The coolant recovery/expansion tank on my 95 F150 has been constantly blowing out coolant after the truck has been driven and then sits for a short time. I guess this is happening when the heat is highest, and the pressure builds up. I have a new radiator etc. Just about everything has been replaced. I thought it was a leak, but I can see coolant on top of the tank. Every couple of days the tank is empty when I check it. The radiator stays full though. Does anybody know whats going on here? Thanks

 

sounds like you could have a blown head gasket. A blown head gasket will make coloant come out of the coolant reservior.

 

My '89 has done this since the day it was new, Ford never would/could fix it or explain it, I just ignore it now

 

My 92 with a new rebuilt engine, new hoses, new Tstat, new radiator, new heater core, new water pump, and new rad cap, occasionally leaves splashes around the overfill cap. The cap doesn't seal very well, it doesn't need to, I don't think the coolant is simply splashing out over the top, but it is being forced out somehow. It did that on my original stock set-up and the new set-up, that I personally put together, does it also. I watch it carefully, and have given up being alarmed by it. I haven't had to add coolant to the reservoir since the radiator was replaced last November.

If your coolant is old maybe you should consider replacing it, I am not sure if old coolant has a lower boiling point, but it can be checked easily with a 5 dollar hydrometer.

Jam some clean white rags under the reservoir and try to see if it is leaking out the bottom. The rubber hose from the filler neck to the reservoir could be rotted and thowing a fine stream of coolant out. Check every connection with a white paper towel, if there is aleak anywhere then the paper towel and/or antifreeze smell test will help out. If enuf is leaking you should smell that sick sweet smell.

 

If it didn't do it before, you probably have air in the coolant system. Air pockets expand alot when they get hot and will usually push coolant out the resivoir. When the truck cools down, the air pockets shrink, and the coolant is sucked back in. Your resivoir may go empty if its real bad.

There are two possibilites why you have air in your coolant. When it was refilled, the air never purged out of the system completely or, you have a leak that is sucking in air.

Check for diposits around your coolant system, intake, and radiator. If you can't find a leak, just make sure the resivoir is always filled and never goes empty. If the problem doesn't go away, you may want to try using a coolant purge set-up.

 

I think it even did this with the old radiator. Just not as bad. I suppose it is possible that there is still air in the system. If there aren't any leaks, how do I get the air purged out of the cooling system? What is a coolant purge set up? I'm almost positive that there are not any leaks anywhere else. I will do a thorough search again. I don't think it is sucking in air. How would a blown head gasket cause this? Is that because of the possibility of air being sucked in through the leak? There is not any water in the oil or oil in the water that I can see. I would think that I would see that if it had a head gasket issue. One thing I forgot to mention is that the new radiator is an older style copper/brass design. It is also the largest one I could get. I thought that would help keep it cool. With my truck being black anything thats cooler is better. I went this route because I didn't want that aluminum junk with the plastic crap end caps. I've had several of those fall apart on different vehicles that we have owned. Is it possible that the radiator is too large for the recovery tank?

 

I have looked and can not find any leaks whatsoever. Is it possible that the new radiator is too large for the expansion tank?

 

What type of driving causes this. Around the neighborhood, highway, stop-n-go? How long does it take? Will it do it if you just let it idle in the driveway?

 

As far as I can tell this does not happen as long as the truck is running. It happens just after it is turned off. It doesn't really matter how far I drive, just as long as it warms up all the way. Then after it sits for a few minutes (maybe 15) and heats up more and pressure increases I guess it over flows the expansion tank. It even does this in the winter time. Its really not as bad that time of year though.

 

When the engine is cold, where is the coolant level in the expansion tank. It should be at the COLD level. The idea is for there to be enough room in the tank to hold the coolant when it expands due to the engine heating it up. Then as the engine and coolant cools/contracts, it is sucked back into the radiator and the level goes back to the COLD level. If you are filling the expansion tank close to the top, then when the coolant expands, it will overflow the tank. I would pressure test the radiator cap and check the radiator filler neck for a good seal also. I don't mean to sound like you don't know how the tank works but I have seen alot of people just pour water into those things and not pay attention to how high they are filling them.

