P11 engine photos

[1941coupe]

I have a 1941 P11 business coupe. I am ready to replace the cracked head and noticed that my car does not have the large cast iron thermostat housing and bypass elbow but a stamped steel housing. I don't know why the P11's did not have the coolant bypass feature like the P12's did, it's an important engineering feature, especially in colder climates and winter use. Is there such thing as a bypass/non bypass water pump? I would appreciate it greatly if anyone can shed some light on this, I would like to know if the current setup on my car is original or not. Also, a photo of another P11 engine out there would also be very welcome Thanks!

=C=

[Niel Hoback]

Is there a casting date anywhere on that head? Does your motor number start with P-11? I don't see a bump on the head but that is a 51 or later thermostat housing. I don't think you can use an older head on a newer block without leaking water. The little cast heater outlet for the top of the water pump is not there either. I think someone has been doing a little parts swapping. Something isn't right here.

[1941coupe]

No date just a number. The P11's did not have the external bypass, on my parts list all of the bypass parts, including clamps, a hose, gasket, bypass elbow, etc are all dashed out for the P11 and not dashed under the P12. My engine casting date is 5-29-40 and the number does start with P11.

The P11 thermostat housing was different than the cast part on the P12 cars. I just don't know what it looks like because I have not seen another photo or drawing of a P11 engine....so I am wondering if mine is original or not as I am ready to change out the cracked head pictured.

The "cast heater outlet" is called a bypass elbow and came with a plug installed on top from the factory. If the heater option was chosen when the car was ordered, that plug would be replaced with an elbow for the heater hose and fitted at the dealership I suppose.

Edited July 7, 2012 by 1941coupe

[greg g]

In my expereince the water pumps for the different systems have either a different backing plate or gasket the allows the holes to align and seal. Then the fitting for the heater connection or the bypass/heater connection is made to match the system.

If anyone can explain the rhyme or reason for whether the car has one system or another please pipe up.

[TodFitch]

In my expereince the water pumps for the different systems have either a different backing plate or gasket the allows the holes to align and seal. Then the fitting for the heater connection or the bypass/heater connection is made to match the system.

If anyone can explain the rhyme or reason for whether the car has one system or another please pipe up.

The water pump part number is the same for P11 and P12 but the bypass elbow is listed as "not used" on the P11. Different thermostat numbers. So I think 41coupe has it right.

I would have thought that the non-bypass type thermostat housing would have been similar to the cast iron one on my '33 but the parts book I have doesn't seem to show an image of a non-bypass housing.

[Niel Hoback]

It's late in the day, but I still managed to learn something today, thanks to this thread.

[old-idaho-iron]

i know i sent these pics to you, but for all the others involved, here's the one i pulled off of my 41 parts car.i'm 99% sure it has/had the original motor in it.

[greg g]

Here is a 35 with external

and a 35 with the internal

and a 51 with internal

a 54 internal

a 57 internal

So again what years and models had external and which definately had internal??

Seems to me that as hoods got lower it got less likely that you would get an external but thats just a guess.

[1941coupe]

Thanks for all the insight and photos. I am starting to believe now that P11's had NO bypass system altogether, which is odd to me that this important feature was not carried through the entire product line. So I ordered a thermostat from Andy B. and this is what I got. I will not really know what I have until the steel housing is off. It looks totally different than the one pictured in the Roberts catalog which looks just like the original shown in the factory manuals.

The photos are reversed....this is what the original P12 thermostats looked like as pictured in the Roberts catalog.

Edited July 7, 2012 by 1941coupe

[1941coupe]

And this is what I received in the mail.

[Jerry Roberts]

The thermostat that you received in the mail is the modern correct replacement for the old style that you pictured .

[1941coupe]

Thanks Jerry. The number on the color thermostat photo I posted reads 180 a 2034. Is the 180 the temperature? It seems like it to me. I realize running these engines hotter is better for them for fighting sludge and efficiency. However, I want to keep it with the 160 because of the heat here in southern California. I don't need any more potential " vapor lock " issues.

Also, per my factory original 1941 parts list book, the P11 and P12 use different thermostats, Jerry, can you tell me why this is?

P11 658658

P12 867040

Edited July 7, 2012 by 1941coupe

[TodFitch]

Thanks Jerry. The number on the color thermostat photo I posted reads 180 a 2034. Is the 180 the temperature? It seems like it to me. I realize running these engines hotter is better for them for fighting sludge and efficiency. However, I want to keep it with the 160 because of the heat here in southern California. I don't need any more potential " vapor lock " issues.

Also, per my factory original 1941 parts list book, the P11 and P12 use different thermostats, Jerry, can you tell me why this is?

P11 658658

P12 867040

P12 has external bypass while P11 does not.

[1941coupe]

P12 has external bypass while P11 does not.

I want to know why the thermostats need to be different specifically/technically. For example, are the different thermostat housings different in size requiring a different size thermostat? Slightly different temp or what?

Edited July 8, 2012 by 1941coupe

[TodFitch]

I know that already! I want to know WHY the thermostats need to be different specifically/technically. For example, are the different thermostat housings different in size requiring a different size thermostat? Slightly different temp or what?

Temperature ratings should set the actuating temperatures for both and the cylinder head outlet and housing bolt pattern are the same for both.

The external bypass type allows flow in two positions: When cold it sends the coolant to the pump via the bypass. When hot it changes to allow flow to the radiator. The external bypass type is taller to handle the two outlets from the housing.

The other type is basically just a on/off valve that sends coolant to the radiator when hot. Since it does not work as a diverter it does not need to cover two outlets and can be shorter.

[1941coupe]

Excellent Tod, Thanks for your input.