Smoking Isuzu

I recently picked up a 1991 Isuzu Rodeo with the GM 3.1L V6 with TBI. It seems to have a strange smoking issue, though. A few seconds after you start it up, you start to get little puffs of smoke that mostly looks white, but against some backgrounds looks blueish. Intermittently, there will be a medium-sized puff of it that will come out when you step on the gas, but sometimes nothing. If you drive the truck around town, it’ll do this all day, but if you drive it even only a couple of miles at highway speeds, it’ll clear right up and be fine until you turn the truck off and let it sit for a few hours. Oh, and the thermostat does seem to be working, since the temp gauge gets up to normal operating temperature in city driving.

When I first saw the smoke, I figured head gasket, so I did a compression check. All six cylinders are pretty close to each other and the plugs all look normal. There’s no bubbling or exhaust smell in the coolant and I just changed the oil and there’s no sign of coolant there. It doesn’t quite seem like a classic head gasket to me since the smoke doesn’t look like blown head gasket smoke I’ve seen before and it clears up and there’s no other symptoms. Anyone have any insights or alternative explainations?

For some reason, possibly the weather, the smoke looked a lot bluer today. So I checked all the PCV lines and lo and behold I found the nipple where the PCV tube goes into the throttle body was mostly plugged with sludgy stuff. I cleared it out and gave everything a good clean and so far I haven’t seen any more smoke. Fingers crossed!

Could be the problem. Could also be worn valve guides. They produce smoke just as you’ve described.