The impeller on some water pumps can come off the hub with no external
clues. I saw this happen once on an early 70's Ford 300" six - the
impeller was spot welded (if I remember right from 20+ years ago) to the
hub somehow. I kinda doubt the old Chevy pump is built this way,
however.
There may be some debris in your cooling system that blocks the
thermostat intermittently. A full flushing might help. Had this happen
on a '66 Buick, shortly after I'd poured in some radiator "Stop Leak";
found a big chunk of it in the thermostat housing. That's the last time
I used that crap.
The vacuum advance motion all occurs inside the distributor. The point
plate moves relative to the housing, position controlled by the vacuum
advance mechanism. Incorrect timing either way can contribute to
overheating. If you connect your vacuum source (mouth or whatever) to
the distributor with engine running you'll get an engine speed increase
as you increase the vacuum if the system is working. If you do it with
the cap off you'll see how it works.
Another thing to check if you think the timing might be off is the
centrifugal advance mechanism (I believe the 235 has one; most engines
do). You'll find it under the point plate; it'll be 2 fly weights with
springs that move the point cam relative to the shaft as shaft speed
changes. The weight pivots can wear, the springs can break, the whole
thing can get so gummed up it doesn't work, or worse it'll be
intermittent. Some guys lock it out and run an extra 200 or so static
timing so they know exactly what the total timing is , but it makes for
hard starting and maybe pinging. The quick way to check is, with the
cap off turn the rotor in the advance direction; you should be able to
turn it about 200 against the springs then hit the advance stop. When
you let go it should return cleanly to the retard stop. Repeat, repeat;
it should be absolutely repeatable. If not, get the point plate,
springs and weights out and fix whatever you find wrong.
Rob, I had your Zen moment as my screen saver at work for quite a while
until I found a better one:
EARTH FIRST!!! We'll mine the other planets later...
Bill Gray
william.gray@snet.net
-----Original Message-----
From: owner-oletrucks@autox.team.net
[mailto:owner-oletrucks@autox.team.net] On Behalf Of Rob J.
Sent: Thursday, January 17, 2002 11:37 AM
To: _Oletrucks
Subject: [oletrucks] overheating problem
My truck ('49 w/ 235) has started to experience overheating problems.
It would get up to almost 212 (pegged out to the right) as it warmed up,
then would fall to around 190...but sometimes, I would have to turn it
off and coast till the air flow reduced the coolant enough. At idle, it
will not overheat, but still runs a bit higher than normal (around 190).
I figured that maybe the radiator had stopped flowing properly, or that
maybe the thermostat had stopped working properly, so last night, I took
a radiator I had that had been tested by a rad. shop as being good, and
put in a new 180 deg. thermostat (they didn't have any 160 or 170s as
that would have been my preference). I also have a new 7psi rad. cap on
the system.
But even after doing all that, I am still having the same heating
troubles. I thought that maybe I have a cracked head or blown head
gasket, but I changed the oil...no water in the oil and no white smoke.
I'll do a full compression test and vacuum tests this weekend, but
doesn't seem that either of those are happening.
The only things that I can think of that might still be at fault: 1) is
it possible for a water pump to stop spinning without there being some
external evidence of that? I would think there would be some noise, or
wobble, or leaking, but water pump seems fine externally (after changing
the thermostat, I put my finger in the cold rad. into the water as it
warmed up, and as it hit 180, the water turned hot, but I did not notice
anything that I would call a "flow" or appreciable movement of the
water, so I'm assuming the thermostat is doing its job, but should I not
be able to see a "flow"? I don't recall ever checking this when
everything was working right, so don't really have anything to compare
to (ie. normal vs. abnormal). 2) the only other thing I saw that could
I suppose be affecting this...as I was warming the engine up, and with
me under the hood, I revved the engine, but did not see the dist. rotate
at all (vacuum advance). Should it not rotate such that I would see
this externally (or does all the movement occur internally without the
outside rotating)? Tonight I will pull the cap and hook a vacuum source
up the the line and pull a vacuum and see what is happening. If it
turns out the vacuum advance is not working, couldn't that cause an
overhot situation at cruising speed, that might not show up at idle?
TIA,
Rob
My Zen Moment for the Day: Do not walk behind me, for I may not lead.
Do not walk ahead of me, for I may not follow. Do not walk beside me,
either. Leave me the hell alone! oletrucks is devoted to Chevy and GM
trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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