Coolant by pass. Why?

davem201m38 · Post by **davem201m38** » Sat May 30, 2009 3:27 am

I'm just fixing some moinor problems to get me through the next week until I can perform an engine swap whena question came to mind.

Why does my M38 engine have a coolant by-pass from the head to to water pump when my MB engine doesn't.

Among my 'spares' I have various heads with by-pass openings and heads with cast blanks for a by-pass opening that have not been machined and I have similar pumps with no eveidence of a bypass, a blank unmachined by-pass and machined by-pass opening with treaded plugs.

I can't honestly say that the by-pass facility seems to make any difference to the warm up time or running.
So apart from alowing some place to tap off warm water what is the point?
Thanks,
Dave.

Post by **wesk** » Sun May 31, 2009 9:01 am

The only point for the bypass is to accelerate an even warmup. Without it the termostat just doesn't let the coolant move. Without circulation the coolant in the hottest area of the engine (cylinder barrel water jackets) would not move and simply start to boil before the thermostat begins to open. This can cause premature wear and the uneven heating causing some warping over the long term. Also when a heater is installed it's core coolant suffers the same no movement problem that the rest of the coolant system suffers and this means the heater will not emit heat untill after the thermostat opens.

davem201m38 · Post by **davem201m38** » Mon Jun 01, 2009 8:18 am

Oh I see. Thanks Wes, so would it be a good idea to modify my MB to have a by-pass?

I have cast in blanks in the water pump and head and it wouldn't be much trouble to get these drilled and tapped.
Thanks,
Dave.

Post by **wesk** » Mon Jun 01, 2009 8:48 am

Hello David,
In a healthy and properly maintained engine I don't think it's that important an issue. You must not have an original WWII head if it has the bypass blank cast into it. Does the M201 head have this blank?

davem201m38 · Post by **davem201m38** » Wed Jun 03, 2009 3:49 am

Yes Wes, the M201 has blanks cast into the head and water pump. But it has the re=inforced casting for the head so it looks just like an MC head but without the machining. I think I have some photos in gallery.

It also has a flat machined surface where the MC62--- number should go.

Now I have things stripped down I should try and compare the block castings.
Yes, photo 74 of 80 in my gallery shows these blanks on an M201 engine, please check it out.

Wes, I'd be very intersted to know what you think the block casting is they used, there are several pictures in my gallery and I can send you any others.
Thanks,
Dave.

davem201m38 · Post by **davem201m38** » Wed Jun 03, 2009 3:59 am

Sorry, I was hoping the image would be bigger.