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smoke under the hood

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May 24, 2016, 6:20 PM

Post #1 of 5 (896 views)
smoke under the hood Sign In

My wife is driving a 97 blazer with a 4.3. There is a small amount of burnt smelling smoke
coming from back around the distibutor after she drives about 10 miles coming home from

I pulled the filler cap off to see if any smoke came out of the crankcase. It has a
o-ring on it and seals tight when you put it on. No smoke came out but I could tell tht
there was a little pressure in the crankcase that come out when the cap came off and the motor
idle changed a little.

It has plenty of oil.

There is no oil dripping on the driveway.

I crawled under it and I did not see where any oil had been burnt on the exhaust pipe. She said the oil
pressure is about 5 pounds higher than it normally is. It was 40 when I looked at it but she
said it was 60 until she drove it about 5 miles.

I think it may be coming out of the crankcase but I really have no idea where it is coming from.
It is smoking enough that you can see a haze and she says she can see smoke coming from out
of the crack between the hook and the windshield.

Anybody got any ideas as to what is causing this smoke?

She is worried about the oil pressure too. I told
It never dropped below 60 when she was driving down the highway.
It was 40 setting there idling in the driveway. She wonders if the oil pressure is a problem.

I thought maybe the oil pressure sending unit had a crack in it. I figure that the leak may be small and the oil that leaks out must be burning up on a hot exhaust manifold or exhaust pipe and dropping on the driveway. A bad sending unit would also explain the oil pressure too. I can't figure out where it is mounted. I would
appreaciate someone telling me where it is and any other advice as to what to look for.

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 24, 2016, 6:39 PM

Post #2 of 5 (895 views)
Re: smoke under the hood Sign In

It sounds like you have an oil leak that is dripping onto the exhaust. You need to get the car up on a lift and look for the oil stain on the exhaust.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

May 24, 2016, 11:13 PM

Post #3 of 5 (880 views)
Re: smoke under the hood Sign In

Need to look harder for the leak as HT suggested.

It doesn't take much oil on a hot part to make a show of smoke and could easily not drip to ground.

You said it had pressure when you took off oil cap? Inconclusive on that. Can check at the dipstick better for a very slight vacuum and if not PCV isn't overcoming blow-by if all things normal not really a surprise for a near 20 year old engine.

There's oil mist throughout crankcase being inhaled by PCV or should and if pressure will find the weakest spot to push a drip out anywhere it's sealed.

Oil pressure observations are normal - did anyone think it would stay at 60? Not at idle - oil type and engine temp and wear dependent totally.

Back: Seeing smoke when hood closed there should be evidence found fairly easily then why is next. Need to find this IMO, smoke that bad for any reason if burning off of hot exhaust really can catch fire so a must fix,


Ultimate Carjunky / Moderator
Discretesignals profile image

May 25, 2016, 4:27 AM

Post #4 of 5 (871 views)
Re: smoke under the hood Sign In

Oil pressure sensor is right by the distributor.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


May 25, 2016, 9:27 AM

Post #5 of 5 (858 views)
Re: smoke under the hood Sign In

Thanks for telling me the oil pressure is ok.

I only have about 45k on the shortblock and tranny. I got it from my son who bought it primarily because it had just had the shortblock installed by Firestone and they also overhauled the tranny too. He offered the lady $800 and she took it.

She said she was tired of spending money on it and it still needs some work and maybe you can fix it up yourself.

He needed the money so I gave him $2500 which was the kbb value for it. Probably too much but he is my son and I was helping him out. I think he got a good deal on the flip.

I just wanted some good transportation. I knew it was going to be a project. I replaced all the sensors, fuel pressure pump, water pump and the spyder. I also had to replace the rear bumper and paint the hood and fender because the lady had replaced them because she had got into a wreck.

I did what HT told me to. I got it up in the air to check for leaks. The motor and tranny are clean. There does not appear
to be a leak from the rear seal or anywhere else.

I also got up under the hood back over the distributor and the oil pressure sending unit/switch
does not appear to be leaking. I was able to get my hand all the way around it and it was clean

So, God only knows why that smoke was coming from. I suspect since the ac was running that the water was dripping off
the accumulator and getting on the valve cover washing dirt and water on to the exhaust manifold.

I went ahead and replaced the pvc valve. The old one was not stuck and still rattled ok and you could blow
through it. So I don't think it was bad but I replaced it anyway. I guess the spring might be bad.

If it starts smoking again I will get back under it and maybe then I can figure out why it is smoking.

Go ahead and close this I think I got it now. Thank you and HT for the help.

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