not overheating overheating problem

[icalbert101]

yeah I'm confused too. in the morning when it's cool out I can drive and drive and drive and everything functions as normal. by the end of the day when I drive home the thermostat will not go above half it stays at normal operating temperture. BUT when I shut the truck off the water boils out of the camp. now it did this with the stock radiator and I've since upgraded to a griffin and it still does it. I have tried re routing the overflow line and it had no effect. the overflow line is clear I can blow through it just fine. if I take the rad cap off while it's running it doesn't boil over like a low compression motor would. I'm just tapped out of ideas. any suggestions would be greatly appreciated.

 

[Rearanger]

New rad cap?

 

[adsm08]

Sounds like a bad cap to me too.

 

[RonD]

Yes, rad cap

And check that overflow line for a leak, it might be clear which is good, but a small crack will cause the system to pull in some air when cooling.
Once there is air in the system you will get the symptoms you have.

The overflow/expansion system only works if it's full of coolant with no air leaks.
As the engine warms up coolant should expand, this pressurizes the system to appox. 16psi(rad cap rating), once above 16psi the larger valve in the rad cap opens and allows coolant to flow into the bottom of the overflow tank.
The bottom being the key word, so overflow hose is always covered by the coolant that's already in the tank, any air in the rad would be pushed out first and bubble up into the overflow tank, so system is self purging.

When engine cools down the coolant volume shrinks, when cooling system gets to -1psi(relative) the smaller valve in the rad cap opens and pulls coolant from the overflow tank back into the rad.
If there is a leak in the overflow hose air and coolant will be pulled back in, most of the air would be purged at next startup but some might get into the system.
Air in the cooling system can turn to steam when circulation stops, i.e. engine is turned off.
So you get a quick boil over.

Ford Rangers used overflow tanks with overflow hose fittings at the bottom, which saves money but can also cause issues.
Debris in the cooling system can happen, and some will get pushed out into the overflow tank, it will settle at the bottom and can block return flow.
So tank should be cleaned or checked as part of regular maintenance.

The other type of overflow tank design has the overflow hose going to the overflow tank's cap, and then another hose on the cap that extends almost to the bottom of the tank, this allows any debris to settle to the bottom and keeps the return open.

 

[icalbert101]

the latter example is how we modified the current coolant reservoir to operate for trouble shooting purposes. I'm going to guess it's the line going to the reservoir because the Cap is a brand new griffin to match the radiator this same problem existed before the radiator swap though too the radiator made it no better now worse

 

[RonD]

Yes, if cap is good then most likely cause is air in the system.

When engine is cold I would pop off the cap and make sure coolant is all topped up.
Then I would put a piece of tape on the overflow and mark the coolant level for Cold, and then after driving a bit mark it for Hot.

If coolant is below cold mark the next morning then you have a leak.
If coolant is above the cold mark then system is sucking in air instead of coolant when it cools down.

 

[adsm08]

After cooling system service the best way to make sure you get all the air out of the system is to fill it at the heater hose and not the radiator. If you fill at the radiator the air gets pushed to the top of the system and gets trapped.

If you pop a hose off the heater core and pour coolant in there you have opened the system at the highest point and as you pour coolant in one end it pushes all the air out the other. When coolant comes out the heater core you have all but the smallest bubble out.

Try that if you think you have an air pocket.