I'm getting ready to replace the hoses and "**** water" valve on my 240's heater core.

I'm going to pressure test it somehow before I go to all the trouble of installing new parts.  My question is, does the heater core build up as much pressure as the radiator after I shut the car down?  I know the radiator cap will blow off if I loosen it while hot.  I'm on the fence about hooking it back up knowing there's a high pressure, high temp bomb behind my radio.

Thanks for any help. 

 

As long as the heater core is part of the cooling system plumbing, the pressure will be the same everywhere - radiator, hoses, thermostat, ...etc.  Absolutely get that core pressure tested just as you would with the radiator.  A good radiator shop should be able to clean and test it properly.

The pressure should be the same throughout the system.   When you pressure test it, the system should be cold, and don't pressurize it beyond 13 or 14 lbs.  (normal system pressure)

3 hours ago, S30Driver said:

The pressure should be the same throughout the system.   When you pressure test it, the system should be cold, and don't pressurize it beyond 13 or 14 lbs.  (normal system pressure)

personally i would check it higher, just to be sure it wont fail at 13-14 psi

I just went through this last spring. I bought a NOS aftermarket heater core off ebay to replace my leaker. But before I put the replacement in. I pressure tested it on the bench.

I would run it higher than the release pressure on the cap, but I wouldn't take it over about 20 psi. Over 20 and you start to bulge the end caps out. I think if you keep it in the high teens, you should be OK.

As for my heater core saga... The NOS replacement held pressure overnight on the bench, so I swapped it into position in the car. Drove like that this past summer, and by the end of the summer, the new one that I just put in was leaking.   Farqing bastages.

I'm a little worried about those lousy cork-soakers tendency to leak.  I've already bought the parts so I'll give it a shought but if it leaks, I'm done with it. 

I want to be done with it too. In fact, I'm so sick of the heater core stuff that I've been working on an alternative for my 77. I didn't mention it before because the project isn't done yet, but I just jumper the gun and started a thread about it.

http://www.classiczcars.com/topic/56726-heater-core-alternative-escort-core-into-260280/

Unfortunately, I have no 240 experience and no idea if something like this would work on your 240. Want to send me a  240 heater box for experimentation? 

5 hours ago, Captain Obvious said:

Unfortunately, I have no 240 experience and no idea if something like this would work on your 240. Want to send me a  240 heater box for experimentation? 

Be careful what you wish for Captain,  Zup probably has 10 of them -  only outdone by rear sway bars & flat top carbs. 

Thanks but no thanks.  If it leaks, it's over. 

I'll run the hoses through the firewall to look normal then put in a copper or brass 90 connecting them beside the valve on the passenger's side floorboard. I do need to get rid of those to holes in the firewall and reconnect all that to the cylinder head.  I have that all plugged off now and I believe it will run cooler coming off the rear of the head to the hose under the spark plugs.  2 months a year it's cold enough for heat and it's garaged so no frost on the windshield. 

I'm pretty sure my water kock valve was leaking when I bought the car so hopefully it will fix right up for a year or two. 

I'm guilty of  "over simpifying" (thanks ZH for the new word).   After a mock-up assembly of the hoses and kock valve I learned something.  When that valve is closed there is nothing getting past it to the heater core from the cylinder head.  So until the valve is opened up the coolant is dead headed coming off the cylinder head.  No need for another valve to stop the flow of coolant through the cabin in warmer weather like I was thinking here,

 

The vacuum cawk, if you have one, also closes the coolant supply off completely at certain settings.  Weird how complicated Nissan made their system.

I'm sorry Dave, I'm afraid I can't do that.

I think the coolant supply is shut off for you when the A/C is enabled. I guess the designers decided that we all weren't smart enough to move the temp slider ourselves.