Thats a good idea, I will try that tonight after work if I get the chance. I'm pretty sure my mix if 50/50... I can't remember off the top of my head right now.

Thanks guys for all your help.

 

But, why would it be smoking if it is coming from the heater core? Sure, you would get a water drip, but smoke? And, if the heater is cut off, then there is no water going through the core. I like what or comrade in arms said. Get your head under the dash and have your dad drive while you visually see where it is coming from.
Now, you may get pulled over by a cop because your feet are sticking in the air.

 

I remember back around 1975, my brother had a 1970 mustang that had a bad heater core. Every timg he opened the vent and put the heat on, smoke (steam) came out. That could be the probelme here.

 

By the way, if you're heater is off, water still circulates through the core. You're only opening the dampers to allow air to enter the cabin by way of going through the heater core to heat up the air. I think they stopped using water cut off valves for heat back in the late 50's or early 60's.

 

If you get pulled over, just tell the officer that you know a MP and he said it was ok to do this. Just kidding! Please be careful if you do this, since you probably wont have your belt on.

 

If you get pulled over, just tell the officer that you know a MP and he said it was ok to do this. Just kidding! Please be careful if you do this, since you probably wont have your belt on.

 

I still don't understand how the heater core could cause smoke. Someone please 'splain this phenomena to me. And, guys, remember it only happens at 75 MPH or faster. If the heater core is smoking, it would smoke at all speeds no matter what rate the water pump is running. Or, maybe not. It could be related to the speed the water pump is running. Then again, there should be some residual moisture present in the cabin if it is indeed steam. Anyhow, I guess it is worth a look since none of us can figure out this unusual problem.

 

A friend of mine had an issue with his dipstick tube - it came loose and oil was slowly being thrown out and his engine would smoke - perhaps 75 MPH is the correct RPM for the motor to toss a bit out somewhere? When getting up to 75 MPH you go through that specific RPM range too quickly to notice a constant stream of smoke. At 75 you're keeping the engine at a constant RPM. But this whole not smelling anything is boggling my mind. It could very well be trans related as well, speed-wise I'm thinking. Perhaps at 75 MPH the RPM's are correct for the tranny in 3rd to start whipping fluid out somewhere. But, once again... the absence of odor puzzles me. I've talked to a few wrench-happy friends and they are stumped as well... DAMNED ELUSIVE SMOKE! SHOW THY ORIGIN! LET THIS BEAUTIFUL MUSTANG BE CLEANSED OF ALL DEMONS!

You get my drift.

 

I had a pain in my arm one time when I lifted my hand above my head, so I went to the doctor. After explaining my problem, his advice was, "then don't lift your hand above your head." So, if this is only happening above 75 MPH, "then don't go above 75 MPH."

 

I can't help it Soaring, blame it on my age and the need for speed

And ya, this is only a recent problem, as I've been able to push my car up to 90mph before. And I regularly drive 70-80mph on the freeway.