69 351W -4v running hot and pinking

Original factory M code 351, fully rebuilt with all new parts to stone stock specs plus aluminium 22" inch rad no AC. Engine only has 280 miles, runs really well but pinks when hot and gets really hot, doesn’t boil up but gets hot? My thoughts are poor quality gasoline and or the engine being new and tight? Anyone got any ideas? Many thanks!

this could be a problem in the engines timing, advanced timing will cause both issues running hot and pinging. and you need to run premium with the compression ratio on a M code engine.

Welcome to Cat community.

When is it running hot? At all times or just at idle & slow traffic or just at high speed?
Answer to this question will certainly help troubleshooting.
Overheating only at idle and/or slow traffic (while OK at high speed) is most likely caused by lack of ventilation through rad, the contrary (overheating only at high speed while OK at idle/slow traffic) is most likely caused by lack of coolant flow.
Running hot at all times may indicate bad timing/advance, bad water pump, air pocket in the cooling system ect… including bad gasoline & tight engine as you suspect!
I have personally observed regular gasoline (87 - E10) to enworse tendency of my Cat to run hot at idle/slow traffic + lead to rougher starts after standing hot at rest for a while.
Read this thread:
then scroll through the whole “Maintenance Restoration & Repair” section of this forum, you will find other threads where this has been discussed + there are experts in here that will chime in for sure. Good luck.

Thanks for your input, car will keep itself cool at speed, but slow traffic builds the heat really quickly, timing is 6 degrees as per factory! When you switch off the engine, you can feel the heat, will start again on the key just fine! Going to try some octane booster and a gallon of racing gas. Fuel really is terrible here in England, my friend has an '88 Caprice which should run on anything…pinks on regular

If your temp needle is reliable and remains about half way of full scale at idle/slow traffic for long periods of time + coolant (50/50 water/Glycol) does not boil nor spill after you turn the engine off, then I would think the heat you feel is normal as these old engines are made of heavy cast iron that can accumulate a lot heat within their bodies.
If not already done, you can increase air flow through rad at idle with a fan shroud when well configured with the blade fan, to help run cooler.
Personally, I wait at traffic lights / jams wit trans (auto FMX) in neutral position, especially in the hot days, and that helps keep the temp needle from moving upward.

Has anyone ever try an electric cooling fan? if you can find one with a tight shroud for good air flow at idle. plus with a little wiring you could set temp to turn on and run if A/C is on plus add a delay to run a few minutes after engine is shut off.


I’m jumping in a bit late, but its important to note that, stone stock, the 351W 4V has 10.7:1 compression ratio. It must have premium fuel to avoid pinging and detonation. I forget what minimum octane rating the owner’s manual recommends, but its 98 or 99, something way up there. Better than any pump gas available today. So, first thing, get some better gas and see how it does.
Second, a lean-running engine will run hotter and be more prone to pinging than one running more rich. Try richening up your fuel mixture and see if that helps. That’s a little tricky if you’re still running the stock Autolite 4300, but can be done.
Finally, newly rebuilt engines tend to run hot until they’re fully broken in. The overheating problem may resolve itself as you pile up some miles. But in the meantime, get better gas.

Octane ratings at the pump are different in different countries. In the US we use an average of two ratings, Research Octane Number (RON) and Motor Octane Number (MON). You will see this on the pump (RON + MON)/2 The RON number is typically quite a bit higher than the MON number. The octane requirements in the old owners manuals were RON numbers that were derived from leaded gas.

The whole issue is very complicated because the octane boosters being used today, like methanol, have less energy content by volume. The problem is that adding methanol actually requires you to run a richer mixture. If the carb is jetted for pure gasoline then you end up running lean and that contributes to pre ignition even though the fuel octane rating considered alone might be adequate. Running lean can cause the enige to run hot which is a huge contributor to pre ignition.

In this instance, when an engine runs cool at speed, and hot at idle it means that either air flow or water flow is inadequate. The first thing to look at is the fan, fan clutch and shroud. All of these pieces need to be installed and operating correctly. Keep in mind that these cars were not defective as designed by the factory. It took extreme conditions like driving across the Mohave Desert If you can get back to the original design in good working order you should be in good shape.

If everything is in place, the first thing to look at is the fan clutch. If the fan spins with no resistance when the engine is hot it is a pretty sure sign the fan clutch is bad. Occasionally you ill find that the impeller on the water pump is badly rusted and missing parts. It might still work some at higher RPM’s but not so well at idle. A few pictures of what you have would help a bunch.