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scj 428 overheating

scj 428 overheating

Joined: January 12th, 2015, 7:22 am

January 12th, 2015, 7:43 am #1

I can really use some help with this one. I'm the original owner of a 1970 Mustang convertible powered by a super cobra jet 428.. I have always had low speed overheating, for example in parades and long traffic jams, but I now have an additional problem.
While using a LED temp probe I found my engine has 7 cylinders with about 350-375 degrees exhaust port temps, but the back one on the passenger is reading between 850-900 degrees. This is at about 900 RPMS. and I caannot find out why?
The engine has been gone through and has TRW forged aluminum pistons that are dished 28 CCs to lower the compression to a nominal 9.5-1. Using Edelbrock aluminum heads and waterpump, a 67 Ford 428 HP aluminum intake (This is the one Ford used to later mold the 428 cast iron one) MSD ignition, and the cam is a Comp 270-290, also using an aluminum radiator.
I have checked everything I can imagine, compression is steady at 155 in all cylinders, the cam lift has been checked with dial indictor and is OK.
I think the problem may be in the exhaust manifold only, but any suggestions are gladly excepted.
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Joined: February 16th, 2015, 5:18 pm

February 17th, 2015, 2:53 am #2

Exhaust manifold temps on carbureted engines at idle shouldn't be trusted. The engine should be brought up to a resonable operating speed, preferably under load - then look at the temps. What do the spark plugs look like? If they're good I don't know if much credence should be put in the idle manifold temps.

I'm not real smart on FE's and don't want to insult you, but have all the baics been checked? Thermostat? Purge air out of block, heads, and intake manifold? Correct gaskets on the build? Using the radiator/fan shroud? Is the clutch fan pulling air at low RPM? Upper radiator hose temp versus lower radiator hose temp?

I'd like to talk to you about the engine - I'm going to build my CJ and I can use advice.

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Joined: February 24th, 2005, 2:02 am

December 5th, 2015, 8:39 am #3

I can really use some help with this one. I'm the original owner of a 1970 Mustang convertible powered by a super cobra jet 428.. I have always had low speed overheating, for example in parades and long traffic jams, but I now have an additional problem.
While using a LED temp probe I found my engine has 7 cylinders with about 350-375 degrees exhaust port temps, but the back one on the passenger is reading between 850-900 degrees. This is at about 900 RPMS. and I caannot find out why?
The engine has been gone through and has TRW forged aluminum pistons that are dished 28 CCs to lower the compression to a nominal 9.5-1. Using Edelbrock aluminum heads and waterpump, a 67 Ford 428 HP aluminum intake (This is the one Ford used to later mold the 428 cast iron one) MSD ignition, and the cam is a Comp 270-290, also using an aluminum radiator.
I have checked everything I can imagine, compression is steady at 155 in all cylinders, the cam lift has been checked with dial indictor and is OK.
I think the problem may be in the exhaust manifold only, but any suggestions are gladly excepted.
To add to the previous response, the FE exhaust manifold is kept cool by being directly clamped to the cylinder head. Some "rebuild kits" provide thick exhaust manifold gaskets, but these nightmare gaskets "insulate" the exhaust manifold from the cylinder head, preventing the exhaust manifold from releasing heat energy to the coolant in the cylinder head, and causing them to warp or crack.

Thick FE exhaust gaskets are only appropriate for steel-tube headers, as steel can handle higher temperatures than cast iron. Cast iron gets soft when overheated. As always, note that many FE heads have high-exit exhaust ports, most 1966-later heads have low-exit "unibody compatible" ports, and a few 1966-later heads have neither.

The "factory original" way the FE exhaust manifold was clamped to the head (not sure about CJ/SCJ) was to either use an embossed soft steel shim gasket, or to use no gasket at all. This kept the exhaust manifold cool. The embossed steel shims are probably extinct, as I've not seen any new ones for decades. Nowadays, some folk find good luck using a very thin layer of copper-silicone applied to the face of the manifold, as the copper helps conduct heat out of the manifold and into the cooling system, while never getting hot enough to degrade the silicone. I've not tried to use silicone on an exhaust manifold yet. I find freshly surfaced exhaust manifolds clamp productively to the cylinder head.

The "hot spot" you've found at the corner cylinder might have something to do with a rusty mating surface at that location, helping insulate the manifold from the head. Fortunately, the rear cylinder is well-immersed in coolant, so I don't suspect the head is getting hot.

As an alternate theory (and not at all likely to cause your kind of single-cylinder temperature), the passenger head gasket may be on backward, preventing coolant flow behind the #4 cylinder. Fortunately, FE head gaskets have a visible "tab" which can be easily seen when peering under the hood. As long as that head-gasket "orientation tab" is properly positioned, you know the head gasket is installed correctly.

JMO,
Shoe.
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Joined: February 24th, 2005, 2:02 am

December 5th, 2015, 8:57 am #4

I didn't realize the Wild West forum had become so inactive. I just noticed many of these posts are "dated" long ago. I do hope answers to these older questions were found over at FordFE.com or other good FE forums.

I want to elaborate on my odd statement, "and a few 1966-later heads have neither" in my previous post. By "neither", I refer to the few FE cylinder heads cast from 1966 (C6AE-R, etc.) which have low-ceiling and high-floor exhaust ports, making them "centered" ports which are a bit smaller than the high-exit and low-exit ports. Never fear, as the smaller "center ports" have real performance potential, as the "low ceiling" is present only at the port face, not inside the runner, and the material is readily "ground-out" of the head to produce a nice-flowing high-exit exhaust port that performs very well.

Shoe.
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