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TD42 Idle Speed

Tech Talk for Nissan owners.

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Posts: 159
Joined: Tue Apr 27, 2004 12:15 pm
Location: WA

TD42 Idle Speed

Post by GQAndrew »

Have noticed lately that after a long drive when the engine is hot the oil pressure on my mechanical gauge drops to about 10 PSI at idle, but still runs well (Over 45 PSI at 2800 rpm). I noticed that the idle is also low. When starting off its sits at about 600rpm, then when it warms up it idles at about 800, then when its hot (about 30 mins of driving) it drops to about 700. However when the air con is switched on, the idle speed drops to about 600, where the gregorys manual states that the idle will increase when the air con is on :? :?

Now, is it normal for the idle speed to decrease when hot, I though that it would increase because the engine is running more efficiently.
Also, should the idle increase when the air con is on, or decrease, is it a seperate idle adjustment for the air con?

Could the idle speed be respnsible for the oil pressure dropping to 10 at idle?

Cheers
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Post by chimpboy »

Oil pressure will drop with both lower revs and with oil that is hotter, as the oil gets thinner and moves around more easily.

With most cars (never had a diesel sorry) turning on the AC does two things: 1. it pulls the revs down because of the extra load from the compressor, and 2. it lifts the revs up because a solenoid or similar mechanism gets tripped by the AC switch. The solenoid is meant to compensate for the extra load but anything from a slight increase to a slight decrease in revs would be acceptable if it doesn't affect driveability. You may be lacking in the #2 department though.

Not sure about your slower idle when hot; this is normal in lots of cars as a result of an automatic choke type mechanism that runs a richer mix and increases revs when the engine is still cold, but I couldn't say specifically about your vehicle.

Basically if your car is fine to drive, none of the things you've described would worry me at all.

Jason
This is not legal advice.
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Posts: 159
Joined: Tue Apr 27, 2004 12:15 pm
Location: WA

Post by GQAndrew »

chimpboy wrote:Not sure about your slower idle when hot; this is normal in lots of cars as a result of an automatic choke type mechanism that runs a richer mix and increases revs when the engine is still cold, but I couldn't say specifically about your vehicle.

Basically if your car is fine to drive, none of the things you've described would worry me at all.

Jason


thanks mate :)
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