mjb

'97 502 cool fuel mpi- Looking at the fuel cooler, the fuel outlet is on the same end of the cooler as the inlet from the pump and the return outlet is on the opposite end of the cooler. Because of that, it seems as though the fuel supply to the rail does not get much cooling and the return fuel to the filter gets most of the cooling??
In conjunction with other changes(cam,heads,ecm,exhaust etc...) I want to plug the return regulator on the cool fuel and relocate a new regulator AFTER the fuel rail and return to filter. ( I was planning on return to tank but I don't have extra bungs in the tank) I'm afraid that the fuel might overheat with this setup since neither supply or new return will get much cooling. Does anyone have any experience with this??
Thanks- MJB

Linster

Don' t get confused, you can not see the plumbing in the cooler. I bet the supply to the manifold has been cooled. The return is probally being recycled.

Not sure on any of these statments, but thats would make sense.

Sean H

no reason to cool the return line, i would say linster is right about the routing inside... the supply probably doubles back in the cooler as the return is a straight shot...

baronbob

I just installed a procharger and had to get into the cooler. The fuel flow comes into the cooler and as a result all departures (rail & return are cooled. The purpose of the regulator is to return the not used fuel. @ idle a lot gets returned and @ WOT most goes up to the fuel rail. ATI makes a replacement block for the return which replaces the stock regulator the outboard regulator attaches to it. My return (after the ATI regulator) dumps back into the separator. You should be able to do all of this as well.

mjb

I do understand how the cooler and regulator works...there does not seem to be any "plumbing" in the cooler. It has an inner shell and an outer shell with the fuel free flowing in the intersticial space between the two shells....just like water flows thru a stainless exhaust elbow/riser. My concern was that because the fuel outlet is only 1" away from the fuel inlet, the fuel would short circuit and not stay in the cooler long enough to get cooled. The return outlet is on the opposite end of the cooler so it does get full cooling.
Its the return fuel that gets hot due to the constant loop effect of going back to the filter and thru the pump over and over. I think mercruiser went too the cool fuel system mainly to cool the return fuel...not the fuel to the rail. That solved the hot fuel/vapor lock problems with the earlier VST models.
My concern was that if I return the fuel to the filter AFTER the rail and block the stock return port on the cooler, I may not be cooling my fuel very well. Would still appreciate some feedback from those in the know. I've got a call in to Bret at Aeromotive to get his thoughts.
Thanks-

Dave_N

This is what I believe to be the deal. You are right, the fuel going to the fuel rail does not get cooled as much as the return back to the f/w seperator. This is how the engineers intended it.

The main purpose of the cool fuel system is not to cool the fuel going into the fuel rail for performance gains, but to try to prevent vapor from forming in the non pressurized components of the fuel system (f/w seperator and fuel lines). Paticularly because these components are engine mounted and can be exposed to a lot of heat. The fuel in the fuel rail is pressurized and vapor can not form there (at least it would take a much higher temp). Thus the need for greater cooling to the return line than the supply line to the fuel rail.

Dave

Raylar

MJB and Dave N are right. All of the various cool fuel systems I have been into including Volvo's , cool the return (unused) fuel since its recycling a lot, round and round and vapor lock and heat soak can cause hard start and sometimes even a fuel lock issues, especially in warm climates and hot engine compartments. You can plug or remove the non adjustable regulator in Merc's system and use a new adjustable regulator to reset fuel pressures anywhere in this side of the circut. On the Volvo's and others, there regulators seem to be all adjustable, so no need to add one.

Ray @ Raylar

mjb

Thanks Dave- thats what I thought. Looks like I will need another fuel cooler if I move the regulator to the rail.

DonCig

I have a question along the same lines as this thread.

The High Pressure Merc. electric fuel pump, as part of the Cool Fuel System, on my engine (1997 350 Mag MPI) is a Merc. high pressure pump (30 psi) and matching Merc. regulator for use on the stock fuel injection system that came on this engine.

I am going to a carburated set up on this newly rebuilt engine, can I just place a high quality fuel pressure regulator in the fuel line right before the carburator and contine to use the Merc. Cool Fuel system?

In going thru the merc. parts catalog, it appears that I might be able to replace the electric pump and regulator with a low pressure unit. Is there any reason to do this?

Thanks,


Don

Raylar

Don:
I beleive if it were me I would just strip of the Merc system and replace it with a reasonably priced aftermarket low pressure (carburated) fuel pump and regulator assembly. Fuel to a carburator does not recycle and generaly does not need to be cooled unless you are operating in an extremely warm climate with the boat where warm fuel vapor lock could be a problem. You could use the existing system with another fuel pressure regulator to set the fuel pressure for a carburated motor, but the recycling of the fuel (constantly) would probably just raise the risk of heating the fuel over non-recyled fuel.

Ray @ Raylar