Overheating when driving and gas tank building up pressure

[Adam1966C10]

Almost done with my 66. I've taken it on a few test drives and it starts to overheat when on the highway (got up to 230) and it isn't even hot here in Texas yet. It will sit at idle and the electric fan will cycle just fine. I have a newly rebuilt 350, new aluminum 2 row radiator with a single fan mounted on an aluminum fan shroud from Brothers Trucks. I have the Fitech efi with the fuel command center. The timing has been double checked so it is not that.

The other thing that is happening I'd the under bed fuel tank some how becomes pressurized. It starts to bow out on the top and bottom. I have a tanks Inc vent on it and can see capers coming out of it, but it can't keep up. I have to remove the gas cap to release the pressure. The fuel command center has a return line. I pulled it and is doesn't seem to have enough pressure to pump up the tank.

Any advice would be much appreciated.

[The Rocknrod]

What temp gauge are you using and where did you get the sender?

[Adam1966C10]

Actually I have two. One is in the intake manifold and it came with the Fitech system. I was using the display to watch the temp. The second one is in the drivers side heat and goes to the dash. No numbers but goes all the to the red line.

[blown240]

Are your fans ON all the time? Or are you having your Fitech control them?

Fans on all the time can cause overheating on the freeway...

[Adam1966C10]

The Fitech is controlling it, I don't think it turns it off, but I could be wrong.

[The Rocknrod]

The gage (assuming it's a 66) will read high if it doesn't have the correct sender.
https://www.lectriclimited.com/elect...ing-unit-87590
Also see: http://67-72chevytrucks.com/vboard/s...d.php?t=525139

[Adam1966C10]

That's what I thought, but the Fitech digital read out was also indicating that is was at 230, I don't think bouth would be reading wrong.

[padresag]

depending on what pressure cap you have and coolant mixture you can run at 230 without a problem.
If it is getting hotter on the highway it could mean an air flow problem and sometimes it can mean a bottom rad hoce collapsing. is the bottom hose a wire reinforced hose or just rubber.
ron

[padresag]

but 230F is not really a problem as I mentioned. what pressure cap and coolant mixture are you using? I also don't know what a Fitech is.
ron

[Adam1966C10]

This is Fitech efi system I have.
http://fitechefi.com/products/30003/

Not sure about the cap, it came with the aluminum radiator from Brothers. I remember that it says champion on the cap. I believe it's just a 50/50 coolant mix. I'll have to check the lower house, but I think I remember the spring being in it.

Could it be the fan not letting the air flow properly at highway speeds?

[padresag]

water boils at 212 degrees F normally at sea level without any pressure. they more than likely supplied you rad with at least a 13# cap and you have a 50-50 mix. for every # lb pressure that you add to the system you will raise the boiling point 3 degrees F. a 13# cap will raise the boiling point 39 degrees. a 50/50 will raise the boiling point another 18 degrees F, add 212 + 39 +18 =269 Degrees, your system will not reach boiling point until 269 degrees. 230 is not a problem. this is why they installed idiot lights in vehicles instead of temp guages.
ron

[padresag]

re your fuel tank you are having a venting problem somehow. when gas gets hot it expands. if you system is drawing fuel from the tank and it is not vented the fuel being drawn causes a vacuum and can cause the reverse action; causing the tank to indent. with your injection it must have a return line. you say that there is a vent on the tank; are you sure that it is working. is your gas cap vented, if not I would try a vented cap
ron

[Adam1966C10]

I'm using this vent.
http://www.tanksinc.com/index.cfm/pa...prod/prd98.htm

I can see the vapors coming out of it. I have an under bed tank with a pop up cap. I looked and couldn't find one that was vented.

[Adam1966C10]

By the way thank you for your input guys.

