Topping off coolant

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Greg Gibbs

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I have a 2002 4x2 Sport Trac with 153K miles. Recently, I decided to do some preventive maintenance and install a new fan clutch, water pump, radiator hoses, bypass hose, and heater hose. Obviously, this required draining the coolant from the radiator. When it was time to refill with coolant, I filled the radiator up with 50/50 mix, turned on the heater to full heat with the fan on low and then cranked the engine to let it warm up. The coolant level in the radiator dropped a little as air was pushed through the system, but then the coolant level began to rise until it was overflowing for a while. (This was unexpected and I don't know what would cause that to happen.) Once it stopped, I put the cap on. I also added a small amount to the reservoir, but it was near the fill line.

The next day, I checked the coolant level in the radiator after driving it and letting it cool down. It was not full, so I added a little more coolant to the radiator. Same thing happened today. The level in the reservoir appears unchanged. The truck is not overheating and I don't have any obvious leaks. The heater works well, so there is no air lock. The thermostat housing was replaced about a year ago, so I don't think that is an issue either.

Do I just have air in the system? If so, how do I get it out? Should I just keep adding coolant until it stays full?

Any ideas why the coolant level rose and overflowed with the cap off?

Why hasn't the coolant in the reservoir been pulled into the radiator?

Thanks for any help you guys can offer!
 

Todd Z

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The level rose as the coolant expanded while it was getting hot...... BEST way is check the radiator when the truck is COLD first thing in the morning and keep the reservoir at its proper level. IF the radiator cap is working properly it will adjust as needed. Maybe you have a bad cap..... but what's happening sounds normal to me.
 

Greg Gibbs

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Thanks for the info, Todd. There's no evidence of any leak around the cap, so I'm assuming it's OK. That would be a cheap/easy thing to replace, though. I've checked the coolant level when cold and had to add about 1-2 cups (guesstimating) of coolant to the radiator 3 days in a row. Still no change in the reservoir level. It's making me a little nervous, but I'll keep checking and topping it off for now. Planning to crawl underneath it tonight/tomorrow to see if I can spot any evidence of a leak. Fingers crossed that I don't have to pull the fan and water pump again!
 

Greg Gibbs

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You were right, Eddie. Radiator cap replaced and immediately noticed the reservoir level changed (increased slightly) after the first trip. Coolant level in the radiator has remained full since installing the new cap. Thanks!
 

Todd Z

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there ya go..... The cap has two seals and functions.
 

Johnny O

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I replaced my cap recently when I noticed the gasket was kinda hard and not sealing well. Best to replace the cap with a 16 lb unit for a 1998-00 Mustang V6. Helps keep the radiator from cracking.
 

Greg Gibbs

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Now you tell me! My radiator started leaking about a month after I replaced the water pump and radiator cap and has since been replaced as well. (Wish I had known it was about to die when I replaced the water pump!) Luckily, it wasn't bad enough to cause any overheating. That was the first "major" repair I've had to do on this nearly 17 year-old truck with 155k miles. Not too shabby!
 

EddieS'04

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That was the first "major" repair I've had to do on this nearly 17 year-old truck with 155k miles. Not too shabby!
That is good service from these cheap radiators, they make nowdays. your gen1 trac reqires a 16lb cap. What Jon was refering to was. The gen2 trac v6 came with a higher pressure cap. It was causing some radiators to bust or leak before the cap relieved.
 

RMYLY

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I just checked 2010 8cyl rad cap..is 20/lbs correct? Is it advisable to go to 16 lbs ?
 

Todd Z

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Yes, any gen 2 has the 20.
I am running both my v8 and my v6 with gen 1 caps.
 

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