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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars


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Old 10-14-2006, 02:23 PM   #1
NSDCA
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coolant leaks only when car is off?

ok so my car over heated the other day, filled it up with some water and took her home. next day inspected around the water pump no signs of coolant crust around water pump. car is not leaking anymore, took off rad cap put the heater to hot and topped it off. watched the gauge go up to the middle and drove the car for a good 10 miles. parked the car looked under and nothing is leaking. no signs of over heating while i drove it. but when i shut the car off i see coolant/water dripping??? and no i did not have the AC on either.

i havnt had a chance to look under the car but when i searched i found a mixture of answers...hoses cracked, dead waterpump etc.

ive changed the waterpump before on my old 240 but im a little lost as to why it only leaks when i shut off the car.

any advice i should know????
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Old 10-14-2006, 10:51 PM   #2
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The coolant doesnt only leak out when the car is off, you just havent noticed the trail youre leaving. It might get worse when you shut the car off, since when the coolant isnt circulating it sits in the hot block and expands a lot which is probably forcing it out of wherever its leaking from at a faster pace.

There's not many places it can come from and you should be able to deduce a general area of fault based on where onto the ground your coolant is falling.

if youre leaking coolant, obviously the motor can overheat and you risk siezing the thing. so look harder.
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Old 10-15-2006, 10:47 AM   #3
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I had the same leak as well, except the coolant will dribble out while the engine was running, and leaks out a stream of coolant on the ground when engine is off. I jacked up the car, and found coolant all over my starter motor and transmission bellhousing. Found one of the coolant hose underneath the intake manifold leaking. The coolant didn't leak onto the ground while the engine was running because it was such a small leak that it got evaporated by the hot engine before it got the chance to drip on the ground. If one leaked, all the other hoses must be on its way out very soon, so I ended up replacing all the coolant hoses as maintenance. They are molded hoses, so you can only get them from the dealer.
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Old 10-15-2006, 11:07 AM   #4
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You might want to pressure test the system NOW, because this same symptom was the lead in to my car's currently being in my buddy's shop for a head gasket
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Old 10-15-2006, 01:22 PM   #5
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ok so i had a chance to get under the car. i warmed the car up and bled the system (i did see bubbles come up from where the radiator cap is). drove it around didnt over heat. put her up on jack stands and shut off the car. nothing leaks. ( it would normally start coming out as soon as i shut the car off)

so im guessing i had air in my cooling system??

my reservoir tank was empty when it over heated the other day. would that cause it to suck in air if it was empty?
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Old 10-15-2006, 01:55 PM   #6
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did you top off the coolant again? It's not going to leak if there's no more water. The coolant temp sensor will also not register because it can't sense steam. Try letting the engine idle while the car is on jackstands and look to see if you see any small leaks. You may also try having someone rev it up to 3k rpm or so, and see if you see anything. Then shut it off and keep watching the area you think it's leaking. There are like 10 or so small coolant hoses underneath the intake manifold. You may have to remove the starter and alternator to get a better look. I had to remove them to get better access to the hoses when I replaced them.
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Old 10-15-2006, 02:06 PM   #7
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no, i did not top it off again. i took off the rad cap and bled it a bit more just cause.. it didnt need to be topped off again.

but i did drive the car again and no over heating..but this time when i shut off the car... the water/coolant started coming out. so im guessing its a hose??? i guess when its warm the hose expands so it doesnt leak out? but when i shut off the car it comes out.

im pretty sure its not my water pump.

no signs of white smoke from the exhaust (thank god) i was reading about blown head gaskets.

so hopefully its just a hose.. gotta find out which one.

if anyone else has any more info i would appreciate the heads up.
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Old 10-15-2006, 02:53 PM   #8
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There's not much that can leak in the cooling system... heater core, radiator, water pump, freeze plugs, or hoses. I don't think your heater core is leaking, because it would leak inside the car and get your carpet all wet. If it's not leaking underneath the front bumper, then it must not be the radiator. You said you're pretty sure it's not the water pump, so that leaves either the freeze plugs or hoses. Although it may be possible that one of your freeze plugs are leaking, a leaking hose is more likely it, but you may have to take a closer look. I'm not sure why the coolant doesn't leak when it's running, and I thought so too with my car, but it ended up being that the coolant evaporated before it got the chance to hit the floor. Can you see any coolant leak trails underneath? The trail looks white if it got burned off. If so, try to follow the trail and find the source of the leak.

If you do end up replacing the hoses, get a hose clamp plier like this:


Those spring clamps are a PITA, and you can't even fit a regular plier up in the tight space underneath the intake manifold. Using this hose clamp plier will make your job a lot easier.
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