[padresag]

if you had of installed a 3 or 4 core rad it more than likely would have run cooler as you are running a greater volume of water. the main reason for raising the pressure of radiators was due to the use of smaller rads and smaller openings in the grille areas years ago.
ron

[Port&PolishMan]

Originally Posted by padresag

if you had of installed a 3 or 4 core rad it more than likely would have run cooler as you are running a greater volume of water. the main reason for raising the pressure of radiators was due to the use of smaller rads and smaller openings in the grille areas years ago.
ron

I haven't read all the way through , but My 350 has a Desert Rated Rad in it and
I'm still up at 210-215 then it goes back down to 185 and Up again in Traffic

I'm putting in a Precision Stat , those Respond Faster and Hold Temps more Evenly .

4 Row for Sure , in Texas - Dam Hot there .
Also I - like to Note - with 2 Core - Your Pushing Water through it to Fast .
I'm sure You could - Tweak it - By going to Under Drive Pulley's ,180 Precision Stat , & Pusher Fan ..

[padresag]

Believe that it was 63 or 64 that they raised the pressure in the cooling system of these trucks from a 7# to a 14# pressure system and a 16# pressure with a/c. so there had to be reasons for that
ron

[shp4man]

Don't know if it will help, because my truck is a stock six cylinder with the Harrison radiator still in there. Anyway, it would have some wild temp fluctuations and get hot on the freeway. It had a 160 degree thermostat in it.
Looking at parts catalogs, GM recommended a 195. I was skeptical, but put in a decent quality 195, and it seems to be fixed.

[lumpy63]

If I understand correctly your truck will sit and idle without overheating? But on the freeway it runs too hot? The cooling fan basically becomes useless over 30 mph as the incoming air overtakes the fan. This could be a case of insufficient cooling system capacity ,or miss matched parts..I have seen people put serpentine counter rotating water pumps on standard rotation sbc's double check your cooling system.

[urmyboyblue]

1. Is the fan pulling air thru the radiator? It needs to based on how it is mounted- if it pushes from the rear, it will lose efficiency at speed due to the incoming air from the front being pushed by the fan.
2. Does the FITech show you AFR? If so, what is it showing at cruise?
3. What fuel pressure are you running at?

Do a little research- I read that the fuel command systems were causing issues for some people.

[61K10]

you have a flat piece of metal covering the rad with just a hole for the e-fan. with the fan on at speed, it actually blocks the air through the rad. try turning the fan off, and see if any difference. As Lumpy63 say's, could be something else.

[Adam1966C10]

I'm beginning to think I have a combination of problems with regards to the overheating. I read this
http://www.tanksinc.com/index.cfm/pa...ode=prod/prd98.
I called Brothers where I bought the radiator from to see I'd they had any specs on the row size, they did not. So it is possible that it is undersized. I do have a solid piece of aluminum used as the shroud with only a hole for the fan which is on the engine side of the radiator. I'm pretty sure the fan does not turn off at speed. It is controlled by the Fitech system (it doesn't monitor speed) and the A/C switch.

I found this link about the Fitech fuel command center.
http://fitechefi.com/tech-posts/go-e...with-pictures/
I'm going to try this adjustment and see if it helps the build up of pressure. Some people were having fuel come out of the return line, but I just have vapor coming out of mine. I have a tanks Inc vent installed on the fuel tank under ther bed. I added a "T" to the return line just before it enters the tank. Is it possible that I am getting a vapor lock since the warm gas vapor coming from the engine is blocking the vent? Should I have the vent on a separate line?

Once again, thanks for all the feedback, I really appreciate it.

[padresag]

http://www.tanksinc.com/index.cfm?pt...id=-1&mode=cat
ron

[Adam1966C10]

That is the way I have it mounted. There is a "T" right in the return line before the inlet nipple. Is it possible that having it in the return line before the tank is not letting the vent work properly?

[padresag]

Originally Posted by Adam1966C10

That is the way I have it mounted. There is a "T" right in the return line before the inlet nipple. Is it possible that having it in the return line before the tank is not letting the vent work properly?

should be in the tank as that is what you are venting. when your vehicle is running that line is returning to your tank. if there is product in the line, it will not vent against the incoming fuel. it will vent after you shut the engine off as fuel will not in the line.
your vent hose should steadily rise also and not have a dip in it as it has in the illustration
ron