Less VACUUM when Cold...normal?

Question

In July, I had a nice AutoMeter Vacuum Gauge installed in my 1990 Grand Prix.

I live in Ontario, and the weather is starting to get cooler, especially in the mornings when I go to work. This past week, it's been about 45-50 degrees F' when I first start the car, compared to the normal 70+ degrees F' it's been for the past couple months.

Anyways, I've noticed that my engines vacuum is 3" hg LESS than when the weather was HOT out. Also, the hotter the engine gets, the more vacuum my engine produces. It's normally 18-19" hg at idle but is now about 15" hg when COLD.

I'm just a little worried that I may have an intake gasket leak or something that swells/closes when it gets HOT. I'm wondering if when the weather here REALLY gets COLD, like 30 degrees below 0, I may find EVEN lower vacuum numbers and reduced performance/reliability.

Anyone with some input?

THANKS!:)

Mike Romain · Accepted Answer

There is an easy check...Get some carb cleaner spray and spray it around the gaskets and vacuumhose fittings when cold.  If the idle changes, you have the leak nailed.Mike86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '0088 Cherokee 235 BFG AT'sOldsFan4Ever wrote:

Steve · Answer

Thicker oil requires more power from the engine to maintain idle RPM. Idle air control lets in more intake air to keep the idle up, hence the lower vacuum reading until the engine warms up and the oil thins out.

Less VACUUM when Cold...normal?

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