The entire cooling system (except for the
radiator) is made up of plastic
parts, linked by rubber
parts. These cars NORMALLY operate at 220F coolant temp. You may have noticed how, when you turn on the fan for outside air/ventilation, it is always WARM. These cars run a VERY high engine compartment temps. So much that the entire firewall, and the components in it (the ventilation system) get warmed up. Plastics must be carefully Engineered to be able to withstand this environment (I am one of those Engineers). The long and short of it is that virtually EVERY component in your cooling system should be replaced to address this as they WILL fail, and it seems that 60-80k miles is the useful life of these
parts.
As for leak detection, a static engine is a very different beast than a running one. My '96 Mustang GT (first year of Modular engine), like clockwork, blew the
intake manifold water crossover pipe literally weeks after I received a notification that I should go to my dealer and have it exchanged. Ford calculated that it was about to blow because of a molding defect where the plastic was thin and the pressure of an engines' coolant system under wide open throttle, plus the high heat would weaken the plastic. I was entering the Freeway and hopped on it and suddenly a cloud of steam shot out of the hood, temporarily clouding my windshield. I had it towed home and replaced the coolant. At idle, no visible leak, but tweak the throttle and there it was, a 3-4" "seam" would open up and water stream out into the VEE of the block.
I replaced EVERY component in my 2004 (70K miles) with new Ford
parts two years ago. It's very involved because the
intake manifold must be removed to get to a hose that sits in the front of the valley between the heads. About $1K in
parts.
Some of the symptoms that warned me there were problems:
1) smell of coolant during and after shutdown
2)
coolant reservoir needing top ups
3) no evidence of puddles/leaks under car
4) after shutdown, electric
water pump would keep running, it turns out for longer and longer periods before battery finally died which prompted my investigation for root cause
It's VERY annoying that elements on these engines which in earlier generations of American/Japanese/European cars rarely gave anybody trouble. Main reason was they were manufactured out of brass/aluminum/zinc/copper. Metals can easily take the heat/pressure/cycling between hot/cold for almost life of car. "Engineered" plastics where introduced under the hood in the late 80's/ early 90's to cut costs. We all know the T'Bird was rushed to market with the looks of the car as the number one priority as it has MANY Engineering failures that should have been tested/developed/eliminated out of the car before it hit the market. The cooling system was one of them.
I feel like if you are going to replace any component, replace ALL of them.
Part cost is a non issue compared to what you will pay for repeated labor as each component starts it crack/pinhole leak, steam escaping, with you by side of road.
