<TABLE cellSpacing=0 cellPadding=2 width="100%" border=0><COLGROUP><COL width=256><TBODY><TR><TD vAlign=top width="100%">Hi. Have a question about radiator caps for my 1973 F100 2WD. It has a 302 and auto tranny, NO air conditioning, power steering but manual brakes. The truck came with a 7 pound radiator cap and no overflow (just an outlet hose running from the filler cap down the side of the radiator shooting out onto the ground). I was having some overheating problems and the cap would 'sing' whenever it got too hot. So I replaced the thermostat and that brought the temperature down but it would still occasionally hum (by this I mean that steam would come out of the cap and make that 'singing/humming' noise). O.K. So I had the cap pressure tested and it was fine. The guys that tested it said if I was going to stick with the 7 lb. cap I should build an overflow for it. They also said that if I wasn't going to use an overflow that I should go with a heavier cap. So, of course, I went el cheapo and just tied/taped in a water bottle as a cheap overflow. This worked pretty good for a while but right after I put in a new water pump the 'hum/singing' came back (still don't understand that one...new pump shoulda brought down the temps). More steam from the filler cap area.



So I said screw it (no pun intended) and just put a new Stant 13 pound cap on it but left the overflow in place and continued to use it. This completely killed the escaping steam problem but about 2 weeks later my radiator explodes. I mean bad...lucky the engine didn't burn up. So anyway, I just put in a new OEM radiator (2hrs. and 165 dollars) but was wondering what the heck I should do about an overflow and a radiator cap? The new radiator came without a cap or any specs on what poundage I should use. So I just decided for now to go with the shiny new 13 lb. cap and NO overflow. I just don't wanna blow another radiator (assuming that my replacement of the 7lb. with the 13lb. had something to do with it) and was wondering what you guys think I should go with: 7lb. cap plus overflow? 7lb. and no overflow? 13lb. and no overflow? 13 lb. plus overflow? Something else?



Thanks.



P.S.-Of course it is altogether possible that I just needed a new radiator and that my problem is now fixed (I know for a fact that the old one was rusted out and on its last legs). I am just paranoid of another one blowing up.


</TD></TR><TR><TD width="100%"></TD></TR><TR><TD width="100%"></TD></TR><TR><TD vAlign=top width="100%"></TD></TR><TR><TD vAlign=top width="100%"></TD></TR></TBODY></TABLE>

 

all mine are 11-13 lbs.

my F-600 and B700/750 are 7lbs.

 

How high are you filling it ? It shouldn't be higher than the fins. If it's filled higher it will bleed it's self off. I've always ran 7 lb caps with no over flow. If it keeps doing it, I'd get the system pressure checked.

 

Can you spell "head gasket leak" ???

You should not be blowing "steam" out the cap - maybe air, but that should stop at some point, like within a few minutes. It should not do that constantly.

Sounds like you're getting cylinder pressure in the cooling system and either the block or a head is cracked or a head-gasket is leaking. Easy way to check is with one of those Stant testers, the pump with the guage on it - just put the thing on where the cap goes, start the truck and see how high the pressure goes - it shouldn't go very high, a few pounds max (7lb cap should not be venting) - put it in drive (or slide the clutch a little) to put a load on the motor and hit the gas - if the pressure jumps you have a leak between a cylinder and the cooling system.

 

I will try filling it just to the top of the fins as Mark A. suggested. I will also buy one of those Stant testers (need to have that anyway for general diagnostics) as krewat said. Thanks again guys. So far the truck has run fine the two days since I put in the new radiator (with both the 13 and 7 lb. caps...I'm gonna stick with the 7lb. for now, though). Truck just has to last me until my '91 Crown Vic arrives from Cali. (ebay purchase). Then I can tear it apart if need be. It's one of those things where even if there is a head gasket leak or something major like that I won't mind because it'll give me a legit reason to tear the thing apart and learn something new. I'm sick like that.

Thanks again.

 

The only problem with a head gasket leak is if you ARE getting combustion gasses into the cooling system, the area that is leaking will erode over time, and the block or head will need to be milled. But who knows until you pull it apart? (Or check cooling system pressure while revving it

Drive it till it drops, and if it's not pushing air out the 7lb cap anymore, I wouldn't really worry about it - strange though, having that much air coming out of it that it sounds like a pressure-cooker... and now it doesn't.

Here's a question: Where did the radiator rupture? Top or bottom?

art k.

 

Did you know you can get a Washer reservoir/coolant expansion tank combo from an 80's truck ?

That's what I'm got planned for mine.

I don't like the fact of the overflow hose to nowhere.

Btw, The coolant level should be 1" below the bottom rim on the rad cap opening of the rad.

 

Just inspected the old radiator and could not tell from that where it ruptured. As I remember the night it happened most of the steam seemed to be venting from about 2/3 to 3/4 the way down from the TOP of the radiator. Oh, and one thing...the radiator was ORIGINAL to the vehicle...which, considering that it was actually manufactured in 1972, makes it about 32 years old. Here's hoping the problem was simply a rusted out, old radiator. I'm still going to pressure test the system, however. Thanks.

 

Sounds like the old radiator might have been completely clogged... good luck with it, and MAKE SURE you let us know how it works out!

Even little things, like what pressure it ran at at idle...

 

I have had a few (5) ford trucks from 68-78 all i had put on 13lb caps and overflow containers and never had a problem leaking or overheating and actually ran cooler after the upgrade

 

overflows are not good for these rads unless you keep the bottle empty always
use it as a catch can and your fine
coolant in the bottle adds hydraulic pressure to the rad and will blow out the seam before long
I know I run a radiator/fabrication shop and have seen it on many fords

 

how come there are stickers on these rads that say do not fill unless water level is more than 4'' down

 

Since that was the original radiator and you've had overheating issues, have you had your cooling system flushed lately. If the radiator was a mess, you could still have a bunch of crap in the rest of the system that could compromise the new radiator also.

 

my 74 and 79 F-600s have a factory overflow bottle. complete with cold fill and hot fill lines.