Pull the plugs. See if any are shiny and clean. If your losing coolant, and its intruding through the gasket, you may be able to notice it in the cylinder just by checking the plugs.

if you find a wet plug, chances are high you fou d the leak at that point. Another old school method is to rotate the engine and find TDC for each cylinder. Then using an air hose fitting and compressed air, thread it into the cylinder plug hole. With it at TDC, the valves closed, if you start pushing air into the cylinder, if the gasket is compromised, then you will see air bubbles start to form at the filler neck. I did this before when I didn't have access to a coolant pressure tester and it showed that the gasket was shot on the passenger side if my 302. It ended my headache of blowing coolant out and the water being clear when flushing. Everytime I drove it, coolant would blow out the coolant reservoir tank.

Be sure that if temps are dipping below freezing, add some coolant or your problem will become huge if the block freezes.

Even the head gasket is compromised, don't fret. The 300 isn't that hard to repair. Heavy though, if you end up pulling the head, it needs to be milled for straightness as any 300 head that may have overheated always should be checked.

 

Ok I got the compression test, I couldn't even hold the pressure, so much air was escaping at the top hose where it meets the radiator, I bought a new hose, fingers crossing that's where the air is coming from.

 

Could this be causing the air bubbles at the radiator cap and overheating?

 

No mis info from me Joey......Been a Ford mechanic for MANY years and fixed MANY trucks where they overheat because the owners pulled the t/s then complained of overheating....They can't figure it out either. If coolant circulates too fast and isn't restricted, the radiator can't cool it fast enough it overheats.......JB.

 

interesting ... my 40 years of maintaining/repairing my own vehicles (and a few others) would never have led me to think that this was possible, but i will defer the superior knowledge and experience of someone who does this full-time and say ... "i stand corrected, sir" .

 

Not wanting anyone to "stand corrected" but if you ever have a vehicle that is easy to remove a T-stat, pull it and leave the cap off . Watch how fast the water flows through the radiator. Increase the RPM's and it really cranks it through. At least it was that way in the older cars and trucks. I'm not superior, just something I have encountered many times as people did not like how hot the cars ran when this emission stuff went into effect and they pulled the T-stats. I better be quiet as I am giving away my age!!!!

 

i have no problem with being wrong... it has happened before ...and i am glad to have learned something. it just always seemed more logical to think that the faster the water got away from the combustion area, the cooler it was going to run. but, as i say, if someone with more experience knows otherwise then i accept that info gratefully.

 

The coolant flows too fast through it to absorb the heat and to fast through the rad. to dissipate it. I don't really understand it either..........JB.

 

It's all about pressure, fluid under pressure has a higher boiling point which aids in heat transfer from engine to coolant, that's why if you open the rad cap on a hot engine it erupts everywhere, you suddenly relieved the pressure and the fluid instantly boils.

 

So you're saying with the radiator having the hole, or hopefully only the hose being messed up the air is getting in and thus allowing no pressure and overheating the truck?

 

Air doesn't come in through leaks in a cooling system,the air inside is just the absence of coolant, but let's rule out leaks and t stat first. Your video I'm guessing was you pressure testing the system, if you hear a hissing sound spray soapy water in the area you suspect, it should blow bubbles revealing the leak.

 

Same about psi. If the radiator cap is bad, it'll never build psi and the engine will allows run hot. I had that happen on a '92 S10. Did everything, including water pump, come to find out it was only a $8 radiator cap.

 

When I refer to pressure that's what I mean, psi is the unit in which pressure is measured, and yes, a rad cap that won't hold pressure will cause that problem, you can pressure test the rad cap to verify this.