Coolant Loss

[NPdarkside21]

I noticed coolant escaping through my radiator cap recently. I was told it could be my head gasket or a bad radiator cap. It has 214k miles and the last engine overhaul was done at around 195k miles which included a complete gasket exchange, head resurfacing, and tune up. Since then, I have replaced the water pump and both upper and lower radiator hoses and the cap. Oil is not turning milky and no smoke out of the tail pipe. Should I just change the cap and radiator or is this a head gasket issue?

 

[Rearanger]

Cap first - it's cheap.

Usually if head gasket there'll be transfer of coolant to oil or cylinder or from oil to coolant. A head crack can show up as boiling coolant into coolant reservoir and overfill of reservoir when hot.

 

[RonD]

Coolant is suppose to leave the radiator and go to the Overflow tank, it does this thru one of the two valves in the radiator cap.

Coolant like all liquids(and solids) expands in volume when heated
So as a cold engine heats up the coolant expands in volume, this causes an increase in pressure in the engine and radiator.
Radiator cap has a larger spring and valve set for a certain pressure, say it is set for 14psi pressure, at 15psi spring is pushed up and warm coolant flows out thru overflow hose and into the overflow tank, and it flows until pressure is under 14psi then spring closes valve.

This happens every time engine is warmed up to operating temp, if you look at the side of overflow tank there will be a COLD and WARM line, marking the expected coolant levels in the tank at those engine temps

After the engine is shut off it starts to cool down.
As the coolant cools it shrinks in volume and pressure in the system starts to drop, when the pressure gets to -1psi the smaller center valve in the rad cap is pulled open, and sucks coolant back in thru the overflow hose from the overflow tank.

The overflow hose and tank are an important part of the cooling system.
Hose must air tight/leak free
Tank must be clean, free of debris that could block the flow of coolant back to rad as engine cools down.

When you remove rad cap on a cold engine coolant should be full to the top, no air
If not then overflow system or rad cap could be bad
Or engine side of system has a leak, but you should see that as puddles on the ground

Pressure in the cooling system only starts to increase as coolant gets warm, above 150degF, so takes a few minutes of running time

So when engine is cold remove rad cap
Start engine
There may be a "burp" of coolant from rad cap as water pump displaces some coolant, but then coolant level will remain stable.
If coolant continues to flow out of rad cap opening then you do have a cylinder leak into cooling system, i.e. head gasket or cracked head issue

You can also do the free Glove Test(search site) it can confirm cylinder leak and also tell you which cylinder is leaking.


Newer head gasket material is much better than past material, so a blown head gasket can cause coolant to flow into an oil passage giving you overfull dipstick and milkshake color, but it doesn't happen as often now
"Blown" part of a head gasket is the soft metal ring that seals between head and cylinder, when it fails pressure inside the cylinder, 900+psi, pushes out past the ring into the gasket material, since a cylinder is surrounded by coolant passages, it will usually breach one of those passages, and some of that 900+psi pressure is pushed into cooling system causing instant rise in pressure as soon as engine starts.
This pressure is "air"(exhaust), and this air is now in the head's cooling passages, air doesn't cool as well as a liquid so engine will start to overheat.
As water pump circulates coolant the air will circulate with it, and being air it will stay at higher areas, so can often be seen as bubbles at rad cap opening.

 

[NPdarkside21]

Update "Leaking coolant"

I replaced the cap and it still leaks coolant out of the cap. No coolant in oil and no oil in coolant. Most of the coolant I've put in to refill goes straight into the overfill reservoir or out the cap. Engine has lost power since but no difference in idle, fluid and no check engine light (yet). Found out this is the original engine with 214K+ miles so it's pretty old.

Would it be better to replace the heads?
-or-
Would it be better to replace the whole engine?
P.S. I also have a rear main seal leak.

 

[Rearanger]

I replaced the cap and it still leaks coolant out of the cap.

The coolant should be going to the reservoir, not out the cap and down the rad, unless the overflow tube to the reservoir is blocked. The reservoir has it's own overflow. Have you done a cooling system pressure test?

Engine has lost power since but no difference in idle, fluid and no check engine light (yet). Found out this is the original engine with 214K+ miles so it's pretty old.

I'd suggest a compression test. Personally, if the engine has been looked after then 214k is not that old, but not sure how Ford built these engines. Has there ever been leak sealant used in the cooling system?

[quoteWould it be better to replace the heads?
-or-
Would it be better to replace the whole engine?
P.S. I also have a rear main seal leak.[/QUOTE]

I think you have to try and find the problem before making those decisions.

 

[fr7]

I had that problem before but mine was solved with a new radiator cap. Did you check the small hose that goes from the radiator, right next to the cap, to the coolant reservoir to make sure it's not plugged? When coolant heats up it builds pressure, that pressure needs to go somewhere. When I checked mine it was completely clogged, I pulled it off and blew it with an air compressor to open it. You can also check really carefully around the cap just to make sure you don't have cracks or dents. Just a thought, you can give it a try and see if it helps.

 

[jim22]

On my truck, the overflow hose connection under the cap was leaking. I solved it with a little blue rtf sealant and a small hose clamp.
Jim