Overheating at freeway speed

charliecurrie

Well-known member
My '66 stock 200 (except for Weber two barrel and DSII) has developed a new quirk. At freeway speed, the temp gets up to 204+ range (temp gun pointed at thermostat housing) and 154+/- where the bottom hose is attached to the block. it also starts belching a little coolant. This is something that has developed in the last 4 to 6 weeks. When I get off the freeway and drive at 40-45 mph, it cools right down - even in stop and go traffic. The only thing I've changed in that time is switch from 91 to 87 octane, which has made no difference in performance.

What do you think?
 
The difference between the upper and lower radiator hoses shows the radiator is doing its job. If the radiator cap is still good (it might be a bit weak), also the hoses are in good condition (i.e. Not soft and or is collapsing) plus you have a properly rated T Stat installed of at least 180 to 194. The 204 isn't all that hot these engines they were designed to run in the 190 to 210 range so it should show it just a little above the mid range on the gauge. If the above parts check out as good then what you should do is install a coolant recovery system / overflow tank for the radiator overflow tube (If you don't already have one) to catch that belching coolant. Good luck (y) :nod:
 
Thank you for your quick response. Everything you mentioned is in good order. It's just that this condition is a change from it's passed performance - always ran cool - 165-180 range - freeway or stop and go. So I'm just curious as to what happened to cause this change.

This is an original, unopened '66 engine with 75k +/- miles on it.

My friend who built and ran dragsters and sprint cars would tell me, they always run best right before they blow...and, this little engine runs real good. Ha
 
last flush'n fill?

May B wanna drain it and get something caustic in there, flush, assure a 50/50% coolant replace (w/o adding air)?

IDK, may B a chunk broke off in there, or it's just gettin sludgy?
"Hi way speed" 2 me means stress but also plenty of wind blowin by the fins...

The 'overflow' is normal (@ stress). The temp U report not extravagant...
 
Thanks for responding. I kinda have the same suspicion - something suddenly is partially blocking the flow in the block.

I'll give the flush n fill a shot.
 
try a double flush (chem treatment 2X) and the "2 way" (i.e. in each direction).
Just get the "bad stuff" (Chemicals/slough) into a container (for environmental protection) 1st.
U may B surprised by what U C. Esp if you don't do the every-3-to-5-yr maintenance.
(y)
 
Thanks again, Chad.

I'm not familiar with the "two way" / "both directions" flush. Can you explain it so a six year old can understand it. Thanks.
 
no, it's nother search function thread.
But use a hose for 'each way': 1st in typical place (up top) then dwn below. Some 1 w/better key board and english lang skills can explain if U don't C it in the search.
 
Hi, you may as well change the thermostat while you are working on it. Maybe the old thermostat is not opening all the way.
If you can feel the front of the radiator, or shoot it with the temp gun look for cold spots which indicates a blockage. Good luck
 
Thanks, B Ron Co - It appears, after a going over, it may be air in the system. I ran it for a bit with the cap off - ran the rpm up around 3k (just a guess-timate) while watching the temp gauge. When it slid past it's usual stopping point, I got out to check to see if the thermostat had opened and coolant was moving passed the fill spout. I had lots of frothy coolant with some bubbles trying to escape. I started rocking the car back and forth, working the air out. Ran the rpm back up for a bit and repeated the rocking. Did this 3 times before the coolant was clear and moving across the radiator. Repeat the process 3 more times until the froth/bubbles stopped appearing. During this whole episode, the temp gauge stayed put and the temp gun consistently read 177+/- at the thermostat and 143+/- at the return hose.

I'll have to take it for a freeway run to see if that made a difference. Hoping.

I noticed after reving it up and then gooseing it, I would get white smoke from the tailpipe. I changed the oil about a week ago and there was no signs of water in the oil. I've also been checking the level daily since then and there's still no signs of water. What do you think?

Thanks again for your response and suggestions.

Charlie
 
charliecurrie":2xl6aqdc said:
... I had lots of frothy coolant with some bubbles trying to escape...

I would get white smoke from the tailpipe...

Sounds like it's time for a compression test on all cylinders
 
Lazy JW, Thanks for the input. Compression is low - low - but even across all cylinders. It's going to get torn down eventually, but it just runs too good as is, and I have a garage full of parts to play with in the mean time. Well, my wife says it's full, anyway. But, at the moment, my 99 year old mother needs 24/7 care, and I'm it.
 
When I see bubbles in the radiator, it rings a warning bell in my head; possible head gasket issues or cracked head.

I fully understand how the "cares of life" can get in the way of our hobbies. Do take care your Mother (y) :nod:
Best wishes,
Joe
 
Thanks for posting an update. I hope that solved your overheating. Usually I bleed the air out of the system with the front of the car jacked up, on ramps, or anything that raises the front of the car. Then just run the engine with the cap off.

Hopefully, it is not the head gasket. If you are going to do a rebuild soon. Then BlueDevil makes some nice "BandAid" products to get you by. https://store.gobdp.com/products/
 
Never discount the simplest causes and easiest solutions.

I have to go back to the first responder Bubba 22349 because the cause and the solution was in his response.

Yesterday, after bleeding the system the day before, I went to the store and it started heating up quickly - city streets, light traffic, 8 miles +/-. When I parked the temp gun was reading 154 and it was puking coolant. I thought this ain't right. So on the way home I stopped and picked up a new cap.

Later when it cooled down, I went to see how much coolant I lost and check the cap. 4-5 oz is all. I got out the new cap to compare it with the old - the spring on the old seemed a pound or two lighter. I turned the caps over and lo and behold the rubber gasket at the bottom/top - depending on how you look at it - of the cap was gone - metal to metal does not make a great seal under pressure. It must have loosened and fell off, unbeknownst to me when I did a fluid check last week when I changed the oil. That's why the change in how it operated happened so suddenly an out of the blue.

Radiator Cap!

Simple, cheap and easy.

Don't over think the problem - I'm the worst offender.

Thanks to all who commented and all the good advise. Learned a few things I didn't know, and that, I'm sure, will come in handy in the future.

Charlie
 
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