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coolant leaking from tank's cap

8

8000RPM

CEG'er
Joined
Jun 21, 2005
Messages
328
Location
Washington, D.C.
i was driving to work yesterday morning...in traffic, when i saw some smoke coming out of the hood. I pulled over and saw that coolant was coming out of the cap on the coolant tank. I know the cap has a valve in it, that should let coolant out if pressure builds up. but the coolant was boiling in there. then, after the engine cooled down, i drove the car back home and it maintained normal temp while on the hwy. once i started being in a stop and go traffic, the temp started to go up, and coolant started leaking again. now, what can cause this? fan not kicking in? thermostat? water pump? i am, about to troubleshoot, but just need some advise on where to start. Don’t wanna waste time and money in parts that don’t need to be replaced.

thanks.
 
First things to check would be the water pump and thermostat. See if the water pump has shattered in the housing.

Do not continue to drive the car with temps that high.
 
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Sounds to me like thermostat or water pump, though the tstat should have locked in the open position and kept the engine cool.
 
BoSoxBruin said:
If the fans are not coming on when they should though then there would be no way for the engine to cool itself in traffic, even with a wide open thermostat...
Click to expand...

True but if it was just the fans he shouldnt be having the pressure problem causing the cap to leak.
 
Sure he would be having the pressure problem if the fans don't kick on. Without the fans, in traffic, the temperature will keep climbing until it gets somewhere over 212 and the coolant will boil and force itself past the valve in the cap. If I remember my physics right, a 16 LB cap will allow the temperature to go 16 degrees over the normal boiling point of water (at sea level) and then it will boil.

With no fans the temperature could easily get that high.
 
cliff7080 said:
Sure he would be having the pressure problem if the fans don't kick on. Without the fans, in traffic, the temperature will keep climbing until it gets somewhere over 212 and the coolant will boil and force itself past the valve in the cap. If I remember my physics right, a 16 LB cap will allow the temperature to go 16 degrees over the normal boiling point of water (at sea level) and then it will boil.

With no fans the temperature could easily get that high.
Click to expand...

The coolant should make the boiling point of water higher. So it'd have to get pretty hot for the coolant to boil over.

There could be any point in the system that's failing... the fans, the waterpump, thermostat, an air bubble, etc. The waterpumps in the Duratec are prone to having the impeller break. You may start there (by taking a look at the waterpump), and change your thermostat/gasket if it hasn't been changed in awhile. It should be pretty obvious if the fans aren't coming on.
 
Matt R said:
The coolant should make the boiling point of water higher. So it'd have to get pretty hot for the coolant to boil over.

There could be any point in the system that's failing... the fans, the waterpump, thermostat, an air bubble, etc. The waterpumps in the Duratec are prone to having the impeller break. You may start there (by taking a look at the waterpump), and change your thermostat/gasket if it hasn't been changed in awhile. It should be pretty obvious if the fans aren't coming on.
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You're assuming the coolant in his vehicle is up to snuff. Most cars are not. If the vehicle runs fine at highway speeds, it is most likely the cooling fans. A quick test would be to turn on the A/C (assuming it works). The fans should ALWAYS come on with the A/C in use. If they do not, there is a problem there. A t-stat sticking will cause the problem all the time, and a water pump will as well, but not as much when the vehicle is at idle. The key here is that it was only overheating when in stop-and-go, but was fine at highway speeds. If the cap is faulty, that would amplify the problem. Another thing to check while you there would be the expansion tank. Make sure it is not cracked around the threads to the cap. Not common, but hard to find. It won't cause your problem, but could exaggerate it. Good Luck!
 
i changed the water pump a few months ago. i just felt like replacing it because i know that the original could have gone at any point (it was perfectly fine when i removed it). the new pump was also with plastic impeller (from advancedautoparts). I have a colder thermostat which i installed about 2 summers ago. the coolant system was also flushed about six monts ago, and the mixture of coolant to water should be around 50/50. I dont have the golden motorcraft coolant in there, but i dont think that's causing the problem.

