Hey guys im trying to figure out my overheating/underheating issue with my truck. I replaced the radiator cap and thermostat twice. What happens is the engine temp will stay cold for too long, then all the sudden it will skyrocket and overheat and blow coolant out the resevior. It will do this every 1 out of 3 times that i drive the truck. It almost acts as if there is an air pocket that keeps getting in or something. Then again it really seems like a thermostat issue but i have replaced it twice already. Yes i put it in the right way.
The weird thing is if it was a bad headgasket or cracked head, wouldnt it run rough? My truck runs smooth.
Any ideas!!?!?
I need help im getting sick of this crap, i though the 3.0L were supposed to be good motors.

 

It could, might be a small leak? Plus it will only blow out of the reservoir when the T-Stat opens.

You could have your truck pressure tested.

 

I'd recommend taking it to a reputable shop and having them check the cooling system for leaks or exhaust getting into the cooling system.

 

take it to a shop that can test for leaks, pressure, etc..

 

That don't sound like a blown head gasket. A blown head gasket is usually the same all the time.

That is kind of a puzzle. Maybe you need to take it to a radiator shop and have them test it and see what they think.

 

okay sounds like a plan to me. It must be a small leak because it doesnt leak anything, and the oil does not have antifreeze in it. Also, when i take the thermostat out of it, it never has those problems. One more thing, after i get done driving the truck and shut it off, there are bubbles coming up and bubbling in the resevior.

 

I bet the water pumps on it's last leg!

 

I think you have a very small compression leak into the cooling system. I had something similar happen in my race car. It would leak very little coolant into the cylinder but the compression and firing in the cylinder would slowly pump gasses in to the cooling system until the pressure got high enough to blow out the radiator cap. Then it would begin overheating. The problem was a very small crack in the cylinder wall.

I had a similar thing happen to my 428 CJ engine and it would have bubbles coming out of the coolant reservoir after shutting it off. The problem with it was a very small compression leak around a cylinder sleeve. I was able to seal it with an expensive block seal.

It doesn't seem likely that a bad head gasket would have this kind of symtom but it is possble. It is more likely a metal crack.

Both of those vehicles ran very well while it had these symptoms. The compression leak was small enough that the compression was not reduced much.

 

yea it is very puzzling to me! I doesnt run like it has a blown head gasket. Could one of the cylinder heads be warped or cracked just a little bit?
The only thing we could come up with is somehow there is exhaust being pumped into the cooling system.
4LO 4.0- Why do you say the water pump is on its way out?
The truck never overheats or anything else with the thermostat out of it.

I also have tried some headgasket repair stuff that you pour into the radiator with water and it is supposed to seal up everything, and that didnt work either.

 

I had the same problems, would run fine then all of the sudden it would over heat and when you shut it off it would gurgle.
Replaced the t-stat, hoses,clutch fan, even the rad only to still have it happen agian, replaced the water pump and it has never happened again.

 

mine did the same thing. Ended up being 2 cracked heads. It'll get worse before it gets better.

 

Thanks for all of the help guys. Im going to be betting on a cracked head or two. Im dropping it off at a buddies shop today because i dont have any time right now to try and fix it. So when the word comes through, ill let you guys know what it is that causes the weird overheating isssues.

 

Blown head gasket after changing it truck as a massive amount of white smoke and still runs hot what do I do I replaced the radiator,thermostat,head gasket ran motor flush through it changed oil and filter 2 times its a 99 ranger 2.5liter engine 5speed manual trans rwd has 211,656 on the dash what do I do or what am I doing wrong

 

Was there ever a definitive answer on what could be happening? My 91 Ford Ranger's clutch blew out one day last fall
and I had to leave it and come back with a bigger truck and car dolley. While trying to get the truck on the dolly it started
puking coolant everywhere down the front of the engine. I immediately thought water pump but a it was that the intake
gasket had blown right where its meets the head on the left header facing the engine. I ended up going in my self a
and replacing the gaskets but soon after completion I Drove my Ranger around and its startled bubbling out the
reservoir and over heat, but I noticed that when it doesn't bubble out or over heat the temp gauge stays at N on Normal
whereas before it right about the "R" or rather in the middle. I replace the radiator cap, then the thermostat and it didn't
change it. going into the winter it happen less frequently to where I didn't seem like I was a need to fix however as it has
started to warm up again it has overheated several times and mostly does it while idle.
I am about to go in and change the waterpump as the thermostat I replaced was not in the best of shape.
but if it might me a head issue I guess I should see about pulling the heads...

