> Well, I am absolutely and totally at a loss as to what is wrong. During the
> breakin, I followed the advice I've always heard as to how to break in an
> engine, ie. to run it up to around 2000 rpms, and let it sit there for 15-20
> minutes. So I did that. Everything seemed to go pretty normal. The temp
> gradually got up to 190 or so (no thermostat yet installed), and held there.
> I didn't see any small bubbles during this time and just before the end of
> the 20 minutes, I put the radiator cap on. BUT, as I reached the end of the
> break in, and as I reduced the rpms to idle, all of a sudden the water from
> the radiator started spewing (with sufficient force to shoot to the fender)
> out under pressure out of the overflow tube at the filler neck (cap is a
> zero pressure cap). I immediately shut down the engine, and looked inside
> the radiator and saw nothing of concern. I started the engine again and
> gradually added water so it wouldn't be hit with a large volume of cold
> water at once. That went fine, but at idle, I am seeing the same damn small
> bubbles!
Where to start.....
Again, I'm not used to working on the older vehicles, but I do work
on cars a lot. Its not uncommon to have bubbles popping up after
you first fill the coolant system. There's always air pockets trapped in
there that take some time to blead out. First off, I'd highly suggest
putting the T-stat in before going any further. I can't swear about the
235, but some motors are very touchy about not having a T-stat in
place. Causes excessive flow and doesn't allow the coolant to
absorb heat, or dissapate it (I know, it sounds silly, but I've seen it happen).
Second, could have overheating as you discribe from a really big air
bubble. I wouldn't think these trucks should be hard to blead, but anything
is possible. Theres some things to check to find out if this is a possibility.
Make sure you have good flow on the water pump. There is an easy
test for this. Start the engine with the radiator cap off. At an idle
with the coolant filled to the top, rev the engine quickly. If the water
pump is working well, the fluid will drop quickly as you rev it up, and
when you chop the throttle, you should have a little gyeser coming out.
This also assumes that you don't have any restrictions in the system.
As the engine is warming up, make sure you have near-equal temps
on the upper and lower radiator hoses. Shouldn't be more than....say
40 degree's. If you don't have one of those laser temp sensor thingies....
I know they are a little spendy, but man they make this type of problem
so much easier to quantify....If there is a huge temp difference, you could
have a plug up radiator, or uneffective water pump, or really big air bubble.
Most radiator shops will flow check a radiator for real cheap. If you have
any doubts about the radiator, have it checked.
If it really is just an air bubble (hard to believe with the T-stat out, but
then
that could be part of the problem as I said earlier) Sometimes
they can be difficult. For complex coolant systems on modern cars, sometimes
there's nothing you can do other than keep running it, rev'ing it, shutting it
off when it gets too hot, and repeat. Sometimes it can take over 30 minutes
to get it to finally burp....I wish I had a better answer than that for yah....
>From what little I know, the 235 did have problems with cracking heads/
blowing head gaskets (my 57' did that). I assume you replaced the head
with the rest of the engine? Was the head magnafluxed?
Ryan
rlangford@attbi.com
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
|