Mark 4 Cooling Issues

[ACCar-guy]

Built a Mark 4 with 347 stroker in 2012 with no overheating issues. Employed a 1986 Mustang 5.0 plastic overfill tank. More recently upgraded to stainless steel tube type overflow tank in the same mounting location for appearance purposes. Have experienced new overheating issues including thermostat cycling that sounds like a bad valve lifter and venting of fluid from the overfill. Have replaced the thermostat and burped the system for air entrapment correction, however overheating continues. Thinking of going back to the Ford OEM tank but really unsure of the root cause of overheating? Thanks.

[i.e.427]

Is it actually overheating or just pushing out fluid? The F5R recovery tank is quit a bit smaller in capacity than the stock Ford plastic one.

[ACCar-guy]

Thanks for the great question. Gauge climbs up and engine starts running rough so I have to think it is overhearing.

[Fman]

A few questions for you....

What temperature are you overheating to? Is your fan coming on? Does over heating happen at low speed in traffic? Confirmed T-stat is actually opening and closing? Tested T-stat it in hot water before install to make sure it worked? What coolant mix are using 50/50? What lb cap? What process did you use to burp all the air out of the cooling system?

[i.e.427]

Gauge climbs up .

To what temp? What t-stat temp did you replace it with. With vague symptoms we can only give vague solutions.

[ACCar-guy]

Great questions, thanks. Gauge goes to 110-120 C when overheating (last event in traffic). Cap is 14-18 lbs. Disposed of thermostat box but employed 86 5.0 spec. 50/50 mixture. Burping performed while engine is idling at cold temperature. Most fluid venting occurs after engine is shut off. What is the risk of running NO thermostat in a temperate area? Thanks again for the guidance.

[AC Bill]

If the car had no overheating issues since 2012, and now you've changed the overflow tank, it's bound to be related to that. Did you do any other work, or modifications at that time?

The OEM donor overflow tank, was a vented tank, that allowed coolant to be vacuumed back into the rad, as the car cooled. This ensured adequate coolant levels, and prevented air from entering the cooling system. The golden rule was to never let the overflow tank go dry, don't let the level drop below the cold fill mark.

The smaller fancy looking tank your now using, may not have the capacity to catch all the expanded fluid. If it loses even a little every time your out, eventually you could find it's sucking air back into the system. The other possibility, is the tank is not vented, and that's preventing the coolant being vacuumed back to the rad. If you changed the overflow hose, or routed it differently, is it kinked or collapsing under vacuum?

[NAZ]

Not sure which recovery tank you're using but many out there use two nipples on the bottom of the tank, one goes to the radiator overflow (at the cap neck) and one is a recovery tank overflow. Get them hooked up incorrectly and you will puke coolant that will never be recovered once the system cools down. The overflow nipple is easy to locate as it has a tube that runs near the upper limit of the tank, the one that gets hooked to the radiator draws off the bottom of the tank.

Another thing that will prevent coolant recovery is if the cap check valve is stuck shut and cannot open when the system cools. Or if you use a cap without the check valve. Also, any obstruction in the hose from the radiator overflow to the recovery tank will prevent coolant recovery. Recovery is accomplished by atmospheric pressure which is why the recovery tank needs a vent. So a kinked hose may allow coolant to flow from the radiator (under system pressure) but not the other direction.

The last consideration is the size of the recovery tank, many are really too small for a typical V-8. If insufficient to handle the amount of coolant that is normally pushed out of the system by expansion plus a reserve amount, then some coolant will be lost and not recovered. You can calculate the normal expansion from the operating temp, I calculated mine at 30.1 oz but I always use a 10% fudge factor on top of that and then you want a few ounces of reserve so you never suck air back into the system.

[ACCar-guy]

Extremely helpful, thanks NAZ!