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DanLewis
Jedi Trainee
Offline
I finally figured out why my Bugeye has been overheating, and I thought I'd share in case someone else has the same problem.
When driving and air was being forced through the radiator, the engine temp would sit at or just above 180F (the thermostat setting). However, at idle the engine temp would climb to 200F even on a day when the outside temp was 75F. The radiator had been flushed and filled with 15% antifreeze and a bottle of Redline's Water Wetter, the air/fuel mixture was actually running a bit rich, and the timing had been set properly, so you can imagine why I was puzzled.
About two months ago I had replaced the tired old 948 with a 1275. The old engine never overheated, so I figured it had to be something related to the engine swap. At first I thought that the original downflow radiator just wasn't up to the task of cooling the 1275, but that turned out not to be the case.
Today I read an article that I'm sure many of you have seen: "Timing and Vacuum Advance 101" by John Hinckley (https://www.camaros.org/pdf/timing101.pdf). He points out that lean mixtures take longer to burn than rich mixtures, and "at idle, the engine needs additional spark advance in order to fire the lean (and exhaust-diluted) idle fuel/air mixture earlier in the cycle ..." Later he states, "Anyone with a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling..."
That last part about idle cooling caught my attention: When I did the engine swap, I had also installed a new electronic distributor with only mechanical advance - no vacuum advance. So I put the old distributor (with vacuum advance) back in, set the timing, and voila - no more overheating at idle! The added bonus is that the engine temp when cruising now stays right at 180F. That's because cruising also uses a lean mixture and high manifold vacuum.
I hope that helps someone who has been struggling with the same problem. Now I need to edit my signature line (done).
Dan
When driving and air was being forced through the radiator, the engine temp would sit at or just above 180F (the thermostat setting). However, at idle the engine temp would climb to 200F even on a day when the outside temp was 75F. The radiator had been flushed and filled with 15% antifreeze and a bottle of Redline's Water Wetter, the air/fuel mixture was actually running a bit rich, and the timing had been set properly, so you can imagine why I was puzzled.
About two months ago I had replaced the tired old 948 with a 1275. The old engine never overheated, so I figured it had to be something related to the engine swap. At first I thought that the original downflow radiator just wasn't up to the task of cooling the 1275, but that turned out not to be the case.
Today I read an article that I'm sure many of you have seen: "Timing and Vacuum Advance 101" by John Hinckley (https://www.camaros.org/pdf/timing101.pdf). He points out that lean mixtures take longer to burn than rich mixtures, and "at idle, the engine needs additional spark advance in order to fire the lean (and exhaust-diluted) idle fuel/air mixture earlier in the cycle ..." Later he states, "Anyone with a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling..."
That last part about idle cooling caught my attention: When I did the engine swap, I had also installed a new electronic distributor with only mechanical advance - no vacuum advance. So I put the old distributor (with vacuum advance) back in, set the timing, and voila - no more overheating at idle! The added bonus is that the engine temp when cruising now stays right at 180F. That's because cruising also uses a lean mixture and high manifold vacuum.
I hope that helps someone who has been struggling with the same problem. Now I need to edit my signature line (done).
Dan
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