My 68 442 tends to have an overflow problem from the radiator from time to time. In fact I would say its intermittent. I decided to replace my original four core with an aluminum radiator from cold case and it cools better than the original four core, to just see if that would resolve my issue. The original radiator would run around 190-195 and this new one is running around 160-165. The engine is a 455 stock. I did not completely rebuild the engine but instead I replace the water pump,fan clutch, replace the oil pump and timing chain and changed the fuel pump. The car has not ran hot just the overflow issue from time to time. I timed the engine @ 12 BTDC. On my 72 442 which has the same engine I have never experienced an overflow problem with it and it has the original four core in it.
The 68 has the rally pack on it and the temperature gauge never gets to the half way point. I thought just maybe the engine might have a air lock in the the coolant but not sure that is the case.
Any suggestions is much appreciated.

Thanks in advance
Gary

 

Normally this is an indication of a bad radiator cap or your over filling the radiator.

 

Thanks Eric
I will drain some of the coolant from the radiator because it has a new cap and see if that solves my problem.

 

You can and should run a quick simple test. When the engine gets to operating temperature, coolant should be traversing the radiator and engine. The upper radiator hose should be firm, not easily collapsed by your hand. Squeeze the upper radiator hose once the engine gets to operating temperature. If it's mushy and collapses easily coolant is most likely NOT being circulated through the engine and instead is boiling over from the radiator.

 

If the coolant is boiling, that will increase pressure in the system and make the upper hose hard. That's why coolant is lost - the system exceeds the pressure cap rating (15 psi or so) and vents out the overflow tube.

 

If the coolant in the radiator is boiling and not moving through the engine the upper radiator hose will never be hard. There will be no increase in pressure if there is a leak in the system such as a failed radiator cap. A failed radiator cap and any other leak in the system will not increase the pressure it will decrease the pressure.

 

You're correct with respect to the notion of the pressure exceeding the rated pressure of the radiator cap. However, if the radiator cap is not performing at it's designed pressure rating, or it's sitting there loose, cracked, broken valve, busted radiator hose, vent **** cracked, another form of leak, the system won't build pressure enough to push fluid into the engine and instead can finds it's way out the radiator overflow, as well from simply boiling out w/o making it into the engine. Often times while the engine is running and the vehicle is being driven, the fan and air movement will abate the increase in temperature. Turn off the engine in the garage and most often you'll witness a puddle of coolant. I believe both scenarios are likely.

 

I once had a water pump failure, the impeller rusted off the pump shaft, so no coolant flow at all. Boilover occurred within a few minutes, with a super hard upper hose and coolant venting out the overflow port.

 

I may be misinterpreting what you are saying, but a failed radiator cap will not prevent coolant from circulating through the system. The water pump does that. A failed radiator cap will result in a lower (or higher if stuck closed) operating pressure, which will lower (or raise if stuck) the boiling point of the coolant. That would then make coolant more likely to boil inside the engine (there is no heat generation in the radiator to cause it to boil there).

 

I am seriously not understanding what you mean by this. Coolant will flow with the cap completely removed (zero pressure build up in the system).

 

You got it Bubba. If you lower the pressure of the closed system water will boil at a LOWER temperature than what it is designed to operate. Yes, the water pump will move water, but is it moving water of the designed pressure is what I am eluding to. The water should be at a maximum pressure of 16 psi for a closed system designed to operate @ 16 psi. And, yes the water is beginning to boil inside the engine and it changes phases from liquid to vapor and the vapor will then condense inside the radiator where the temperature is cooler - augmenting and enticing an overflow condition inside the radiator. If there is less than the designed operating psi w/in the radiator the radiator will boil over.

 

Yes, the only reason the system is moving water is because the impeller is moving the water, but it doesn't demonstrate the system is operating under pressure. Again, a "simple" test to determine if the system is moving under "pressure" is to squeeze the upper radiator hose. It's not definitive, it's a simple test.

 

Norm
I did perform that test and the upper hose is hard at operating temperature. I just let the car run at idle for about 25 minutes and I measured the temperature with my digital temperature gauge and it read 165.4 at the highest. I might not have been clear when I indicated the overflow, but it would only happen after I shut the engine off and as I mentioned it was an at times situation. I hate intermittent problems. I did drain some of the coolant as Eric had suggested. I plan on driving the car about 30 miles tomorrow to test it out and will let you guys know if the problem still exist. Also I adjusted the idle speed down to about 700 where I previously had it at about 825.
I really appreciate everyone's suggestions.

Gary

 

I have had several conditions exactly the same as yours on several cars of this age - faulty radiator cap every single time - FWIW, it doesn't matter if it's brand new out of the box, some are complete duds. Sometimes (most often) the upper radiator hose was easy to collapse.

 

Kenneth, that was in fact a complete FUBAR statement on my part. Typed faster than thinking it through. Yes, the pressure is not pushing any fluid through the system it is only the impeller which is moving the liquid.