First few runs after engine rebuild and she over heats
Hey guys,

I spent all day today with my father n law troubleshooting why the engine gets so high when I drive it for about 20 minutes. The needle goes to about 80% or just before high. We checked that the thermostat opens up by removing it and putting it in boiling water. We also switched from a 180 to 160 thermostat so it opens up at a lower temperature. With the 160 thermostat in, we confirmed water pump works by seeing the water move with radiator cap off. We also noticed that its burps (bubbles) about every 3 seconds when she is high. Someone at the auto store told us that it is trapped air and so we removed the temperature sending unit, filled radiator with anifreeze until she spilled out of the sending unit outlet, and then put the sending unit back in. Now she doesn't bubble/burp but the temperature still climbs to about 80% of high. Question is if this is normal after a rebuild? I remember on another thread that someone mentioned their thermostat going past the 50% point as well.

This is kind of a long post. Sorry about that. Slightly higher operating temps are normal for new engines. Also the 69 factory 4 barrel 351W has high compression by todays standards, 10.7:1. Higher compression = more power but also higher engine temps. The bubbles stopping is a good sign.

Many things can cause high engine temps. I will try to start with easy and inexpensive.

Does it get warm for all driving conditions? Or only low speed (less that 25-30 mph) or only high speed? Low speed only heating issues are typically lack of airflow through the radiator. High speed only heating issues are typically insufficient radiator capacity or poor water flow. Ignition timing also influences engine temps. Lean air fuel mixtures also increase engine operating temps.

1) The first simplest item is check the base ignition timing, mechanical advance, and vacuum advance (if you use one). Retarded ignition timing will cause higher engine temps. People typically run 10 to 12 deg BTDC base timing for these motors. It's a bit of trial and error. If its at the stock 6 deg. BTDC advance it to 9 or 10 deg. BTDC. Drive it, see if it pings (detonation), and see if it cranks okay when hot. [But, if your starter is the original stock style, it will likely need to replaced soon with a small high torque permanent magnet style starter because the header heat tends to ruin the stock original style starter.] These motors need premium fuel. So make certain there is premium fuel in it if it pings (detonation).

2) *** The next simplest thing is install a high flow thermostat like Mr. Gasket, EMP Stewart, and others offer. These make a bigger difference that you would expect. This in itself might lower the operating temps. If you only have a standard thermostat be certain it has a bleed hole in it. If not, drill a 1/8" bleed hole in the outer non moving portion of it. Position the bleed hole toward the top when installed. This helps purge air and balance the pressure on both sides of the thermostat.

3) What size radiator does it have? The 69 and 70 models were notorious for having undersized radiators. For a copper/brass radiator at minimum the larger 24" wide radiator with 3 rows of tubes. Even on a non A/C car. I ultimately ended up with the largest aluminum radiator Griffin offers. Expensive, but it helps a lot.

4) What size fan does it have? The stock 5 blade is minimal and often is insufficient. I will say, from my experience, for aftermarket fans Derale offers better quality fans than Flex-A-Lite. At least you will not cut your hands on Derale's flex fans.

5) A fan shroud is a must regardless of the radiator size.

Good luck and let us know what happens.


I just measured the fan as 20"w x 18"l. The timing is about 10 BTDC. I had 6 but she runs better at 10. I'm also looking into an electronic ignition because the points are giving me trouble. I just replaced the ignition points and condenser. She starts fine on about the first dozen times then gives me trouble again even after new points.

I agree, these motors never ran good at 6 deg BTDC.

When you mention it gives you trouble starting after about a dozen times, does it crank slow or crank fine and just won't start?

The 20" x 18" dimensions sound like the radiator width and height, is that correct? If so, that is unfortunately the smallest width and height size offered in a 69 Mach 1. I would seriously consider upgrading the radiator to the larger 24 inch wide saddle mount style with a fan shroud. Whether or not it needs it. If you look through National Parts Depot's catalog or website you will see the different radiator sizes available for these cars.

Keep in mind the factory tach will need to be retrofit to operate with an electronic ignition system. And Ford has that pesky resistor wire that needs to be bypassed. If you go with MSD, they offer a tach adapter so the stock tack will function. The only down side is the adapter's don't last very long and are relatively expensive.

The fun begins!! What is first, ignition system, cooling system, high torque permanent magnet starter?


That is the radiator dimensions. Ok I gave the smaller size. She cranks fine but won't start unless I play with it (check point gap & timing). They were fine last I checked.

