I have a 1996 F150 XLT 200k+ miles, bought it used about two months ago. Ran great when I bought it. Some of the guages were shot when I got her but no big deal (untill she starts overheating and I have no temp indicator). A couple of weeks after I bought the truck the radiater sprung a leak, after a day or two I replaced the oem radiator with a new super cooling radiator from Hi/Lo. The truck gave no problems after a radiator change. Still no time or money to fix gauge. About two weeks ago drove a lot to help move some furniture, when I got back home she was boiling over, thought no big deal because I was hauling a** to get home. I check the coolant befor leaving again and top her off. No problems that evening. The following day I do an oil change and change the oil pressure sending unit. I check all fluids and all is good.

So I Thought, since then my truck has been boiling over any time I drive for more that 20-30 minutes at 50 or above. I changed the thermostat & cap, and my luck the new thermostat was defective. It continued to get hot and boil over. A day or so later I changed the thermostat (this time I checked it before installing it. However even after that the truck still seems to get hot and does boil over. So I changed the lower radiator hose, fan clutch, & water pump. Yet still the truck seems to overheat.

I did through the process get my temature guage to respond, but I am not sure if I can trust its readings. At idle it will mark half way for a while the get hotter and suddenly die (peg past the cold indicator). I have replaced the original temp. sending unit with a new one. I have doone all that a general home mechanic can do.

When I replaced the water pump I also installed a Prestone Flush Kit, follwer the instructions exactly. When I attempted to burp (purge) the cooling system it did well for the first half (no bubbles of air) then after about 20 minutes at idle with the cap off i see bubbles rather big clean bubbles one or two every half a minute or so. Another ten minutes like this then I start seeing little bubles and a bunch of them, all the while I am topping the system off to make sure I can see the bubbles and to not let more air enter the system. So its about thirty minutes into idling the truck with the heater on full blast and the cap off and I start seeing foam form.

Someone tell me what the deal is?
I had the guys at midas look at it, there is no oil mixing with water. no leaking other than boil over which has calmed down a bit but still does on occasion.

I don't know if its related but i do notice drops of water form at the exit of the exhaust.

Please let me know what's wrong with my truck

EPDC

 

If you have a Autozone near you, they have a radiator pressure tester you can borrow/use for free.

You install the test cap and use a pump to pressurize the system to around 16 psi. The pressure should be stable. If it bleeds off, you have a leak some where. Could be a bad hose, bad head gasket, heater core cracked cylinder head etc...

 

How definative is a pressure test? Ihave heard a blown head gasket is sometimes hard to find because of expansion and contraction due to the heat of driving?

EPDC

 

Well since you say the coolant is going into the overflow, that indicates the radiator cap is openining because of the high pressure in the cooling system and you really are over heating. The radiator cap test will find most leaks but is not full proof.

Another method if you have an air compressor is to remove the spark plugs and with both valves in the cylinder closed, slowly put 100 psi into the cylinder, if you have a head gasket leak or cracked head you should see bubbles in the coolant.

Have you looked at each plug? If coolant is getting into the cylinder the plug will have a darker ash color. It does sound like you have a very small leak so it could take some time to find it.