HELP - coolant overflow on 1969 318

[gwilson09]

I recently replaced the original radiator with a newer radiator out of a 69 Polara 383 with AC. New rad has 13 psi cap and all new hoses. Did not change thermostat or water pump. There is no overflow tank, just a rubber line going from the cap down the side of the radiator and emptying on the ground. I'm in Texas and it is HOT here. Triple digits most days. After about a week of driving (10 mi a day to and from work round trip) the radiator is nearly dry. There are no leaks and there is water or sludge in the oil.

Did the Sweptlines originally come with overflow tanks? Anybody got a picture of one? I'm not sure what to do next.

[Dood]

Did the Sweptlines originally come with overflow tanks? Anybody got a picture of one? I'm not sure what to do next.

Mine doesn't have one. Just a tube that ran down the driver side of the radiator and spills out on my driveway every time I over fill the thing. It leaves a tell tale droplets at its outlet if I crawl under there and look.

I think I have a 7 psi cap on my stock (though recored) rad. I didn't see any PSI specs in my FSM for the '67/'68 in section 7, though it was a quick look. Could that cap be too high pressure and forcing your coolant out? When you say it is dry, you mean dry to the bottom of the upper reservoir? Is the petcock secure? Also, could it be that your block was completely drained recently and you have had to refill the core and the rad?

[gwilson09]

Yeah, not bone dry, but I have to add a gallon of water plus a little more. I saw on another thread that the recommended psi rating for a cap is 7. The only caps I have seen for sale are in the 12 to 18 psi range. So, a lower psi cap would be better than higher? That goes against what I would think, but I'm not particularly learned in this particular area. I'm probably ging to swap the thermostat and water pump soon. Any idea where to check for a 7 psi cap?

[Dood]

As I understand it, you want to match the pressure to the characteristics of system. Given the non-stock rad, I don't know how that will all work for your setup.

A radiator's cap is intended to pressurize the system relative to ambient thereby raising the boiling point of the coolant. If the pressure is too high, however, it will blow your coolant out the overflow. If it is too low or non-existant, the coolant could boil. To perform the regulated pressure function, it has a relief valve calibrated roughly (i.e. +- 1 psi) to the rated pressure, e.g. 7 psi. For older overflow systems I think we want lower PSI than the newer overflow recycling reservoir ones.

To determine if your pressure was too high, empirically, you could probably rig a catch can to the overflow and that's where all your coolant is going... Maybe someone has a simpler idea. Caps are pretty cheap, though.

I checked Napa, O'Rielly's an Autozone online and they all seem to have 7 psi caps available and the last two recommend it for my '68 318. Amazon has a Stant 7 psi for ~ $8 (Prime eligible). One funny thing about Amazon is that they show you what people 'also buy with this item', in this case, with the 7 psi cap:

Customers buy this item with Stant 10229 Radiator Cap - 13 PSI by Stant $5.41

So it seems people like to buy and try multiple psi caps in one order?

As an aside, although the heat capacity of a 50/50 ethylene glycol / h2o mix is slightly lower than straight h2o, the EG will offer a higher boiling point, better rust prevention and lubricate the water pump. So, I try to top off with 50/50 antifreeze/water rather than straight distilled water, when possible.

[F6866]

I went to Advance Auto and for 10 or 12 bucks bought an overflow kit, mounted it on the fenderwell with a fabricated bracket and haven't had to add coolant since.

[Hobcobble]

I recently replaced the original radiator with a newer radiator out of a 69 Polara 383 with AC. New rad has 13 psi cap and all new hoses.

Did you have this Polara rad checked out in any way?
Seeing as its "technically" the same age as the
original rad from your truck, you might not have
gained any ground unless you know for certain
that this Polara rad is clean and flowing as new.
Things might look good from the top and the
cores might appear dry & undamaged from the
outside but there's a lot that might not be known
about the "innards"....

The 7psi cap is standard on [at least] '68 and
earlier 100/200 trucks. Perhaps someone with
a later FSM can look for data for your specific
year. I've had great luck running 185F
thermostats in my Sweptlines. Maybe someone
with a FSM can confirm the recommended
thermostat for your '69.

Do you have the shroud that attaches to the
core support and lays over the top of the rad?
This piece helps keep air flowing where it should.

How far from your rad is the fan? How many blades
does you fan have? Is it stock or something else?
Did your truck come originally equipped with a fan
shroud?

Is your engine timing a bit too advanced? What do
you know about the inside of the engine block? Did
you ever change core plugs on it and get the chance
to clean out all the built up sludge in the lower extremities
of the block? Have you ever pulled the block drain plugs
[each side down by the oil pan] to let old coolant out?
I've pulled these on old engines to find out that NOTHING
pours out due to a build up in the lower block.

What water to anti-freeze ratio are you using?

John

[gww]

the radiator is nearly dry. There are no leaks and there is (((( water or sludge in the oil. )))))
. have you had the cap off while running? looking for compression in cooling system? or pressurize the rad and check for leak down. head gasket or poss. cracked head?

[gwilson09]

Many thanks to all for the replies.

The radiator is actually new, but I wasn't very clear about that, so there's no way it's clogged. There is a fan shroud in place and this radiator sits in nearly the same place as the original. The five-gladed fan sits approximately three to four inches from the radiator. The top, rubber-y cowl piece is long gone, so I'll need to look into getting something into place there. Unfortunately, I don't know much about the inside of the block. It's an old truck that I only got in October, 2009. It's my daily driver and a project, as well. The original radiator was, shall we say, hole-y, but I never had a problem driving around with it only half-full and leaking. I guess that may point to a pressure issue?

[gwilson09]

CORRECTION: I just noticed in my initial post that I said there is water or sludge in the oil. There is actually NO water or sludge in the oil. Picked up a Stant 7 psi cap today and will see how that works. Regarding looking for movement of water in the radiator: Will there be movement if the thermostat is closed? More movement when it's open, I assume?

[Hobcobble]

Many thanks to all for the replies.

The radiator is actually new, but I wasn't very clear about that, so there's no way it's clogged. There is a fan shroud in place and this radiator sits in nearly the same place as the original. The five-gladed fan sits approximately three to four inches from the radiator. The top, rubber-y cowl piece is long gone, so I'll need to look into getting something into place there. Unfortunately, I don't know much about the inside of the block. It's an old truck that I only got in October, 2009. It's my daily driver and a project, as well. The original radiator was, shall we say, hole-y, but I never had a problem driving around with it only half-full and leaking. I guess that may point to a pressure issue?

Did you have the fan off of the water pump when
you swapped out rads? If so, did you make sure
your fan wasn't flipped over and installed backwards?
Just checking.... The fans on my sweptlines
don't get much further than 1.5-2 inches from the rad.
If you have an old inner tube laying around, you can
fashion yourself a top tank shroud.

If need be, you can drain the coolant and pop out the
rear core plugs on the engine block. I'm pretty sure
you'd have enough room to tap in new ones without
too much difficulty. A lot of scale, sludge, etc. tends
to settle rearward in the engine block around cylinders
7 & 8. I've hoed out gobs of crap from a few engines
when replacing the core [soft] plugs.

Another trick to try is drilling a small [3/32-1/8] hole
in the flange portion of your thermostat. This allows
the coolant system to "burp" itself and will help
alleviate any possible air pocket problems.
John