My truck (1980 f350 400 2bbl) has been giving me problems.

Originally the truck would overheat and vapor lock. (some say the 2 are unrelated but I am getting both)

Recently I have had a big problem with vapor lock which a few times I killed the battery trying to start it. The other day I turned the truck off and when I tried to start it the battery was dead- odd. I'm pretty sure I don't have any bad grounds but I'll check again. I've checked this battery a number of times and it's always good.

The reason for this post however is a possible concern with the Head Gasket. When I check the oil and transmission fluid they look flawless, however, today I got under the truck and saw this:


That lovely oil/antifreeze gray. It's on the oil cover back to the transmission cover. What I find odd is that the dipsticks are pristine. This used to look like there was a little oil transmission fluid on it.
Before I saw this, I talked to the head mechanic at work and he was thinking that the Head Gasket might be blown on the "exhaust side". I told him there seemed to be too much moisture even with the cold (and just a little smoke), and that it has a hard time accelerating. I can get up to speed slowly, but if I have to tap the brakes, it takes a minute to get back up. The truck doesn't feel like it wants to even go over 55mph. I just flushed the radiator and block, so is it possible that this was runoff from that?

Again:
the fluids are clean
there is only a little "smoke" when I start the truck, but it's cold outside
there may be excess condensation in the exhaust
Gray gunk on the bottom of the truck
I don't see or feel the heater core leaking inside or out.



I have changed:
Carb
distributor
alternator (switched to chevy alt)
fuel lines (except the metal one from tank to pump)
3-4 pumps
fuel filters
2 gas caps
Valve cover gaskets
Vacuum lines
Dropped down to 1 battery
Main power ground wire

And more I can't think of.

Thanks.

 

Just pull the sparkplugs. If you are burning antifreeze, you will see it on one or more of the sparkplugs. If it really gets bad, the anti-freeze will short out the plug and the engine will miss-fire.

 

I think thats what you're seeing, Is the truck still overheating or just vaporlocking?

 

I pulled the plugs but didn't try to start it ( I was reading around last night and it seemed some want you to remove all but one plug or remove one at a time?). The ones I checked were dry except a little oil.

It hasn't overheated yet but it only seems to if it sits in one spot. I dropped to a 180* Thermostat (195* normal I believe). The needle points barely to the right of the far left marker for normal range when driving. The other day it did get up to the middle of the normal range while idle. Hasn't overheated since it was 70's but it did vapor lock last week. It has also been idling hard.

For the vapor lock I'm starting to think it might be the gas tank. I've never cleaned it and I'm afraid that there might be some junk in it from the previous owner that is killing the pumps. I installed a filter before the pump last time I changed it, but I'm thinking the line might be clogged or debris is getting by the filter and killing the diaphragm. My brother suggested I put an electric pump on and I'm leaning that way, but I still want to clean it. I checked the fuel lines by hand and they definitely weren't hot or even warm- even the carb was "cool"

The overheating part I'm still lost on.

 

This happens all the time so don't feel bad, but you are spending a lot of time and money on a factory gauge that is just about as worthless as they come, and does not tell you anything about the actual temperature the engine is running.

 

The vapor lock is the real concern. I bought a fan clutch but found I need to replace the fan too(ran out of money on that venture before purchasing the fan) . I Have a flex fan on there and love it or hate it, I don't want one of the fins flying off while I'm driving or under the hood.

 

You didn't list any troubleshooting you did leading you to the conclusion it truly is vapor lock.

Are you definitely running out of fuel? How do you know?

 

I have a clear filter at the carb, when it locks there is no fuel in it- Dry.
I have to wait until I see a little in it before I can start the truck again. Last summer it died while idling and I pulled the top off the carb and sure enough there was no fuel in the float bowl.

I've had this problem since I got the truck 3(?) years ago but I wasn't able to diagnose it the first year or so.

 

I would check the relationship of the fuel line to the exhaust system. If either one has been changed, it can be the cause of your problem. Engine overheating will not cause the fuel filter to run dry, since that side is pressurized. The suction side of the pump is the area prone to vapor locking.

The factory had a single exhaust system on the passenger side, and the fuel line runs on the driver's side. Has anything been changed in this area?

I had this exact same problem on a 53 f100 project. I had put a 351c with headers in place of the original six, but used the original fuel line system. I also had a fuel filter that would run dry when I was in town idling. I had to take and run the hard fuel line on the outside of the driver's side frame rail to avoid the dual exhaust, and then shoot through the frame straight to the fuel pump at the engine. This solved the problem on that truck.

 

That sounds like what my truck has. The gas tank goes over to the driver's side frame, then there is a metal fuel line that goes from there to the front. At the front it has a rubber fuel line that I put a metal filter on before the pump, then another rubber line to the pump, then I replaced the metal line from the pump to the carb with a rubber one on a brass elbow and put another larger rubber line over it as a protective sheath. The fuel line is nowhere near the dual exhuast.

All these changes were done to correct the problem to no avail. I changed all the lines/filters except the metal one along the frame. The only other thing I haven't changed is the gas tank itself and the "pickup tube(?)" and sending unit.

 

As a quick test, get something to wrap around that metal filter. That filter doesn't need to be there, the stock system has a sock where it picks up fuel inside the tank(but you do need a filter like that before it enters the carb). You might think about taking that pre-filter out.

If you have headers, that is going to increase the heat radiated on the front frame rail. If you could also stick something over that part of the line to shield it from heat radiated from the exhaust, you could see if that helped.

On that old 53, my headers where at least 3 or 4 inches away from the fuel line, but the radiated heat caused it to vapor lock. I would not vapor lock driving down the road, I guess there was enough air flowing by to keep it cool. But sitting around idling is when the problem came up.

If you had something that you could temporarily put around the line, you could quickly determine if that was the problem or not.