how can i check the water pump for broken impeller? if i remove it, then i have to get a new gasket and...i might as well change it again. the thermostat is cheap and easy to get to, so i could change it? but can a thermostat lock up at closed position, and thus cause this problem when in traffic? if i remove the thermostat, can i visually see if it is stuck closed?

i know about the a/c and that fans should work, when a/c is on. my a/c works fine so i will check today. however, if a/c is off, engine on, does one of the fans works at all times or only when needed? i know second fan kicks in at some temperature. with a/c both fans should be running, right?

thank you all for your suggestions. i really appreciate it.

p.s. when the coolant started to leak out, the temp gauge was a little above the middle, so hopefully i didnt mess my engine. but why was the coolant boiling and the temp gauge was not at red?
 
8000RPM said:
i changed the water pump a few months ago. i just felt like replacing it because i know that the original could have gone at any point (it was perfectly fine when i removed it). the new pump was also with plastic impeller (from advancedautoparts). I have a colder thermostat which i installed about 2 summers ago. the coolant system was also flushed about six monts ago, and the mixture of coolant to water should be around 50/50. I dont have the golden motorcraft coolant in there, but i dont think that's causing the problem.

how can i check the water pump for broken impeller? if i remove it, then i have to get a new gasket and...i might as well change it again. the thermostat is cheap and easy to get to, so i could change it? but can a thermostat lock up at closed position, and thus cause this problem when in traffic? if i remove the thermostat, can i visually see if it is stuck closed?

i know about the a/c and that fans should work, when a/c is on. my a/c works fine so i will check today. however, if a/c is off, engine on, does one of the fans works at all times or only when needed? i know second fan kicks in at some temperature. with a/c both fans should be running, right?

thank you all for your suggestions. i really appreciate it.

p.s. when the coolant started to leak out, the temp gauge was a little above the middle, so hopefully i didnt mess my engine. but why was the coolant boiling and the temp gauge was not at red?
Click to expand...
The cooling fan for the 'engine only' only runs when needed. Both fans should run when a/c is on. As far as the Gauge only being a little above the middle, I would say you either have a faulty temp sending unit, or the engine is 'air locked' as suggested earlier and the sender cannot read correctly when not immersed in coolant. For the coolant to boil over, the gauge should be pegged 'hot'. Worst case scenario would be a faulty head/head gasket, they can cause weird problems. Combustion gasses enter the cooling system and create air pockets, causing the gauge not to read properly, heater to not function properly, overheating, etc. These symptoms can be totally random and independent of one another. A good way to test this is with a 'block check' kit. You should be able to rent one from autozone and only have to pay for the amount of test fluid you use.
 
ok. just got back home from work and did some testing. here's what happened. i added water in the tank, and...
engine cold, engine on, both fans nor working. a/c on, both fans work.
left the engine idle for about 15min, temp gauge went right between the N and O of "NORMAL" and was sitting there withough moving. turned engine off for 5 min, i disconnected my batter (i just wanted to do clean my terminals due to corosion), and then installed the battery and started the car. i let it run again for 5-8 min and temp needle went a little after the O of the "NORMAL". At about that time, i noticed the coolant level lifting up, and in about 30 sec, smoke started comeing out of the cap, and then liquid started coming out. i stopped the engine because i was not sure if the gauge was showing correct temp...
i dunno what to do at this point. during the whole time, none of the fans kicked it unless i turned the a/c on...

if water boils, that mean that temp get hot. but gauge is not showing. even if it is not showing, why none of the fans kick in? but they do come on with a/c?
 
i looked at the oil dip stick and the oil cap, and oil seems fine. so assume i dont have a head gasket problem...

how many sensors are involved in the whole cooling system? i just have the feeling that one of them is not working... although i have replace most of them within the past 2 years (the one under the TB looking towards the battery, the one close the DPFE, and the one at the lower driver side of the fans hausing). i just dont remember which one was doing what... damn, this sucker is getting me confused.
 
ok. i did some more testing:
engine on, a/c on, fans on = no overheating - left at idle for 10-15min and 4-5 min kept the engine at 2k rpms

engine on, a/c off, fans off = overheating - in about 4-5 min (fans never kicked in), then turned the a/c on, temp went down.

therefore, i should conclue that it is not the water pump or thermostat, because if either one of them would have cause the car to overhear regardless of whether the fans are working or not. the problem is that none of the fans come on. so, it could be a fuse, could be a relay, or a sensor.
i will check on that tomorrow. in the mid time, which sensors should i look into replacing? the one on fans housing or the one next to the dpfe?
 
