1990 Nissan Pickup with vacuum problem


My 1990 Nissan pickup truck with 338,000 miles on it was sitting for two weeks with out being driven. I have owned the truck since 1994 and I regularly change the oil and have anything that breaks fixed. But I have never opened up the engine or transmission. When I started it last night I got a lot of white smoke out the exhaust. I drove it 50 miles home and almost all the way the engine ran hotter than normal, at about the 3/4 mark or higher on the guage. It usually runs at the halfway point. No white smoke this afternoon, but 100 miles round trip the truck is still running hot. I just had the coolant flushed this afternoon and the mechanic said that there appears to be a problem with the engine maintaining a vacuum. Any ideas on the problem? Does this sound like a leaky head gasket? FYI: there is no A/C installed. This is a basic 4 cyinder pickup truck.


Yes, this does sound like it may be a bad headgasket. The white smoke could have been coolant being drawn into the cylinder through the headgasket breech, vaporized, and blown out the exhaust. The hot engine could have been from hot exhaust gasses being blown through the breech into the water jacket. And the vacuum problem could be because the vacuum comes from the pistons pulling air into the cylinders with a restriction (the throttle plate etc.) in the intake path. That causes the cylinder to pull a vacuum. If the cylinder has another place to pull fluid in (air and coolant are bothe fluids) then it can affect the engine’s ability to maintain vacuum.

My suggestion is to start with a compression leakdown test. That’s a test where each cylinder is pressurized with air and tested to see if it leaks. Post back with the results.


White smoke out the exhaust right after start up is usually just condensation in the exhaust system, especially if it occurs after sitting around for a little while. The higher than normal temp could be due to a lot of reasons, not just a head gasket. Could be as simple as a radiator cap. I’d start there.


At 338k miles and considering the symptoms, the first step in a shop would be to run a compression test and go from there.


Thanks. I have a date with a reliable shop on Monday.


The mechanic who did the coolant flush thought it might be the rad. cap, too, and got a new one on and tested the vacuum again,with the same result. So we think it’s deeper than that. Thanks.


Thanks. As I replied to the first poster, I have an appt on Monday with a reliable shop. I’ll discuss all this with the mechanic. I appreciate the insight.