 

Welcome to the forum

Assuming V6 engine, 3.0l or 4.0l?

Probably 4.0l since intake gasket coolant leak was a common issue at that location, aluminum intake and cast iron head caused the gasket to get eaten away, electrolysis because of the different metals and flowing coolant.

But your head gasket IS blown or a head IS cracked.
You need to do a simple FREE test

Glove test
Cold engine
Remove rad cap
Remove overflow hose from rad, plug that rad port,use putty, gum, vacuum cap, ???

Place latex glove over rad cap opening, seal it with a rubber band.
You can also use a balloon or even a condom in place of the glove

Unplug Coil Packs 4 wire connector, you want a NO START

Crank the engine and watch the glove
If it starts to bounce then you DO have a cylinder leak, 100% accurate

If it just lays there then you DO NOT, 100% accurate

If it bounces then start removing 1 spark plug at a time, and crank engine
If glove still bounces remove next spark plug
Keep removing spark plugs until glove stops bouncing, last spark plug removed was from cylinder with blown gasket or crack in the head


Cooling system runs at about 15psi pressure after engine is fully warmed up, this pressure comes from the coolant getting warm and then expanding in volume, so there is no pressure in a cold system, takes 5 to 10 minutes of driving to start getting pressure.

Each cylinder in the engine has 150psi pressure just cranking(compression), when running it's above 1,000psi when it fires.
So any leak from a cylinder to cooling system will push some of that HIGH pressure in to cooling system, and that pressure is AIR.
When that happens the 15psi rad cap is pushed open and coolant flows to Overflow tank, then AIR from that cylinder makes yto top of rad and now overflow tank starts to bubble

The Glove bounces as this cylinder's leaking pressure comes in, when cylinder is on it's INTAKE STROKE it will suck some pressure back in from cooling system, usually coolant, and this will often make for whitish exhaust from tail pipe, if engine is running.

 

It is a 4.0.
I will try the glove test in when I get home from work. I work nights so in about 4 hours.
Thank you for responding back so quick.

I was and am dreading the whole head gasket needing to
be replaced. I can do it myself I have watched hundreds of videos to learn how to
replace the head gaskets in the event the time comes.
Is there a certain brand of head gasket that is preferred, in the event
it does need to be replaced?

 

Kind of commandeered this thread post, sorry haha but it is kind of similar to the same issue.

is there an amount of time you need to crank the engine before determining the glove just isn't bobbing ?
just tried it twice, and the Glove didn't move but I also read that it the coolant/water only bubbles after the engine has warmed up and the crack Or gasket failure opens up. Should I try it with a warmer engine?

I put the glove on top after unplugging the 4 pin wire for the (the name is escaping me at this time but essentially the electronic distributor) and I blocked the reservoir hose by disconnecting from the radiator and putting another rubber glove tightly against it and added another rubber band to tighten around it. Cranked it and no air or glove bob.

wait you said 15psi radiator cap, my 91 Ford Ranger maybe not stock but originally when I bought it had a 13psi cap and was told at Oreillys when I bought a new radiator cap thinking the old failed is also a 13psi cap, Do I have the wrong radiator cap and have just not notice it this whole time ?

 

If glove didn't bounce then no head gasket or cracked head........for sure

Next thing I would do is to by-pass the heater core.
1991 4.0l uses the heater core as the water pump by-pass, if core starts to get plugged up then coolant temp will go up and down after warm up.
You can get a coupler of the right size and just remove hoses from firewall and connect them together or take one hose and run it to the others engine connection.
There is no IN/OUT on a heater core, just FYI.

Test it for a few days with core by-passed, if overheating issue is gone then replace heater core, not an expensive part.

Heater core on 1991 is easily replaced if it is the problem, 4 screws on a bottom plate under the glove box.
Put a towel down under core area
You need to tilt core back to clear firewall then tip it again to wiggle it down and out
It does have some weather stripping around the core for better air seal, and you can add new weather stripping to new core, or not, up to you.

 

 

Pressure Leak between cylinders will cause misfires, for sure, but can't cause over heating, if anything the engine would run cooler, misfire means 0 heat from that cylinder

You need a connection to the coolant passages that surround each cylinder for a gasket or crack to cause overheating.
4.0l OHV heads did have a casting issue between valve seats in the head, metal was too thin, if over heated, head metal expands and can crank where it is thin, between valve seats.

If you didn't have the heads checked, pressure test, and overheating was why you changed the head gaskets then I would suspect you had a cracked head and didn't see it

The Glove Test is a Free pressure test