This is really strange. If the temp gauge reads normal, and the fans don't come on even though it is overheating one would have to assume that either both the temp sender and the temp sensor are bad(unlikely but not impossible) or there is a big air pocket in the engine, but that normally works itself out with this type of recovery bottle, or something else?. It would be really nice to know what the actual temp is, like use one of those infra-red thermometers and measure the temp right at the sending unit. It would also be nice to know what the computer is commanding the fans to do. If you had a scan tool that was able to read PID data you'd be all set. Man it sucks to do diag with no tools! Also check for KOER fault codes if you can.
 
you have a good point. unless the temp of the engine gets hot so quickly that the gauge doesnt have anough time to respond/show. i always turn off the engine when i see the water/coolant starting to boil. maybe if i live it for a few more minutes the temp needle will go up. when i drove the car home the day it overheated, the needle went above the middle (to the "A" of "NORMAL") and i shut it off...so maybe the sending unit is just slow to read/show on the gauge needle.

yeah, having no tools suck, but now i am the point of checking fuses and relays. i will that tomorrow. and if i dont find any problems there, i will look into some sensors...dunno which ones though...(considering i have replaced them all not long ago)
 
You kind of already checked the whole cooling fan circuit with the a/c test. That's why it's a good quick test. The whole cooling fan circuit is reacting fine when the pcm commands it. The only thing we don't know now is why the PCM is not commanding on when it is overheating.

Both the temp sender (for the gauge) and the temp sensor (for the pcm) react very quickly. there should be very little lag time on a properly working system. in fact, the coolant can't heat up faster than the senders/gauges can react.

Another quick test would be to unplug the sensor. The PCM should default the fans on because it doesn't know what the temp is anymore. If the fans do not come on, you need to check the sensor circuit to the PCM for a problem. The bad thing is you will set a false DTC and the CEL will be on. A scanner would come in handy here, then we could see exactly what the pcm is seeing and what it is commanding. pretty easy test with the right tools. watch the ECT pid, the temp should read something like 250 dgrees to the pcm with it unplugged and -40 with the terminals of the connector shorted together. (or is it vice-versa?) Temp sender does the same thing, unplug it and read the gauge, it should peg all the way one way, short the two terminals together and the gauge will read the other way.

It's been a while since i've worked on one of these for a problem. I'll do some research and get back tomorrow. Everything i've stated here is from (distant) memory and may not be 100% correct, but the testing should be o.k.
 
a few years ago, i had a huge problem with all my cooling hoses. they kept blowing. almost every hose you can imagine got really thin and tore at some point. i have replaced them all, but at the time i was replacing stuff, thinking that the system had too much pressure or was running too hot, thus causing premature wear out of the hoses. In traffic the temp was also going a little above normal, so since it was a cheap thing to do, i decided to get a colder thermostat to see if it would make a difference.
 
O.K I just did a double check and verified what I thought.

The PCM receives the signal from the a/c pressure switch and the coolant temp sensor. The PCM then commands (gounds) the relays as needed. You did verify that all the outputs from the PCM and the Relays are O.k. with the A/C test. Now you just have to figure out what signal the pcm is getting from the Temp sensor. If the signal is correct, why is the pcm not grounding the cooling fan relays? My guess is that the pcm is getting a faulty signal from the temp sensor for whatever reason. The reason could be mechanical, electrical, etc.

A quick but 'rigged together' repair would be to wire a toggle switch to the ground side of the cooling fan relays and switch the fans on when in stop and go traffic. Having said that, it would be better to find out what the problem is rather than bypass it.
 
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