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My 1970 Mach 1 overheats when sitting in traffic or after exiting the freeway. If I'm driving it seems fine. I've replaced the radiator, clutch and fan, 180* thermostat, hoses, temp sending unit and checked that the gauge is accurate with an infrared heat gun. The gauge sits in the middle with the heat gun reading around 185-195. Once it gets up to the H the car starts to stall and it boiled over once. The heat gun reads around 235-240 on the intake manifold at this point. So the gauge seems pretty accurate.

I can idle on the side of the road for about 45 minutes before it gets overly hot, less if I run the A/C. This makes me think the thermostat and water pump are working properly as I assume it would overheat much faster if the water wasn't flowing well.

I took it to a specialty shop today and spoke with the owner. He said i've done most of the easy stuff that usually fixes the small problems. There are a few minor "outer" things he will check like the exhaust and hoses, stuff like that. After that it gets expensive and involves taking the engine out and working on that. Sometimes they find the problems, sometimes not. He's had a couple clients where they just couldn't find out what the problem was. One guy decided to live with it and another guy had them put in a whole new engine.

He said if they ended up having to get into the engine and tearing it apart it'd probably be around 12-15 hours for labor. Then parts on top of that; plus the charge for the machine shop if they need to do any actually milling on the engine. So likely $1500-$2000. Or they might find something simple is plugged up and could fix it in a couple hours. He just can't say ahead of time.

So, my question to you guys is have I missed anything "simple" that I can do myself before resorting to taking the engine out? I've been given suggestions of putting in electric fans, though that seems more of a 'masking the problem' type fix. Any help would be great as trying to fix this problem is starting to push me over my budget.
Maybe check the timing and make sure the vacuum advance is working properly on the distributor.

Good luck and keep us posted if you resolve the problem.
Are you running a fan shroud? Is the fan the correct distance from the radiator? Is it a 3 flue copper radiator?
http://midamericachevelles.com/Fan_Clutch_Adjust.pdf

http://www.chevelles.com/forums/showthread.php?t=389234 read posts

http://www.arrowheadradiator.com/14_rule...obiles.htm
Yes, I have a fan shroud with the fan half in, half out. The fan sits about 1" from the radiator, which I'm told is about right. I didn't know you could adjust the fan clutch. I'll take a look at that. Also, it's a standard duty clutch. Would a heavy duty clutch be better?

The radiator is a 3 row, 25" (width) aluminum one from Champion.

The engine does need to be timed but I've been told that'll maybe save me 10*. Currently I'm hitting temps of 240* so even with that savings I'll still be overheating. However it's on the list.

Regarding the vacuum advance, is there any difference in having it hooked up to the ported vacuum vs the manifold vacuum? Currently it's hooked up to the ported vacuum.
I have read lots about ported vs. manifold vacuum to distributor.
I have mine hooked ported. the idea, I think was full vacuum at idle increased timing at idle, and when you accelerate that retards timing to prevent spark knock.
I am an old mechanic, and I was taught that timing should increase on acceleration.

read this, it is for GM, but will apply to fords also.
2nd post
http://www.bangshift.com/forum/showthrea...um-advance

OK, after reading this article, I am going to try the non-ported ...full vacuum on my car...never too old to learn. I will set initial timing at 8 degrees and hook up the full vacuum hose to dizzy. I'll drive it and see what happens.
Ah yes, I saw that article a few days ago. It seemed to explain the differences and make arguments the best. I also read other posts that said they always use the ported side so it almost seems like you have to try both and go with the one that works best for your situation. The article at least convinced me to try it and see what happens. I can always change it back if it doesn't help.

I'm thinking there might be several solutions that when all are put together they'll give me the temperature decrease I'm looking for. Right now I'm shooting for timing, using the manifold vacuum on the dizzy and am going to have the shop check the engine block and exhaust system for clogs and debris.

Also, this morning I tried to check the flow of the coolant in the radiator to determine if my water pump is working properly. I let it heat up with the cap off and when the upper hose got hot (thermostat open) the coolant started moving around gently. It definitely didn't flow very much. Should I see noticeably strong movement at idle if the pump is working well?
My work truck was doing the samething ,after trying most of the same stuff I did a exhaust check at the rad. Found a small crack in a head gasket. just a guess.
Has the motor been rebuilt ? Bored out to the max ? The first thing to do is psi check the system with a pump & gauge. If it doesn't hold then try to find the leak. If it does hold then I'd knock the rear freeze plugs out if it hasn't ever been rebuilt. See if the rear of the block is starting to get packed full of crap before tearing the motor down. I've seen some so packed it was a pia to even get the freeze plug out.
I did a pressure test and it held pressure fine.

The engine was rebuilt 2 owners ago (about 4-5 years ago). The previous owner only put about 500 miles on it and said it always overheated on him. I'll check the freeze plugs. One of the rebuilders I talked to said it's possible some stuff got in there during the rebuild or they just might not have done a good job putting it back together.

Sure sounds like blocked passages since it was a problem from the get go.
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