Also do you recommend pertronix or msd system? My plan would be to buy the whole kit. For pertronix it would be flame ignitor ii and blaster ii. Or msd 6a. I do not have a lot of knowledge yet on the differences between the two comparing like for like. I know msd comes with a box and pertronix doesnt.

(08-03-2015, 08:42 PM)rindel Wrote: That is the radiator dimensions. Ok I gave the smaller size. She cranks fine but won't start unless I play with it (check point gap & timing). They were fine last I checked.

Also do you recommend pertronix or msd system? My plan would be to buy the whole kit. For pertronix it would be flame ignitor ii and blaster ii. Or msd 6a. I do not have a lot of knowledge yet on the differences between the two comparing like for like. I know msd comes with a box and pertronix doesnt.

All the things listed above are worth looking into. 1 other thing giving you problems as mentioned before,could be you are running too lean, this will cause overheating esspecially if the motors tolerences are reuduced as in a rebuild.
A lean condition will also give you starting and heating problems especially if the timings out as well- so check all your vac hoses blanks,and manifold gaskets for leaks, and of course spark plug color.

It sounds like no spark when it won't start. Just a thought, on old Ford points distributors its common to have to replace the wire from the negative side of the coil to the points, (Primary Wire). The tend to break internally inside the distributor from years of bending as the advance system moves.

MSD vs Petronix is tough question to answer. MSD has been around longer, their stuff is really more performance oriented, but Petronix looks more OEM after installed.

I'll give you my preference but it's ultimately your choice. Your car would be fine with either one. I use MSD. There were few others around when I purchased it. But I would still use it today. I will add, the MSD small base Pro-Billet distributor, P/N 8578, fits the best. MSD offers an adapter to fit a larger dist cap on it which I suggest. Depending on intake manifold, since the other distributors MSD offers are taller there can potentially be fitment issues with the air cleaner.

The Petronix makes a more OEM looking installation. It looks easier to install. But even with the Petronix you need to work under the dash to bypass the original resistor wire.

With MSD there is a Tach adapter which provides some potential to get your factory tachometer to work without retrofitting it.

Your decision, myself, of those two, I like MSD so I'll sacrifice the less original look and spend more time installing it. If MSD, consider a box that has a rev limiter in case you ever would like that option.

noroz makes a good point on running too lean. With a stock ignition system there should be some color on the spark plugs. I would check them a few times to be safe. I don't think the Edelbrock 600 cfm carbs have a history of running rich. Also, make certain the carb is not percolating and flooding the engine causing the hard start. Edelbrock carbs are notorious for doing that. But mostly when on an aluminum intake manifold with an unblocked heat cross over passage. Edelbrock's tech section even discussed this condition.

One final note (for now) on the two aftermarket distributors. MSD uses the old reliable Ford Duraspark type magnetic pick-up and the desirable GM style mechanical advance setup. The mechanical advance is accessed merely by removing the rotor and is easily adjusted. MSD also includes graphs with advance curves to eliminate trial and error methods. Petronix may be the same, I don't know. Maybe somebody with more Petronix experience will chime in.

Best Regards,

This is a little off topic. But if you like original Ford performance parts here is an alimunum intake on Ebay for a 351W.

These were sold through Ford parts departments. I've seen them plain like this one, some are embossed with FORD block letters and some are embossed with SHELBY block letters. It looks good, but there are no pictures of the bottom. The price is actually the lowest I've seen for these. It has 8-bolts per side like you original 1969 cylinder heads. Just thought I'd throw it out there.


For the hard start issue, you mentioned the tach no longer works. These factory tachs can fail resulting in a no start condition (no spark). Since the tach doesn't work it might be worthwhile to unplug it and install a jumper wire across the two connector terminals on the harness side (not the tach side). You should be able to get to it from under the dash. This would eliminate the tach as the possible cause for no spark.


My alternator cable had a black wire that was broken off. I have no idea where this wire connects to but figured it was a ground and connected it to chassis. I found out that I have the alternator harness with tach (3 male plugs plus one female) but only three wires connected. Now I'm thinking this wire is part of the plug. I dont think this will fix my tachometer because all the online info says the positive side of coil feeds the tach (also info from you guys). But then why does my alternator harness say with tach? I know this is a long shot but puzzling. Anyway I will connect the black wire to the harness plug this week.

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