Loosing Antifreeze with RPM

[New Lime 69]

Yesterday I took a long freeway trip and found that my engine temp escalates with speed, noticibly!

So I checked the radiator fluid and observed I was low. Everytime I accelerated past 65 MPH the temp would come up and I would lose fluid. If I stayed below that I was fine albeit still a little warm. I have been driving this car for over 20 years and know its pecularities... something aint right.

I checked for bubbles in the radiator and didnt see any. I checked for water in the oil and didnt see any evidence. The timing is a tad off (If I stomp on the accelerator it will knock and ping some). But other than that she should be running perfect.

Its a 69 Mustang with the 250, H/W 5200, Duraspark 2, headers, and MSD... Any help would be great.

Thanks.

 

[BIGREDRASA]

I've had it happen to me. The crack in the head was small enough that only higher pressures caused the bubbling. Check for bubbles when you rev the engine. Might even try butting the car up against a wall, put it in gear, and watch for bubbles as you give it some gas. Hope it's not a cracked head, but I think a gasket problem would show up more readily.

 

[FALCONAROUND]

Ar you still using the original radiator with NO overflow and a single way cap?

I cannot drive my 61 Falcon over about 72 mph or the thing will right up and overheat.... So I only drive about 68 unless some ricer retard tries to pass me, then it's on and the sky is the limit

My falcon's issue isn't quite solved yet, but that's neither here nor there, I CAN say for positive that there is NO crack and there is a GOOD head gasket, it's done this since I got it.

The easiest thing to do is put a good overflow bottle on the rad where it dumps the extra coolant and then as it cools it will pull that coolant back as the block and the coolant shrinks back to a norm.

Then see how hot it actually get's, put a real gauge on it that uses mercury for this test.

Maybe it's time for an upgrade to your radiator.... Mine too for that matter

 

[Frankenstang]

Yet another thought is the water pump seal failing. I've seen water pumps in the early stage of failure purge water out of the weep hole in a delayed manner and thereby relieve pressure and temp. Usually they'll purge under the highest pressure and temp conditions.

If this happens at high mph you're not likely to see it. If you shut the car down when it's peaking on the temp, and wait, pressure and temp rise a bit and you might see it purge then. Most times when the seals fail altogether there is no doubt because of the steam everywhere and the small pond under your car. Of course this is if it's the pump and not a leak/crack or overflow problem as mentioned.