Running hot- over flow cap blowing off
 

Hey guys. I have an 2002 4.0 SOHC 4x4. It has about 177k miles. I just inherited it from my deceased grandfather. The truck didn't get used much and sat a lot. It's runs relatively well. However, it will occasionally get slightly hot. Not all the way to the H, but about 3/4 then back down. Didn't stay hot Long. Also the heat only works intermittently. According to the paperwork in the console, it's had a new radiator, T-stat and housing. I noticed that the overflow cap has been blowing off and the coolant in the overflow was bubbling aggressively. Any ideas? Blown head gasket? Stuck thermostat? Bad radiator cap?

Yes, reads like a blown head gasket or cracked head but very unusual for a 4.0l SOHC engine, 4.0l OHV did have that issue

There is an easy test for blown head gasket, called the Glove Test

Things you need, latex glove with rubber band or tie strap, OR a balloon, or even a condom
Putty or gum or vacuum cap

Cold engine
Remove radiator cap
Remove overflow hose from radiator cap opening and plug that port with putty, gum or vacuum cap
Put glove over rad cap opening and seal it with rubber band or use the balloon or condom over the cap opening
So cooling system is now sealed tight

Disable coil pack, unplug its 4 wire connector so no spark/no start

Now crank the engine over and watch the Glove
Should just lay there
If it starts to jump up and down then its confirmed, you have a cylinder leak into cooling system

Not that you need to but you can ID which cylinder it is
Remove 1 spark plug and crank engine again, if Glove still jumps up and down then remove next spark plug(you can leave the spark plugs out)
When you remove a spark plug and Glove stops jumping, that's the cylinder with the leak(blown gasket)
Put last spark plug back in, and crank again just to confirm glove bounces

The reason the heat in cab comes and goes is because a cylinder leak pumps AIR into the cooling system, and this causes the overheating but the AIR also blocks the flow of hot coolant thru the heater core in the cab, its called an air dam, which will clear after a bit but will come back as more air is pumped in

The overflowing coolant tank is because the cylinder with the leak is also pumping in PRESSURE to the cooling system, radiator cap is only rated at 16PSI pressure, cylinder has 800psi at least
So that pressure pushes out coolant in to the tank until it overflows or the AIR starts coming out and it bubbles

You should also check the oil to see if coolant got in to oil pan, looks like a milkshake
And white smoke out the tail pipe that smells "sweet" is also a sign of blown head gasket
These often don't happen but is a sign

dang. I'm really hating to hear that my suspicions might be confirmed. I'll do the best when I get some time. Would it be better to repair the engine or just do an engine swap?

Also, I wanna say it was more of a boiling look than bubbling in the radiator overflow

https://cimg8.ibsrv.net/gimg/www.ran...09e4f5a443.jpg

That can be just condensation and a sign you need a new PCV valve and to clean PCV system hoses

Check dip stick

With the 4.0l SOHC you should pull the engine to fix head gasket issue, because of the over head cams and timing chains, but not required

At 177k miles on the bottom end(assuming no coolant in the oil) just redoing the heads would be OK, 400k on the bottom end is normal

A used engine is a roll of the dice, for the 4.0l SOHC it would have to be a 2005 to 2011 engine, and swap over your upper and lower intakes to make 2002 wiring match

In either case you need to change the 2 timing chain tensioners, use motorcraft only
Inspect thermostat housing and replace thermostat
Water pump is your call



Head gaskets do not just "blow" there was a reason, and that was usually overheating it very badly
All metal expands when heated
The head gasket is sandwiched in between the metal head and metal block, and these are held together by bolts torqued to 80+ft/lbs
When an engine is over heated the head metal gets the hottest and it can't expand up because of the bolts, so it expands DOWN........and if it expands down far enough it CRUSHES the head gasket
So not a chicken or egg thing, there was a reason, could be clogged radiator, failing water pump, operator neglect i.e. low coolant level

could it be a bad radiator cap? I know where the PCV valve is. How hard is it to change?

Also, the reservoir doesn't bubble when the engine is cold from what I can tell.

Just do the glove test and find out

Or just take off the rad cap(cold engine)
Make sure radiator is filled to the very top
Start engine
Watch radiator opening
Might get an initial "burp" of coolant coming out, then it should just sit there NO overflowing
Let engine idle for 2 min then shut it off
If no overflowing then head gasket may be OK
If coolant suddenly drops then you had air in the system, add more coolant/water at that time, to the top, while engine is still idling

If it starts to overflow then there is a head gasket issue so no use pursuing other things

just did a coolant flush and refill and put a new rad cap on. Drove for 30 min and temp gage stayed normal. What is the normal operating temp for this engine?
https://cimg3.ibsrv.net/gimg/www.ran...30f538e9bf.jpg

190-195degF

Just below 1/2 on the Ford temp gauge is normal warmed up, 1/2 is about 205degF

After sitting overnight open rad cap and make sure coolant level is at the very top, no air at all in radiator

Here's a video if it running with the cap off

Not looking good

You needed to fill it up to the top while its was running, that up and down can then be seen more clearly, and it does look like a blown head gasket sign
Fluid in the radiator is NOT circulating until thermostat opens, so the fluid in radiator should just sit there, no motion at all
The up and down comes from lower radiator hose, and is caused by "air" entering the cooling system in the head(blown head gasket), that "air" displaces coolant in the head which you see at the top of radiator as the up movement of coolant

If you were to pull the spark plugs you should find one with a super CLEAN tip, thats because its being "steam cleaned" by coolant leaking IN on "intake stroke" of that cylinder
And you should have "some" white smoke at tail pipe

I hate to hear this. I'm not sure why the gasket would've blown. I never let it get too hot. Then again I don't know if it ever ran hot before I got it. I've never seen it smoke. Maybe a little on a cool morning. I can try some stop leak to get a little more time out of it. Then it'll have to sit until I have money to fix it.

There is a product, well a few, that use "liquid glass" to TEMPORARILY block head gasket leaks
Rislone Head Gasket fix is one I have used on a neighbors car, worked for him for 3 or 4 months at a time, lol, he used it a few times draining and refilling with coolant and another can of Rislone, car was a POS commuter, and when its automatic transmission failed it was junked

The "liquid glass" only reacts to HIGH temperatures, like in a cylinder when it fires, 1,000+ degF, it forms a hard seal and for a time seals the leak, when seal break more "liquid glass" is exposed and hardens

"Stop leak", for coolant leaks won't work for head gasket issues, its not strong enough