I'll toss this bone out for chewing on and discussion.

91 Aerostar 4.0 E-4WD, original radiator, 213,000 miles

Recently I noticed a small coolant leak on one side of the radiator that could be traced back to an area between the side tank and core. This was a small leak and was only discovered when I noticed a film on the rubber bellow of the recently replaced steering rack. Fearing a bad rack seal, I was pleased to find it was only coolant slowly leaking and blowing back onto the bellow when driving. Over the next few weeks, the leakage increased to the point where a small puddle would form overnight. At the height of the problem I had approximately an 8" puddle form under the front end during a 30 minute lunch stop.

While this was occuring, the normally placid temp gauge crept up one or two notches to the "M" in NORMAL. I had replaced the radiator cap last year and figured this one failed and was not holding pressure. A check revealed the system is under pressure.

Within the past two weeks, the side that originally leaked stopped but the other side began to leak in about the same place, again just a small leak. During this entire 6 week period, I added approximately 1 gallon of coolant to the system and NO additives or sealants. There has been no other strange engine or operating problems during this time.

Now, out of the clear blue sky, there are no leaks, the reservoir remains full and the temp gauge is back to its old position. I spoke with a fellow at the local radiator shop and he showed me the Ford tank seals and explained how they become hardended over time, causing leakage.

I was pretty much convinced this was my problem but now that the leakage has stopped, I'm not sure what to think. If the seals were hardened, I can't imagine how both sides managed to re-seal themselves to the point where they hold under normal operating pressures.

Before I tear down the radiator, I thought I would throw this out and see if anyone else had similar experiences or thoughts on the matter.

 

Cold weather will cause all kinds of wierd leaks where metal & rubber seals meet. It may not leak for awhile & than will start again depending on the temperature. I would change it out. When the weather gets hot it could blow apart at the seams and leave you stranded on the highway & worst case a damaged engine. While doing that replace all your coolant hoses if you haven't. Good insurance. I did mine last year on my 93 4.0.

 

Yes, I would agree cold weather can and does wreak havoc with expansive metals. The only problem here is the weather in Colorado has been unusually warm this winter, seldom below freezing during the day and the van is garaged at night. None of the brutal. subzero temperatures that usually bring on such problems. I still plan on pulling the radiator and replacing those seals. I'm sure there is a rational explanation for all this, but in the meantime, I find the situation a curious oddity.

 

I am right next door to you in Nebraska. The temp is to be down to 1 degree F to night. I have seen it down to 30 below here. Colder here than when I was a year in Alaska. Seen an oil pan blow of an Airforce truck when trying to start it in 30 below.

 

I recall seeing a documentary, possbily about the construction of the Alaskan oil pipeline, where they had to set fires in sawed off oil drums to warm the engines before they would start.

Well, here in the banana belt, the miracle has ceased - the leak
has returned. With forcasted temps in the 40's this weekend, that bad boy is coming out.