Hey guys, have done plenty of searches trying to figure it out, but have come to the conclusion that my problem is fairly specific... I've recently bought a 1988 TN Magna, is on Gas and in good condition! Does not overheat, doesn't misfire etc, one of few problems I have noticed (the more troubling one I would say) is that when cruising downhill the car tends to blow quite a bit of white smoke. It does not blow any smoke at any other time... Would there be any reason for this?

Thanks guys
Ben

White smoke is usually water vapour coming out of an exhaust system. Probably won't happen on a warm day. If the car isn't using coolant its nothing to worry about. If the car is a manual you can always put it in neutral going down hill . . . . .
If it does use coolant it might be cylinder head trouble. Mate had a Sigma that spat water drops and steam out the exhaust all the time, turned out the head was soft and a valve guide had moved, letting coolant straight into the exhaust system. New head fixed that.

Pull the plugs and look for red rusty crusty bits on one or 2 plugs , that's coolant being burnt in a cylinder! If they all look the same you can stop worrying. Its the easiest way to tell if you have a problem really. Let us know how you go.

Sounds more like valve stem seals. Leave it to idle for a while and give a good rev, see if you get any then

If the car is a manual you can always put it in neutral going down hill . . . . .

Definately NOT the best thing to do!!

Maybe a few things to check:
- Is your oil a nice oil colour (that is, not milky)
- Is your radiator water a nice coolant colour (again not milky)
- Are you using coolant? the coolant is a sealed system, any loss of coolant is a sign of a leak somewhere either internally (bad) or externally (good, in the sense of it being able to be fixed).

If i had a LPG system i'd be using the following:
http://www.flashlube.com/en/electronicvalvesaverkit/index.html

check you oil level, if its too full, the oil may rush forwards and get blowback or something similar and end up mixing with air and fuel in the cylindar causing it to blow smoke. This is ofcourse it the smoke is actually smoke, not steam, and if it only does it on a downward slope.

otherwise, if it is smoke, it will probably be the valve stem seals like madmagna said. if the car ir really old it may be rings, but this would generally make it blow smoke continually.

Sounds more like valve stem seals. Leave it to idle for a while and give a good rev, see if you get any then

Yep, Agree here... Also, you could try coasting down a hill, (No Accelerator), then step on the Accelerator at the Bottom of the Hill, and look out for Smoke!!

Cool, will try all suggestions and report back. Thanks heaps for your input guys

if the stem seals are worn they will leak in high vac situations... like idle, or deceleration...

also check your PCV, and or crank case breather hoses.. if they are blocked (usually with gummy oily sludge) they could be causing a build of of crank case pressure.. but you would usually see smoke during normal driving a little if that was the case...

if your stem seals arn't completely F'ed you might be able to temp fix them with a bottle of seal conditioner/worn engine treatment... this is only a band aid... but sometimes can work... the best stuff i've used in 300km + corolla's is Liqui Moly engine resealer... but the stem seals were only just starting leak... yours might be too far gone