Invisible coolant leak

[coolbreeze48]

My 97 explorer 4.0 SOHC engine has a coolant leakage problem that is driving me nuts. By all indications there is no leak, yet I am still losing about a quart of coolant about every 125 miles. I have no signs of coolant under the vevicle, no bubbles in the radiator or no excess pressure build-up either. The reservor is not leaking, the system has been pressure tested using 15 PSI air pressure which it held for 45 mins with no leak seen. I am wondering is there any water passages in the intake manifold that could only be leaking during the intake stroke. I know this may sound stupid, but I am at my wits end. Oh, also there is no coolant mixed with my oil so I would assume that wherever the leak is, it is blowing out the exhaust, However all the plugs look nearly the same in color. Could the head gasket be blown evev though there is no indication of this by observing the coolant with the engine running. I have been crawling around under the vehicle more times than my body wants to allow, but I have found nothing. I have read many of the posts about leakage on this site and though - have found some problems similar to mine, I haven't seen any as haunting. If anyone has any ideas I am open to all suggestions. Does the intake on this particular egine have water ports near the intake air ports. I haven't removed the intake so I have no idea as to it's configuration. Thanks in advance.

 

[gtyates]

Could the heater control valve be leaking? Mine was. It is located on the passenger side of engine compartment next to the blower box. has several hoses connnected to it as well as a vacuum line.

 

[coolbreeze48]

heater valve

Could the heater control valve be leaking? Mine was. It is located on the passenger side of engine compartment next to the blower box. has several hoses connnected to it as well as a vacuum line.

I checked the heater valve while the system was under the pressure test and didn't notice any leak at that time. I will double check it to be sure. Wouldn't the valve leak while it was under a pressure test if that is where the leak was, or if the valve was closed at the time of the pressure test would that have kept if from leading? I have a feeling that it is going to be in the intake manifold or in the head/head gasket some how or another. I just don't know how to figure where, or which head it would be, since I can't pinpoint the source of the leak. I would hate to pull the heads and then find that the leak was at a different location. I don't mind the work, I just don't want it to end up being needless, time consuming work. Maybe I'll get lucky, that would be different.

 

[BrooklynBay]

Check the radiator cap & the reserve tank.

 

[jremington59]

If you don't see anything in the oil or coming out the exhaust don't go and start tearing into the engine. I once had a problem similar to this and it ended up being a rotten spot under the clamp on one of the heater hoses. While the vehicle is running, wiggle and twist the hoses a little and see if anything is leaking.

 

[KRAWLER]

Does your exhaust have a whitish color to it when running? If so it possibly could be a head gasket. It could be burning the coolant in the combustion chamber, this could be why you have no external signs of leakage. To help determine what side or cylinder you could run a compression test, if you run across 1-2 cylinders with lower compression those could be your problem cylinders/side.

 

[budwich]

drop some dye in the tank... wait a few "miles"... borrow a UV lamp and presto... you will find something bright somewhere.

 

[coolbreeze48]

Does your exhaust have a whitish color to it when running? If so it possibly could be a head gasket. It could be burning the coolant in the combustion chamber, this could be why you have no external signs of leakage. To help determine what side or cylinder you could run a compression test, if you run across 1-2 cylinders with lower compression those could be your problem cylinders/side.

The exhaust isn't white or steamist, it has some water droppets when first started but once warmed up it goes away. I think I will have a compression check ran to see what shows up.

 

[coolbreeze48]

drop some dye in the tank... wait a few "miles"... borrow a UV lamp and presto... you will find something bright somewhere.

I have a UV light that I use in A/C leak detection, what type dye would I have to use, would any UV detectable dye work or would it have to be something specifically to mix with water and antifreeze?

 

[budwich]

I am not sure if its "system specific" dye... but most auto parts places sell little packets for $2-3 ... at least up in the great white north. I would think any dye works. I used this method to help track down a leak near the driver side front cover.... left an easy traceable trail that was hard to see in normal operation.