The Stovebolt Site Forums The Shop Area Engine Shop Need some real "old" advice...

I had a ride in a 1942 Chev Canadian Military Pattern truck this weekend and at one point during a rough off road ride the driver openned a small door in the dog house engine cover...."to open the valve that releases the steam in the back of the 216 head"..... just been flabergasted!!!

At the back of the head....where the mechanical water heat sensor fit to the head ..... it seems the head has a large brass adapter with a T fitting and valve which is connected to the top of the expansion tank of the rad..... once opened it vents to the tank/rad and allows for more even cooling of the engine...... on top of the adaptor the mechanical sensor is treaded in the brass fitting.....

How critical is that plumbing???? has any civilian 216 or later 235 ..261 ever had that special venting arrangement???

I am installing a 261 in a 1940 military truck and wonder if I will need such a connection....
All the 1958 GM shop manuals make no such reference......

Would it be only for very severe service such as climbing/decending very steep hills under load????

I was amazed at what the old 216 could do...it lead the convoy in muddy roads and more modern equipment got stuck behind him.... got hi-centered once but someone remarked that only 2 wheels were spinning.... red faced the driver had forgotten to engage the 4x4 drive..... slow has hell but it got there.....

So how strange-weird is that steam valve????

Bob C.

The best place to ask this question is probably www.g503.com In fact, I think this was discussed recently. Anwyay, the 302 gmc in the M135 and M211 also has a bypass hose from the rear of the head but since it is plumbed to the thermostat housing it does not have a valve. I'm sure that you could do something similar with the 261 to improve cooling.

Thanks Jason

I have never been to g503 thanks for introducing me to a new source of info.

sounds like only the military with there over design/overbuilt ever worried about a steam relief valve. I may occasinally drive my truck in rough off road but doubt it if I will ever pull a limber and artillery piece up the side of a mountain for fun.

Still I am curious as to the practical application or necessity of such a contraption.

Any other comments or suggestions are welcome.

Bob C.

Just a guess, but since so many things were in short supply during the war it may have been difficult to get coolant... thus the need for a little extra engineering.

I could be wrong!

Don't forget that WWII was during the transition from alcohol to ethylene glycol as antifreeze. I don't know what was available during that time frame, but I would bet that both were in short supply.

Also, the 261 (and the big cube small blocks) have steam passages from the block to the heads which are not there in the 235/216 engines.

Interesting observation/comment Fred.... the 216 did not have steam holes from block to head....

For some reason they seemed to trap heat/steam in the upper recesses of the head..... and of course steam is not a good coolant as liquid water is...

According to the GM 1942 military shop manuals the military was privileged with the early ethelene glycol antifreeze similar to today's brew but no doubt not as exotic. They relied on single weight oil for the crankcase and added gasoline or kerosene to the crtankaces before shutting down the engine to dilute the viscosity.
On start up you were instructed to fast idle for 30 minutes to boil off the dilution liquids(gas or kerosene) before getting under way and/or pulling heavy loads. Dilution rate of 8 ounces at 0F and 16 ounces at -40F....

...and trucks had no heaters....initially... then they got wise and retro fitted a lot of them...

By the way the line venting to the Rad tank varied from 1/8 copper to 3/8 rubber hose.... some with a 1/4 turn valve and others without.

If I can find all the right brass fittings, I may plumb my 261 to look more like the old 216....

Any other suggestions or pratical experience with that contraption?????

Bob C.