White smoke from exhaust.

[Dusklegend]

Hello, I am new here as I have come with a seemingly big problem with my 1993 GMC safari. V6 4.3L. When i start up my car I will sometimes get white smoke and when it happens my car will tend to idle extremley rough, this randomly started occuring this friday after it rained, I was told it can be moisture but the problem has been pursisting. Any suggestions or way to test if it is my head gasket?

[Jasen]

Have you checked to oil, does it look like a chocolate milkshake, if you look into the radiator do you see bubbles, does your coolant seem to disappear with no signs of leaking onto the ground.

[Dusklegend]

The oil looks fine, how do i check for bubbles in my radiator? Does my car have to be on? and no my collant dosn't "Dissappear" I have a leak of something in my car not sure if it is the coolant or what.

[chevymaher]

Open the radiator cap. Start it. If it has bubbles consistently, When it is full, it is a leaking head gasket. A big bubble every few seconds.
If not that does not exclude a head gasket leak. When you start it and there is white smoke. Smell it. Oil is unmistakable, Water is just that vapor. It will run rough till it spits all the water out.

[Phantom]

93 has a vacuum modulator on the trans , check to see if there is moisture inside the vacuum hose , if there is the diaphragm in the modulator has a leak and sucking trans fluid out of trans and burning it , if the modulator is leaking it will get worse , it will also give white smoke if burning fluid in small amounts , or it could be a leaking intake gasket allowing water to seep in

[Dusklegend]

All right i will give the radiator a check once I get done with some stuff here in a bit, if it is a gasket, how hard is it to replace?

[chevymaher]

Not so bad to replace just awkward working.

[Dusklegend]

Just checked and there was no bubbling. Opened the cap, turned on the car and let it go for a while watching it, all that happened was the coolant rised.

[chevymaher]

That is normal untill the T-Stat opens.

[Dusklegend]

so if there is no bubbbles then what other methods to diagnose?

[chevymaher]

Pressure test the radiator/coolant system. See if it holding pressure.

[Dusklegend]

where can I find the exact intructions to do that

[trapper20]

you just need a pressure tester, you hook it up where the cap goes and pump some pressure into the system and see if it stays consistent

[Dusklegend]

Are they expensive? And maybe is there an attachment for an air compressor?

[Phantom]

The tester can be expensive if you buy one , at least $100 probably more , but most Radiator shops will do the test for free . Just fill system up the tester has a cap on it that tightens onto the radiator and you just pump up the pressure with the pump handle , it is a handle , no air line involved , pump up to 16psi and just wait for 20-30 minutes to see it it holds pressure steady , or you may see where the leaks is if it starts leaking somewhere , also stick your finger inside the tailpipe and wipe it and notice if the residue if watery or oily , it can help reveal it it is antifreeze or oil .

[Dusklegend]

Alright, and if that comes back fine and it holds pressure what else could be the problem? Phantom, you said there is a vaccum hose on the trans, but you said it would cause small ammounts and mine is pretty constant, but seems to only be in idle, on the freeway the rough-ness stops and no sign of white smoke.

[Phantom]

The vacuum modulator has a diaphragm that can have a pinhole leak or a major rupture, with a major rupture it can be as you describe , on freeway the smoke dissipates rapidly so it does not show as much , the aftermarket modulator costs only about $15 and easy to replace,it will be the only vacuum line on the transmission , at high rpm there is less vacuum so it does not suck as much fluid , idle is the higher end of vacuum Hg.(measurement )

[Dusklegend]

Where can I buy the aftermarket modulator? and will replacing the modulator be in my book for my car? or can I find video of it somewhere.

[chevymaher]

I can't find a video on U tube of a GM replacement.

[Dusklegend]

Can't seem to find it in my repair book either