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Topic: Exhaust manifold temps

in Forum: C3 Engines


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Exhaust manifold temps (1/3)
 10/11/15 4:45pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1406

So while playing around with my carb, I decided to play with my laser temp gauge.  Pointed it at the manifolds near where each exhaust port is.  They all read somewhere between 380 and 410 at idle, except for the number 2 exhaust.  It reads around 290 to 310.  What could cause that?  This is after the car has been running or driven.  It idles and drives with the normal smoothness of a carbed engine.


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Re: Exhaust manifold temps (2/3)
 10/12/15 11:08am
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


Joined: 12/2/2003
Posts: 6424

The cooler cylinder is firing, but not as well as the other cylinders.  You may not feel it, there may not be a miss, but there is a power loss.

This could be a partial misfire due to a spark plug, wire, slight vacuum leak, all the usual suspects.  It could also be weak compression in that cylinder.  I would do an ignition inspection, and while you have the plugs out do a compression test on the entire engine.  Don't do just one cylinder, you want a good comparison between cylinders.   Let us know what you find and we go from there.
Re: Exhaust manifold temps (3/3)
 10/12/15 6:39pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1406

It has new wires and plugs, and I had am MSD electronic dist. and spark box installed years ago.

I'm wondering if the airflow from the fan is better over the front of that manifold than the driver side and that is taking some of the heat off the surface of the manifold.  I'll try removing the fan and see what temp I get when it gets to normal temp (and before it overheats Shocked).


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