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Discussion Starter #1
Hi folks
My 66 Mustang GT is running high on the temp gauge and today blew down for 30 seconds after I shut it off, making a fine sound during the event. Car ran fine, otherwise. It’s the original 289 but the radiator has been replaced. I’m assuming a bad water pump. Not sure that has ever been replaced. Both upper and lower radiator hoses were hot, as normal.
Anything else that would cause this, like just a thermostat?
 

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Nowhere near enough background info. Is the car new to you?
 

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Discussion Starter #3
Sorry...I’ve owned for five years. It has PS and A/C. I did see someone discussed timing. I believe mine is fine. I adjusted it last year, about 200 miles ago.
 

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Discussion Starter #4
I’ll also add I’ve noticed some minor coolant leakage under the passenger side of the fan. The overflow is on drivers side of radiator cap.
When cool, the coolant level is usually below the radiator fins. I have added coolant a few times in past year to get level correct, just cover fins. Usually added 4-5 oz.
 

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Since you had no way to tell the exact temperature, if you had the radiator too full, you'd get a little coolant blown out the overflow hose. Find a way to check the actual engine temp. It could very easily be a thermostat sticking closed.
 

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Your issues could be limited to the slight leak and a sticking thermostat.......
It doesn't cost much to check out the thermostat situation. If that gets it you could plan your next PM as
investigating the water pump situation. (R&R to inspect and then resealing it to the timing cover)
 

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Discussion Starter #7
Okay, thanks
I’ll start with the thermostat. I’m guessing a good flush might be in order, too. I just read that there are a couple plugs to remove in order to flush the block. Can that be done fairly easily? Or should I just replace the WP if going through all that?
 

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More info needed.... First, the leak. ANY leak is not normal. Grab a cooling system pressure tester from your local auto parts store to isolate the leak and fix it. If it's the radiator, leaks are usually caused by either damage or corrosion. If corrosion then consider recoring or replacing the radiator. Leaks from the water pump "weep hole" indicate that coolant has made its way past the seal and into the bearing cavity. Time to replace the water pump.

Your '66's Autolite 4100 would have been equipped with a hot idle compensator in the air horn if factory air or in the PCV line if dealer-installed air. If neither of those original parts is present anymore and your heating issue is more or less when stopped idling or in traffic then your heating problem is most likely related to airflow through the radiator when stopped and a slight increase in idle speed may solve it. An electric throttle kicker or an atmospheric-vented DVCV plumbed into full manifold vacuum is one possible solution. The '85 5.0HO also used an in-the-PCV hot idle compensator so you might find one of them out there somewhere.

In the rest of the cases, a bit of overheating can also be traced to insufficient spark advance, especially at lean mixtures.
 

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Discussion Starter #9
Thanks for the detailed info!
The A/C is dealer installed Ford, but no hot idle compensator in PCV line. I’ll check that out.
The leak is more correctly located engine side of fan on passenger side.
I don’t see any leakage from lower hose. Does that, typically, indicate the weep hole?
 

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Thanks for the detailed info!
The A/C is dealer installed Ford, but no hot idle compensator in PCV line. I’ll check that out.
The leak is more correctly located engine side of fan on passenger side.
I don’t see any leakage from lower hose. Does that, typically, indicate the weep hole?
A leak on the passenger side, behind the fan, is likely to NOT be the radiator or a connection at the radiator. A pressure test should find it.
 

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Discussion Starter #11
Like Columbo, just one more question...where are the coolant block drains?
I plan to flush everything and replace the thermostat before I dig deeper.
 

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I'm unaware of any drain plugs. The block freeze plugs are located (of course) near the motor mounts and at the rear. Two on each side, one at the back on each side to total 6.

At least this is what I've learned from googling "289 freeze plugs." I'm considering the cost/benefits of pulling the engine, knocking out the plugs and doing a full pressure wash of the lower end.
 

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When my 289HP was rebuilt years ago, I put radiator-style petcocks in place of the plugs. However, it is totally unnecessary to drain the block at these points to clean it out.

760896
 

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Be careful when substituting radiator petcocks for the original plugs on the block. I've had them loosen up.... be sure to safety-wire them closed.
Ask me how I know.
 

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Be careful when substituting radiator petcocks for the original plugs on the block. I've had them loosen up.... be sure to safety-wire them closed.
Ask me how I know.
Whenever I pull the block drains I replace the plugs with pencil-type zinc anodes.... I don't plan on ever having to remove them again.
761014
 

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Discussion Starter #16
Thanks, folks
I’ll do a more traditional flush and then again with the thermostat removed. I’m guessing there may be some crud in there. I think I’ll leave those plugs alone.
I watched a video on WP replacement. I’ll go there, if needed. That’s a good day’s work for me!
 

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Discussion Starter #17
A little more info. I just drove it about 15 miles in 25 minutes. Mostly 45-55mph with a few stop lights. No overheating, but I left heat on.
I measured some temps with my infrared thermometer, with car idling. I got 230F before thermostat and about 205F after. Top of radiator was 220F and bottom hose was 190.
Also, I do have a shroud and six-blade fan.
I still plan to do the flush, replace thermostat, and look for that small leak.
Do the above temps tell anybody anything?
 

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A little more info. I just drove it about 15 miles in 25 minutes. Mostly 45-55mph with a few stop lights. No overheating, but I left heat on.
I measured some temps with my infrared thermometer, with car idling. I got 230F before thermostat and about 205F after. Top of radiator was 220F and bottom hose was 190.
Also, I do have a shroud and six-blade fan.
I still plan to do the flush, replace thermostat, and look for that small leak.
Do the above temps tell anybody anything?
I would expect to see a much greater temperature differential between the upper and lower hoses.....
 

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Discussion Starter #19
Well, I took the bottom rad hose off and only got about 5 quarts out... oops! I thought I was filling it to top of fins, but must have been wrong. I’m assuming low coolant level may have caused my temp issue, correct?
I took the thermostat out and backflushed through the hole and didn’t get a lot of crud out. I’m debating on doing the vinegar flush...thoughts?
 

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Discussion Starter #20
Okay, I realize I need to break out the dunce cap if I was really running with only 5 quarters of coolant (seems I was).
Beyond that. I did the acetic acid flush and it is soaking now. It took about 3 gallons to fill it to a couple inches below the cap. I drove it a few miles and then it ran for another 25 minutes in my garage, varying the rpm.
The max temp I got with no thermostat was 167F. Does that sound about right?
Also, I heard the WP make a little noise right after I started it. It quieted down after a minute. Was that likely from air, or might that indicate something more? Thanks!
 
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