different header temps cause for concern?

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rigger3006

rigger3006

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decided to put heat sensor gun on headers after a drive, they all averaged in the 5 to 600 f range except #4, it was 290 f., plug looks good, valve action seems normal. was wondering what could cause such a difference. and vacuum was a steady 16 degrees.oh ya, 318. should i be concerned?
 
Swap a couple plug wire, see if the low temp moves
 
At idle #4 is still about tha same difference, definitely lower, changed plug and plug wire, still the same
 
time for a compression check........
could have a air leak, like a intake manifold gasket leak, in that cyl.
 
Compressions same as others, avg 135, vac gauge is steady, would that rule out intake leak?
 
Is this low temp only at idle or can you hold it at say 2500 and re check
 
Hmmm confused.
If you had a vac leak, a 2200 it would go away.(High idle without the choke activated aka partially closed...Right?)
If compression is the same between cyl then you don't have a bad valve/rings.
Are you sure your temp gauge/gun can get a good reading on that header tube?
 
Cudafever said:
Hmmm confused.
If you had a vac leak, a 2200 it would go away.(High idle without the choke activated aka partially closed...Right?)
If compression is the same between cyl then you don't have a bad valve/rings.
Are you sure your temp gauge/gun can get a good reading on that header tube?
Click to expand...
 
Very easy for temp reading, about 1/4 " from header flange on all cylinders, would a leakdown test help? I dont have s tester though
 
rigger3006 said:
Very easy for temp reading, about 1/4 " from header flange on all cylinders, would a leakdown test help? I dont have s tester though
Click to expand...
It wouldn't hurt!
just thinking out, in, Far, Left, Field......it's like the cam has one lobe or two ground differently.
If you had a cooler cyl on each bank aka left and right side of motor, then i would blame the Carb.
 
Also reset air fuel mixture with vac gauge, could be the cam, new summit 6901, maybe 8 hrs on it
 
rigger3006 said:
Compressions same as others, avg 135, vac gauge is steady, would that rule out intake leak?
Click to expand...
No. Cylinder will pull air in anyway it can. I would retorque intake and see if that helps. You could be pulling air in from the bottom of the intake port (crankcase air). This would lean that cylinder and should lower EGT on that cylinder IMO.
 
Did you actually do a leak down test? or just a pump up test with a gauge? We have seen a non-sealing valve do this exact same thing on the dyno. Customer somehow rolled the cam over in the block when changing a timing set, "kissed" 4 pistons with the valves. bent 8 of them. Surprisingly only robbed about 10 HP. BUT...EGT on those 4 pistons was down. Then we did a leak down, and found 8 leaky valves.
 
Dont have a leakdown tester, placed an order from jegs yesterday, it was a tossup between tester and cam degree kit, cam degree kit won
 
retorqued intake, at high idle tempswereall in 600 range , at idle no.4 started cooling off compared to others, about 150 lower in temp. gonna try a few other things today and see what i can figure out
 
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