cooling
 

I think the problem is the bypass but if you give me a call tomorrow Ill give you some other ideas to try, are you running a dry joint between the manifold and riser???? ( solid gasket, no holes )

Re: Gen 4 cooling
 

Yes,and the manifolds are also brand new Revolution Marines.I also just noticed in my picture that the manifold has a tap for the bypass hose,but that manifold is on the gen 5,the gen 4 is on the right.No provision for the bypass on the manifold for the gen 4.I wonder if the manifolds are mixed up?

Re: Gen 4 cooling
 

Those engines look sweat. Could one of your temp gages be off ?

Re: Gen 4 cooling
 

Thanks,I checked guage and sender.I think its a steam pocket or a hot pocket,just can't eat it!!!

Re: Gen 4 cooling
 

I had the same problems when I put a supercharger on my Merc 425 HP Gen IV engine. The B&M manifold had also no provision.
Therefore I first plug the venting hose located on the top of the circulation pump and the cooling water temperature rose up to 100 degree Celsius (212 F).
After installing a pipe with a restrictor which I drained into the bilge the cooling water temperature became normal.

Joee