Thread: Overheating Mystery

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Please don’t misinterpret, I’m not trying to tell you what you should do, rather what my experience was.

IMHO, I will suggest you should do some testing on your motor:

1). Does your motor over heat a idle (stopped) as well as on the highway (cruising)? If only at idle, more than likely you do not have enough low speed air flow (fan). If both, you need to test further.
2). Check your total timing, make sure your mechanical and vacuum advance are working properly. I would suggest total timing be between 32°-36° and all in by 2500rpm (vacuum advance disconnected at this time). If you have vacuum advance check to see how much it adds at idle and cruise rpm (I would suggest 10°-12° vacuum advance max). Timing will cause heating problems.
3). Use your timing light on each wire at the spark plug, it will tell you if spark is getting to the plug (light will flash), a miss can cause over heating.
4). Pull the plugs keeping them in order as to which cylinder they came from and examine them. The plugs will tell you a lot about your motor’s condition and keeping them in order will show which cylinder is suspicious.
5). While the plugs are out do a compression test, verify all cylinders are within 10% of each other and compression is sufficient to support combustion. If you have two adjacent cylinders with lower compression (especially 3&5, 4&6 on SBC), usually this indicates a head gasket, you can squirt a little oil in these cylinders and re-test their compression to see if the rings are a problem (the oil will raise the compression by momentarily sealing the rings).
6). While the plugs are out, check valve adjustment. Poorly adjusted valves can cause low compression and heating problems.
7). Check the air/fuel ratio, a lean motor runs hot. Some smog check stations will test the air/fuel ratio reasonably for you.
8). Check the flow rate through your radiator, with the cap off, warm your motor to thermostat opening while watching the flow, when the thermostat opens you should see a significant change in water flow. Put the cap on and feel the upper and lower hoses (careful hot), the upper hose should feel firmer than the lower. If both feel firm, you probably have too much restriction, check for a clogged hose or passage.
9). If you suspect an exhaust blockage, un-cap your headers and run to see if it corrects problem.

Again just my opinion and suggestions, not trying to tell you what or what not to do, or insult anyone, simply trying to help you find the problem.