NCRaineman

Greetings all.

I've got a bit of a mystery on my hands, looking for insight from someone with experience working on these vehicles.

'05 V6 auto, ~43,000mi

Not an ace mechanic but am fairly handy with a wrench, have torn down and rebuilt a few engines over the years, not to mention countless bolt-on mods to various vehicles. Picked this 'stang up just after X-mas. It gave all appearances of being in good mechanical order, is clean under the hood and has very low miles for a 10 year old car. But now something has come up that's puzzling the heck out of me. I'm trying to wrap my head around it before I take it over to a local shop and say "fix."

Issue 1:
I noticed last week that the coolant tank up front was low, so I bought some of the recommended coolant and topped it off up to the "cold full" line. Checked it a couple of days later and it was low again, so I topped it off again, up to the "cold full" line. I did notice some residue on the lid of the coolant tank by the cap, like it had gotten a bit over full and spit some coolant out. Checked it this morning and the tank level is down again, not severely so but certainly lower than the "cold full" level that I filled it to.

Issue 2:
The heat on this thing is confusing me. It gets down into the 20's here overnight so I let the car idle in the driveway for 10-15 minutes in the morning to warm up and defrost the windows. Temp gauge comes up, heat gets warm just fine. A few miles down the road the heat goes cold and the temp gauge drops, like the thermostat went from completely closed to completely open and all the cold fluid from the radiator went to the heater core. It warms back up as I drive. When I get to the first stop light in town and have to wait for a few minutes the heat will get cold again, only to warm back up as I drive off. Once I'm ten minutes or so down the road the heat stays warm.
Never had a car do that before.

Read about the lovely plastic thermostat housing and its tendency to fail. Have checked mine as thoroughly as possible while it's still attached to the car, not seeing any evidence of leakage.

The car isn't dripping coolant anywhere that I can tell, the engine bay is dry and clean. I don't smell any coolant and I don't see any evidence of seepage around the block, radiator or hoses.

Have dealt with failing head gaskets on vehicles in the past. Checked for evidence of coolant on the oil dipstick, oil looks fine to me. Also am not having any issues with rough idle and am not seeing out-of-the-ordinary levels of white smoke from the tailpipe. Car is not running hot, once warm the temp gauge stays right in the middle and doesn't really move. Considering the low mileage of the vehicle I'd like to think head gasket issues are unlikely.

So that's where am at right now. Anyone got tips or pointers?

Thanks.

JimC

Unless your car is blowing white smoke which usually indicates coolant into the cylinders, check that thermostat housing again. The coolant is going somewhere and can't just evaporate. Usually the split is on the back side and it blows the coolant under your intake manifold.

That could have something to do with issue 2. If there is air in the system from the leak, then your heat will get messed up too.

NCRaineman

Took the car out this morning while there wasn't much traffic on the roads and romped on it good. Checked coolant level after and found that there are all appearances of a leak in the thermostat housing blowing back under the intake manifold. Engine is wet in the area directly behind the housing. Looks like the crack is small enough that it doesn't leak much unless the engine RPMs are up and the cooling system is under pressure. Will get that fixed next week.

Thanks for the info JimC!

JimC

I'm glad you found it. Luckily it is an easy fix and quick (unless you have the Xcharger Xtreme like I had because 2 bolts are covered and I had to remove the supercharger to get to them).

There is an aluminum thermostat housing out now, you can find it on Amazon.