mrmint69

I took a friends laser thermostat gun over and did some tests. I first started the car cold and got reading as it warmed up. Not very accurate while warmed up so it didn't tell me much. I then ran the car another 5 minutes till they were good and hot and turned it off and the 4 centers ones were all 800+. The rear 2 were 600's and the front drivers side was 200+ and the passenger side only 170 and dropped to 60 degrees within 2-3 minutes while the other were 2/3 of there origional temperature. I took the laser pointer and started at the head and went toward the point they meet up. The temperature got warmer the further you got from the engine. What should i do to figure out whats wrong? What are the best and worst case scenarios? Im actually excited to find this since i have had issues since i bought the car 3 years ago and it was down on power ever since.

Jazsun

I'm not an expert but perhaps those cylinders which are obnormaly hot are burning a lean mixture. Perhaps new plugs or injectors may help.

shoebox

Test several cars, so you are not chasing your tail.

mrmint69

I don't know anyone else with an LT1 engine other than the many on here. Maybe someone else has done this test and can give me there results. I know for sure that if the car was running for 10 minutes and i turn it off and can touch one of the exhaust ports because its only 60 degrees F after a couple minutes theres something wrong. I will check the plugs & wires any issues. Thank god the plug access is so much better on these Pacesetter mids because it use to suck doing a compression check and other things on it.

mrmint69

The injectors are brand new and the plugs have less than 500 miles. I am planning on pulling the one that has the cold exhaust and checking it for damage, being loose and if the wire is good. Besides the opti and what i mentioned i wonder what other issues could cause there to be no spark.

Pontiac_97

i have one of those temp guns. my headers got to about 560* on all the primaries before the gun maxxed out. that was within 5-10 minutes of running. right where the y pipe and collectors connects was around 130ish and go a lot cooler the furthur back i went. these are with non coated headers

kylersaulsbury

also if you get really stumped try switching the affected cylinder's plugs with cylinder's that are fine. That rules out faulty sparkplugs (like parts guy drops them or something but box is undamaged so he still sells them)

mrmint69

I'm looking for answers and here is one theory. The firing order goes 1-8-4-3-6-5-7-2. I had 4 that were all about the same (800 degrees F) and they are the 4 in order 4-3-6-5. The 4 that were 200-600 Degrees F are in order with the 2 coolest ones right next to each other. Here are the temperatures using the above firing order and the temperature in its place. 200-600-800-800-800-800-600-200 and would go back to the beginning. Its looks like a pattern and i can only think the opti could cause this. I read over 100 threads about dead cylinders and many blamed the opti for this and several fixed there problem when they replaced it. My MSD Probillet is pretty new with under 1000 miles and the car ran the same before it was replaced and with the new one. I have seen way to many issues with them so maybe its the cause. Im thinking out of the box here so don't be to critical.

sbs

slowZ

or you have a bad plug or wire.

Injuneer

Its normal for the two "center" cylinders on each side (3/5, 4/6) to run hotter on the exhaust, simply because the exhaust ports are right next to each other. The entire block runs hotter in that area. For hi po engines, it isn't unusual to add a coolant system port to the block between the cylinders.

Why did you shut the engine off and measure the temperature? It would make a lot more sense to measure it while its running.

What I suspect you are using is an infra-red non-contact temp sensor, that just happens to have a laser "sight". That type of non-contact device is very sensitive to the distance from the object (the farther away, the wide the area measured) and the surface finish of the object (emissivity). Make sure you are holding it the same distance from each primary, make sure you are focusing on an area of similar finish.... not rust on one tube and bright coating on another.

mrmint69

Harbor Freight had them on sale for only $35 and it goes up to 968 degrees F. I will do some more testing with my new one. The hardest part of doing it as it warms up is by the time i get through all 8 the reading will be higher for the last as opposed to the first. What i found was if i ran the car for 5 minutes and put the laser on it the temp would drop but real slow and i could get the reading to hold relatively steady. I will use a stop watch and let it warm up exactly the same time and read a few and come back when they have cooled and do more. This way i can get the most accurate readings. Thanks Injuneer for all your help so far.

mrmint69

Here is other results i found from a search on this site.
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Here is the results with my "Individual Cylinder Fuel Trim" set to 1.00:
in degrees F
Temp Cyl Cyl Temp
510 8 ***** 7 520
525 6 *****5 525
525 4 *****3 525
485 2 *****1 490
Front
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All readings are taken about 1" from the head on the header..Keep in mind my headers are ceramic coated..Car had been running about 30mins
1- 254 F 2- 340
3- 330 4- 395
5- 370 6- 340
7- 280 8- 244

mrmint69

The others who posted there numbers have none over 525 and the one guy says he ran it for 30 minutes. I had 800+ after 7 or 8 minutes and then the laser hit the max. What causes the temp to go so high. I have coated headers so they should be cooler than most?

Sean94Z

Having gone through a similar problem, I really suggest swapping the injectors around, then the plugs and see if the problem follows. Something I noticed on my car is that there is a HUGE amount of air on the passenger side compared to the driver's side when the fans are running. This will cause the first primary on the passenger side to be cooler. I took a piece of wood and blocked that air coming through on the passenger side and found that first primary to heat up similar to the others, but still not as hot.

I agree with Injuneer that the middle cylinders will tend to be hotter, while the 4 on the outside will be cooler. I think your numbers are right in line. Are you trying to track down a problem or just playing and noticed this? I was trying to track down a wierd air fuel problem when I found my problem. I am still not sure mine is even a problem, or if I was 'just chasing my tail' ..