 

Yeah, I understand basically how they are supposed to work. If it is overfilled it will overflow the tank when it gets hot. I have tried leaving it at cold fill when the engine is cold, but if I do that the next day there is no coolant in the tank. I can see antifreeze on the top of the tank. I always overfill it now. I alternate between anitfreeze and water. That way it can use what it needs to. Do you think that they new radiator might be allowing more coolant into the tank than what it can hold? I have changed the cap about 3 times. I'm pretty sure it is not the issue. Any other thoughts? As I said before, it has been doing this for almost as long as I have had the truck since 1998. It has become worse for the last year or two since I replaced the radiator. I can't really imagine why it does it so bad. I have seen many cars that do this a little bit. You might have to add a splash of coolant once a month or so, but not nearly every day or so. Thats the way this is. One thing I didn't mention is that occasionally while sitting in traffic I can smell antifreeze, so I'm sure it is overflowing the tank at that time. Coolant is too expensive to be adding it like this. The radiator itself barely ever needs any. This has me baffled.

 

Maybe it's time to visit a cooling system specialist, the head gasket may be leaking, as previously suggested.
The exhaust might be getting into the water jacket and causing the overflow.
There are ways to determine if exhaust gases are in the cooling system, pressure tests, chemical tests and plain old-fashioned observation.
I have found that most cooling system diagnosis and repair, that I had a pro perform, was not too hard on my wallet, unfortunately, if the problem is a head gasket, that is expensive.
I checked your profile, the truck looks like it has some nice mods and you have been maintaining it, I would settle this problem ASAP, it is critical to keep your cooling system operating perfectly to ensure the engine lasts a long time. Good Luck

 

Is there a special procedure for bleeding the coolant system? I know when I changed the water [ump on our 90 T-bird it had a special procedure to bleed the air out of it. I'm going to have to do the 95 Grand Prix before winter hits. It also has the same thing. On both cars, there is a sticker under the hood that tells about this. Look for something similar on your truck.
Mike B

 

I dont know what cars and trucks have this, but I know that some vechicles that I have worked on had a bleeder on the block side of the thermastat. Look for something like that on top of the engine. if it dose have one then all you have to do is get the car to normal operating temp (I think it has to be a normal temp), and open the valve up a few sec at a time till you are not getting any air out. GL
Scotty

 

My 92 F150 did this too right after I got it and I decided I wanted to see this happen in front of my eyes.

I got the truck hot by doing stop and go traffic on a hot day and then pulled the truck onto the driveway and turned the vehicle off. The temperature of the coolant will rise immediately above normal operating temperture after the engine turns off --(I have noticed this on other vehicles that have thermostatically controlled electric fans--the fan only comes on immediately after hot turnoff of the engine).

The engine temperature will immediately elevate after hot shutdown and you will be able to witness what happens. I did this and heard the coolant boiling within the radiator and then with a rush the coolant came out of the resevoir and overflowed . This lasted for just several seconds and then the coolant stopped boiling . What caused the coolant to boil??---pressure wasnt maintained within the coolant system. A leaking radiator or coolant system would cause loss of cooling system pressure. My cap was the source of my pressure loss and this fixed my problem.

You said that you replaced your cap three times--I would suggest checking the coolant system for a pressure loss and if this is the case--find out where the pressure is being lost. Make sure that your cap is rated for the correct pressure rating for your truck. I believe that it should be 13 PSI.This rating seems to be surprising low for a truck--most of my other vehicles use higher rated radiator caps.

Test your new radiator caps and make sure that they meet their pressure rated requirements. There are more and more cheap Chinese auto parts out there and it wouldnt surprise me that these new caps are releasing pressure before their pressure rating.

I would also suggest that you have your coolant system checked and make sure that it will maintain pressure within the system. Use one of those "bicycle- pump- with- gauge" tools to check the cooling system pressure when the system is at room temperature. Or listen for cooling system whistling as the system cools down. I have been able to locate pressure leaks before this way in a very quiet environment.

When I went shopping for a used 88 thur 96 F150--I looked at dozens and ALL showed evidence of coolant overflowing from the resevior!!! It didnt matter the mileage nor condition of the vehicle. It had me concerned at first--but I now dont think that it is a problem that cant be fixed .