I have a '69 427/400 numbers matching roadster and a problem has arisen that has me scratching my head. The car has an after market aluminum radiator and has always run at about 190 degrees since I restored it, some 12 years ago. Recently, it has begun to blow the upper radiator hose off (where it attaches to the intake manifold). The car continues to run cool when it's being driven, but 4 or 5 minutes after I shut it off...bang, off comes the hose. In the last 12 months, I have replaced the heater hoses, radiator hoses, the expansion tank ( one of the nipples was corroded and broken off), the hose between the top of the radiator and the expansion tank, the expansion tank cap (15 lb.), and the thermostat. There are no leaks and I don't believe that I'm losing coolant and the oil does not appear to have coolant in it. Incidentally, I did have the intake and the thermostat housing powder coated and I'm wondering if the powder coating on the thermostat housing (where the radiator hose attaches) is slippery enough to cause the problem. If you are familiar with the reproduction aluminum thermostat housings for this engine you know that they have barely any lip at the end to keep the clamp from sliding off. Lastly, the car has about 4000 miles on it since the restoration was completed in 2003. I would really appreciate any input from people who may have an idea that I have yet to think about. Thanks

 

Hi md,
Welcome! First Post!
Perhaps a quick check would be to 'rough-up' the powder coating using course sand-paper on the surface of the neck where the hose contacts it.
This would eliminate the 'slippery' possibility.
I would also check the inside of the hose at that point too in order to insure it's not 'glazed'.
Regards,
Alan

 

Thanks for the quick reply, Alan. I've ordered a replacement thermostat housing from JEGS. It's not exact, but it seems to have a better "lip" than the exact reproduction housing that I have. I should get the part by Thursday....I'll also check the inside of the hose as you suggested. I've got my fingers crossed that the fix will be that simple. Just wondering if anyone else has experienced this problem

Nick

 

I wonder if the pressure release on the rad cap is not working correctly. Just borrow another cap from a different car.

 

Does the aftermarket aluminum radiator have a filler neck or just a tube running to the expansion tank?

 

Thanks for the reply. The cap was checked out and it released at 15 lbs.
Nick

 

It just has a tube that is connected to the expansion tank by a rubber hose.

 

I think at this point you have eliminated every other possibility other than the coating on the neck.

 

A couple of friends have suggested that it might be a blockage in the radiator, something that is keeping the pressure from escaping into the expansion tank...so I guess I'll check that out next.

 

only blockage point could be the small pipe on the radiator that connects to the tank otherwise you would have overheating when running. Remove the hose on a cold engine and start it, if coolant comes out the small pipe no blockage.

 

I've put a stiff wire into the radiator where the small hose to the expansion tank attaches...and there was no blockage for a few inches into the radiator. What's also interesting is that I had the car running in the driveway ( for about 15 minutes) the other day...the temp. was reading about 190 degrees....and sometime before I shut the car down, a fairly substantial amount of coolant came out of the expansion tank overflow on to the driveway. The tank didn't appear to be over-filled prior to starting the car. Lastly, I'm just not sure that 15 psi could blow that hose off. irrespective of the powder coat. I really appreciate the suggestions, and will, of course, try them all.


Nick

 

double check your heater hose at the heater core,,they may have bent enough to restrict flow

 

Thanks, Tom. I've already checked that and have replaced the heater hoses (they were 12 years old) last month...there were no kinks. My concern is that if I just replace the powder coated thermostat housing with a non-coated one (or one with a larger "lip") and that wasn't the problem, I may end up causing a rupture somewhere else..like the heater coil, for instance. I think, to be safe, I'll have the radiator checked out first and then change the thermostat housing. Thanks for your reply.


Nick

 

It may be a new cap but I would test it with a gauge

 

I'm not sure if your 400 expansion tank is the same as my 435 tank. Is the hose from the radiator going to the port on the tank and not to the port under the cap?

 

There is probably nothing wrong here, other than you are overfilling it and the thermostat outlet/hose needs to be replaced. Your engine is running at normal temp. The expansion tank is belching out fluid when the engine is turned off to let you know it is overfilled. Don't refill it, allow it to equilibrate.

Change the powdered coated thermostat housing. It is blowing out at less than 15 PSI...The system is designed to release at 15 PSI, the cap sets the blowoff. Your hose is blowing at less than 15.

 

Did that...a friend of mine has a tester.


Nick

 

Hi, 3x2, I believe the tanks are identical and the hose goes to the neck of the tank just under the cap.

 

Hi bellaireroad, the tank is not belching fluid when the car is turned off...it did it when the car was running. The problem is that when the car is.... turned off.... the upper radiator hose blows off rather than venting pressure to the expansion tank and then out via the cap and overflow hose. I think that you (and some of the other members who have responded) may be right about the powder coated thermostat housing. What's interesting, though, is that this problem didn't occur until after 2 months of driving the car after I intstalled the powder coated intake and thermostat housing. I think that I'll pull the radiator this weekend and after having it checked out and flushed, I'll replace the thermostat housing and keep my fingers crossed. Thanks for the reply.

 

Are you saying the hose from the small tube on the radiator is connected to the neck of the expansion tank? Is the link below the tank you have? The neck pipe is for overflow, the bottom pipe is for the radiator.
http://www.dewitts.com/collections/a...rge-tank-brass