Hi, new to the forum.

I have a overheating issue with my 94 ranger, I bought it about 8 months ago and didn't have any problems until the weather started warming up. When I'm driving at 65 to 70 it's okay then when I slow down to 35-40 it starts heating up, never gets to the red on the gauge but when I shut it off it's gurgling in the reservoir. My first thought was the fan clutch so I replaced it, didn't fix it. Since then I've done the thermostat and water pump also the radiator cap. I also ran water thru the radiator and it seemed to flow ok. I'm not sure what else it could be besides the radiator, the oil appears to be clean and it doesn't seem to be losing coolant. Any ideas?

Thank you,
E~

 

Welcome to the forum

Bubbling reservoir means there is air in the engine side of the system
It's not "boiling water/coolant", just air coming out of radiator and into the bottom of the over flow tank(reservoir) and bubbling up to the top
But is a big deal as there should be no air at all in the engine side of the system

Cold engine
Remove either hose from the heater core at the firewall
Remove rad cap and refill system until water/coolant comes out the core and hose, ALL the air is now out from behind thermostat
Put hose back on
Rad cap still off
Start the engine and watch the fluid level in radiator
Should just sit there
Let engine idle for 2 minutes or so
If fluid starts to over flow you have a cracked head or bad head gasket, period
Cracked head or bad head gasket will force "air" into the cooling system, displacing coolant and rad overflows

Probably very small breach but it will get bigger


The overflow system works this way
As coolant heats up it expands in Volume, so 1gal of coolant at 70degF becomes 1.5gal at 200degF(exaggerated)
The radiator cap's main valve is rated for 14psi
As the coolant expands it will get to 15psi and push open the main valve allowing hot coolant to flow over to the overflow tank, this is why there is a COLD and HOT line on the tank
This is normal engine operation
When engine is shut off and starts to cool down if any coolant was sent over to the overflow tank then pressure in the system will drop to -1psi, negative pressure, the smaller SECOND VALVE in the center of radiator cap will be sucked open and pull back coolant from the overflow tank, which is why its hose is at the bottom of the tank, so any air will bubble to the top and can not be sucked back in
So the system is self purging of air
Pretty simple system if its working, lol

After driving over 20min and shutting off engine for a few hours so its cooled down, when you open the radiator cap the radiator should be FULL TO THE TOP always if the system is working
Always full to the top NO AIR at all in radiator
If there is air then you have a leak in the engine side or a cracked head or blown head gasket

 

Ok thank you, I will try that and see what I get.

My only question is, if theres air in the system why does it bubble only when hot?

 

Cooling system runs with 14psi internal pressure, air will compress more than a fluid, and air rises to the top of a fluid so will collect at the top of the radiator
As the coolant warms up and expands the air will allow more compression/expansion, like a Degas cooling system, but once it reaches 15psi the rad caps valve is pushed open and the air at the top of the radiator is the first to be sent over to the overflow tank and it bubbles up to the top of the tank

The real question is WHERE is the air coming from
If you remove a heater hose at the firewall and refill system from rad cap opening ALL the air in the engine can escape and be replaced with fluid/coolant
So if all the air is gone then overflow tank shouldn't bubble when rad cap's main valve opens at 15psi, just warmed up coolant should flow to the tank

A cylinder has 150psi cranking compression, and 1,000+ psi when it fires, that's what pushes the piston down to turn crank shaft
If there is a cracked head or blown head gasket some that pressure will go into the cooling system, and its "air"(exhaust gases)
This does two things, the "air" displaces coolant in the heads, causing them to run hotter, and the higher pressure forces the rad cap to open sooner
So the overheating is from "air" in the cooling system

So the question should be where is the "air" in the cooling system coming from
As said the overflow system is self purging of air after one warm up and cool down, so there should be no air at all in the radiator when you remove the cap after engine has cooled down, 0, none, el zippo, lol


Degas cooling system is what was used prior to overflow systems
If you are old enough to remember metal radiators and the rad caps with the flip up handle, those were Degas systems
Radiators had a FILL LINE on the outside, which left about 2-3" of air inside radiator
Rad cap had a rating of 18psi usually, and had the lever to release pressure and a hose down to the ground if pressure exceeded 18psi or you lifted the lever to expel hot coolant down to the ground
The air at the top of radiator allowed the coolant to expand in volume as it was heated, in air in the system would circulate thru and eventually be trapped at the top of the radiator

2002 Ranger 2.3l Duratec uses a Degas system

I think the overflow system is better because you can add coolant to the overflow tank when engine is overheated and it will be sucked back into the engine as it cools down
Removing a rad cap on a overheated engine is NOT a good idea to add more coolant

 

So I unhooked the line at the heater and did the test, the level in the radiator does rise. Pretty slowly but definitely there, the guy I bought the truck from said he had done one head gasket but I'm not sure which also don't know if he had the head checked for cracks. I'm assuming it would be best to get new heads and do both?

Thanks

 

Did you see bubbles in the rad cap opening while engine was running?
If so you can "sniff" the opening, if it smells like "exhaust" then for sure there is a cylinder leak

Call local machine shops and ask how much, to pressure test and surface each head, and approx. how long it takes once you drop off the heads
Usually takes 2 to 4 days depending on how busy the shop is

The benefit of new or rebuilt heads is time, you can remove old heads and install new/rebuilt heads over a weekend
But you pay more

 

I didn't actually see bubbles, the water just rose up and started overflowing a little. I will try sniffing it when I get off work

 

After 2 minutes water will start to rises up as it expands when heated, but not before

 

I'll time it this time, seemed like less than 2 though