Waterpump plug ?

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It means someone modified yours to block the bypass, so you should be able to use any Windsor thermostat. The Weiand water pumps have this blocked too - actually, Weiand never bothered to drill the pump for the bypass.

Some on this forum will argue that your engine won't run right or heat cycle properly, but all that happens is that the engine begins to work quickly, then the thermostat opens, it cools a bit, it closes, then it warms again, etc... I have the Weiand pump and watch my temp gauge do this several times in the first 10 minutes of driving. No big deal. It works just fine.

Aha.... So that's why my engine always Yo-Yo's up and down between 175-210 degrees ?

Thanks for the great explaining. Now I understand what it does.

Removing the plug & installing the proper thermostat seems like such an easy solution.

shrug?

If the re-circ bypass is plugged, does water circulate at all within the engine and heads prior to the opening of the thermostat? Seems there would be hot spots, maybe even local boiling (heads), and cooler/cold spots (down low in the block) until the t-stat opens and the water pump actually has a place to move the coolant to. Doesn't seem to support an even rise to operating temperature.

quote:

Originally posted by larryw:
If the re-circ bypass is plugged, does water circulate at all within the engine and heads prior to the opening of the thermostat?

the heater hose circuit will flow during warm-up with the T-stat closed if there is no heater control valve installed in the heater core supply hose from the block nipple, or if the valve is open

if the heater core return hose connects back to the water pump, the loop acts as a warm-up bypass. if the return connects elsewhere you'd need to determine if that coolant is recirculating through the engine or being directed to the radiator, but either way there's still ~some~ flow through the heads hopefully enough to prevent the hotspot condition you've described

with no internal engine bypass circuit, and no heater loop, the engine will experience dead head cooling system pressure against a closed T-stat and possibly hot spots in the heads

it's not a big deal to drill the aftermarket water pumps to open the bypass passage if you want to, you could even use a reduced from factory diameter to limit the amount of hot recirculating coolant

I can't imagine that the head gaskets are appreciating the temp fluctuations indicated by the gauge banging from side to side?

The Theory about hot spots and uneven warm up is very interesting.

The way people talk about it, they make it seem like the heads are going to get a hot spot and crack. It sounds like if you run a non-bypass water pump, that only horrific things will happen to the motor.

While the uneven warm up MAY be true, in the real world, there in NO NOTICEABLE warmup or performance difference with running a non-bypass water pump.

I ran one for YEARS without noticing any issue. NONE of the doom and gloom issues happened in my case with a dreaded non-bypass water pump.

However, the Cleveland design works well the way the engineers intended. So there is no reason not to run the Cleveland design. Unless of course, you want to run a non-Cleavland T-Stat or a non-bypass water pump.

My only point is this, a non-bypass water pump works fine. Nothing bad is going to happen if you run one...

I have removed the plug, and have bought the right Thermostat for the 351C with the "hat" - So hope I'm okey for now.

Thank You all for Your inputs.

quote:

Originally posted by ZR1 Pantera:
The Theory about hot spots and uneven warm up is very interesting.

The way people talk about it, they make it seem like the heads are going to get a hot spot and crack. It sounds like if you run a non-bypass water pump, that only horrific things will happen to the motor.

While the uneven warm up MAY be true, in the real world, there in NO NOTICEABLE warmup or performance difference with running a non-bypass water pump.

I ran one for YEARS without noticing any issue. NONE of the doom and gloom issues happened in my case with a dreaded non-bypass water pump.

However, the Cleveland design works well the way the engineers intended. So there is no reason not to run the Cleveland design. Unless of course, you want to run a non-Cleavland T-Stat or a non-bypass water pump.

My only point is this, a non-bypass water pump works fine. Nothing bad is going to happen if you run one...

The uneveness of the warmup and the pulsation from very high to very low in a regular car probably would just be accepted as normal.

In tha Pantera, it makes it uncomfortable to drive the car where you are taking it on faith that it will not overheat.

I ran the non bypass Wieand pump and a regular thermostat for years in a Mustang although if memory serves me right, maybe it was a Cleveland thermostat?

There with a normal distance to the radiator I noticed no issues at all. The car warmed up fast. Held a steady temp.

In the Pantera, the temps pulsated like I was going to have to call the Nuclear Power Commission, sound red alert and give the order to abandon ship.

I didn't need that additional stress.

To each his own.

Engine temps as shown by the water temp gauge 'yo-yo' up and down on mine when the thermostat begins to fail....Installing a new one fixes things for about a year, then the movement returns. Nothing lasts forever.