hard starting when hot

bunch of us ran into this with our fox bodies as soon as we put our batteries in the trunk...

i threw everything in the book at this and finally found the only real cure for us was one of three options:
1) move the battery back under the hood
2) go up to a 16volt battery in the trunk to offset the additional voltage drop/use required when hot
3) go to two 12v batteries in the trunk for the same reason as going to 16v

My symptoms,..car would start fine bone cold and progressively got worse the longer time the engine ran. After 30mins of drive time it wouldn't start at all. I'd have to pull over, pop the hood, and run the fan for 15-30mins to get it cold enough to start (overcome the additional power required by the heat soaked starter to start. What i did find was that if somebody jumped me i could easily start so it was clearly a resistance/voltage issue i needed to resolve.
I started off with the largest CCA amp battery i could get from Sears. This didn't work. So I then changed all my cables over to OO welding cable not 2 gauge but 00, some seriously thick crap. This added about 5mins to the drive time before it wouldn't start. I then fabbed up a heat shield and added some fiberglass heat shiedl to the fab plate. Again this prolonged the time a few mins that i could run the negine and successfully restart but didn't alleviate the issue. I then upgrade the alternator to a 140amp and shortened the wire run as much as possible to the starte. This again only prolonged the length of time i could run with a succesful restart, but stil overall the issue persisted. I then wrapped my header with that fiberglass wrap stuff and put the fiberglass sleeve over my starte wire to keep that from soaking up heat with the same outcome as above in the previous steps. I could now run the car about 30-45mins and sucessfully restart but the engine turned over reallllllly slow. after an hour forget it or in the summer it'd never start back up once hot.
In the end I figured, hell jump staring it works, so with two batteries it should overcome all the added resistance introuduce from a heat soaked starter. This worked in the end, but then I was on the fence of thinking I took weight off the front but now added another 30-40lbs oif battrey overall in the car. Seems for some they get by with a single battery in the trunk, but if you have real tight header/starter clearance or a high compression/large cube motor, then leaving the battery up front or going to two in the back might be your solution.

-Jason

Thanks for the advise that is what I like about this forum, gear heads sharing expierence, both good and bad. Anyhow I went through the starter, bought a heat shield/wrap and installed it with the freshened up starter which is by the way an SRE gear reduction style, upgraded the ground cable from the battery to disconnect to rear of the cylinder head with double ott cable, it wan't the nice flexible welding cable but still plenty capable 00,I also have a fabed sheet metal shield.Drove to drag strip which takes about 10 minutes, shut it off waited 10 seconds and attempted to restart, I could almost turn it faster by hand, waited 10 minutes and tried again barely got it started and checked the timing, I had previously retarded the timing to help with the no start and it was at about 2ATDC, just for grins I advanced it to 10 BTDC shut it off and it really turned slow, hooked up jumper cables and tried, it turned over well enough to start, but still not good. So drove it back home and hooked up a charger. I plan on getting the battery fully charged and then tomorrow try it again, I will get my father in law to measure amp draw when I engage the starter, the battery has been trunk mounted for years with out this problem, if it still sucks tomorrow I will probably replace the starter, I recently searched the forum and found a thread about using an F250 starter, I thought it said from a 96 460.

My 94 F350 460 was burning starters, starting fine when cool, then seizing when hot, cranked, then hit a stop and wouldn't crank enough to start. I thought it was about the starter getting too hot, as when I would touch the starter, it was red hot. But that was always after the starter seized when the engine was hot. I put on heat shielding, replaced battery, solonoid, replaced two starters, distributor cap, everything new, and the same problem would occur. But then I think I figured it out and I fixed the problem. This latest replacement is giving no issues. Here's what I think is happening: the older flex plate or flywheel gets hot, warps, and then the starter seizes when you try to start it because the starter gear can't ride over the deformation. The warp puts too much pressure on the starter gear and bearing and there is no flexibility in the starter mount to allow for such a deformity. New starters work for a week or so, then do the same thing and then get fried, quiet the mystery. When the engine cools down, the flex plate shrinks back or straightens out and stops seizing the starter. The starter gets very hot when you try to crank the engine and the starter motor seizes with all that amperage going through it. I'm sure that aggravates the issue and accelerates the new starter's demise. The starter seizing, even for a moment, burns up the brushes, so the starter fails quickly. It is the interface between a hot, deformed flex plate and the starter that causes the issue (not the starter getting too hot when you are cruising around). Here's what I did: I added two heavy lock washers to each of the two bolts used to mount the starter. I put locktite on the threads, crank them all the way down, then backed them off about 1.5 turns, maybe two, so it is the spring pressure of the lock washers is holding the starter in place. I added locktite, medium, to the threads, so they won't back out. There is no shim kit for the F350, but the lock washer mount holds the starter in place well enough, yet allows the starter to flex in its mount if it hits a bump in the flywheel. So far, the problem is solved. The starter cranks smoothly. I tried one lock washer and still got some hesitation, but two seems to make it smooth no matter the temperature. Replacing the flex plate or flywheel is probably the better fix, but this is the cheap, quick fix and it works. Hope it helps others with this problem. I read about a lot of frustration about this while I was trying to solve it.