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Old 02-23-2007, 09:53 AM
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what pressure cap?

HI
Im running a modified Nissan 4 cyl with 180 thermostat and 7 lb pressure cap. everytime I shut it off a little bit of coolant comes out the overflow (no catch can yet) I was going to change to a 14lb cap but a guy told me I shouldn't because the aluminum head will warp .the engine is a 1979 just had a valve job&head all checked out and just had the radiator all gone over(it had a small leak),what thermostat and pressure cap should I be running? Catch can is on list of things to do

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Old 02-23-2007, 10:20 AM
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I'd have the parts store test new caps with their tester until they found one that actually tested 15 and then I'd put it on.

Pressure cannot warp a head, overheating does.
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Old 02-23-2007, 10:38 AM
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Quote:
Originally Posted by xntrik
I'd have the parts store test new caps with their tester until they found one that actually tested 15 and then I'd put it on.

Pressure cannot warp a head, overheating does.
pressure raises the boiling point of water

i've never asked a parts store to open a package to test a new cap,they would probably tell me to go blow myself.but thats illinois for ya,not all that friendly like they are in some southern states.
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Old 02-23-2007, 03:15 PM
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I don't think yhe parts stores around here would do that either. I'll probably buy a name brand one and have faith in the factory.Anyone suggest which brands are the most reputible?
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Old 02-23-2007, 03:29 PM
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You need to look at a manual and see what pressure your Nissan system calls for...........It's probably a closed system with a puke tank, that has a lower pressure cap.........7# sounds about right.
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Old 02-23-2007, 04:52 PM
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This engine is not stock would that make a difference?
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Old 02-23-2007, 04:55 PM
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stock preassure is 10-16 # for anything made after 1980
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Old 02-23-2007, 05:00 PM
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my engine is a 79 200sx nissan,bored,bigger valves ,high lift cam ,header and 390cfm holley
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Old 02-23-2007, 05:56 PM
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Quote:
Originally Posted by nitro_baller4692

i've never asked a parts store to open a package to test a new cap,they would probably tell me to go blow myself.but thats illinois for ya,not all that friendly like they are in some southern states.
I have seen most of the major brands, Murray, Stant, etc. and 80% of them will not test very high.

The last one I bought at O'Reilly's, Murray brand, the store tested 5 to get one that tested 15. One tested almost 0, one 3 psi, two were around 11, finally the last one they had in stock tested 15.

The last Stant I bought the best I could test was 14 with the store's tester.
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Old 02-23-2007, 06:05 PM
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Well I can ask if they test them,but I still don't know for sure what pressure I should be using
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Old 02-24-2007, 02:19 AM
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Check the shop manual, buy a cap rated at the same pressure datsun used (no your mods don't really change the required pressure). Keep the receipt, take the cap to your friendly neighbourhood radiator shop and ask them to test it. If it fails, then take it back, get another and take it, along with a 6 pack to the radiator shop. Keep trying 'till you get the right one.
Those old l20 datsuns would crack heads if over heated and corrode with hard water, but if the stock system was kept in good order with approved coolant, the correct thermostat and cap, they cooled just fine.
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Old 02-24-2007, 06:38 AM
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sounds reasonable,thanks
Gary
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