OK,
You've had lots of answers,
There IS AIR in the system-period. Lot of explanations for what is going on but the problem IS AIR. Jack the nose up as high as you can get it, IF you have a heater make sure it is wide open, loosen up the radiator cap-THEN- start it and run for a few minutes. If you watch the flow in the radiator you will see the large air pockets being pushed out!

No secret here........

. . . . all over the engine bay & floor :3DSMILE:


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Kevin...I always ask for the Ideal brand t-stat and i always use a 180 and if you dont have an overflow bottle GET ONE....and use the proper cap also it will help to "burp" the air out of the system.......

Last week I decided to go to work in my 65 fastback, nice cool morning and I hadn't driven it in a few months. Work is normally 200 miles for the day. Left in the early monring, outside temp in the high 50's. Never turned on the electric fan as I was on the highway from the get go, temp ran about 170 or so, which is normal for my car in cool weather..... about mid morning after 2 or 3 stops, got back on the road and temp went down to 145, tapped the gauge a few times, held steady at 145 on the highway, city traffic it did get up to about 170, back on the highway quickly dropped and held on 150.......
Finally made it home around the noon hour and let the car cool off, drained enough water out of the radiator to take out the thermostat out to check it without leaking water all over everything.......

it was one of those high dollar,high flow,balanced thermostats!!!!!!!! I don't even remember putting that one it, must have been some time ago.... Dug around in the shop and found a "standard/OEM" type, 180 with 3 holes in it, tested it and put it in, refilled the radiator and let it warm up, comes up to 180, thermostat opens, temp drops to about 170, then slowly gets back up to and holds on 180..........

Tested the balanced thermostat in the house and it opens fine, just was never closing fully, it's now in the garbage can!!!!!!!!!!!!

I probably put abut 3,000 miles a year on the Mustang, about what the average Cobra would see, so I figured the thermostat may have been rusty, crudded up, but that wasn't the case......

David

Did it overheat with the old thermostat in it, or did you replace it after the initial overheat? Whenever an engine overheats, it damage the wax in the thermostat causing it to be erratic and sometimes stick. Anytime we have an overheat for any reason, every car automatically gets a new thermostat. Due to the difficulties in bleeding these cars I do recommend drilling an 1/8" bleed hole toward the top of the thermostat. This helps purge out air.

Andrei

OK, assuming I have some air in the system, what is the easiest way to burp it? Is this correct?

Fill reservoir, raise the front end, remove reservoir cap, open heater, start car and let it run for a few minutes? I do have a 3/8 inch hole in the 12 oclock position of the new thermostat. So, it doesn't need to open in order for the air to escape the block does it?

Let neighbor's pesky dog clean up the anti freeze that spilled all over the garage floor!

And, yes, I did replace the thermostat after the temp spike incident.

You are basically correct on just about everything. The hole in the thermostat should be no larger than 1/8" otherwise it will bypass the function of the thermostat. After you run the car and feel the coolant getting warm, and depending on your plumbing maybe even some flow, cap the system. Take it out and drive it, then let it sit. After sitting for 20-30 minutes open the cap and top off the coolant if needed. If you did have to top it off, drive it and repeat at least on more time.

Andrei

This is the best radiator filling system for the shade tree mechanic.
It solves all the air problems, and I would not do without one. ;)

You won't regret buying one.

Summit, Jegs, Advanced Auto, NAPA, Sears, ect.....

http://www.amazon.com/Lisle-24610-Sp...=pd_rhf_shvl_1

http://i46.tinypic.com/2mmbmgw.gif

Kevin.....you must have a rather large shop to keep all of your cool gadgets in....

SWEET !!!!!!! I Just ordered one. Although I have no actual overheating problems, I have been plagued by erratic temps for 11 years due to air pockets. I envision this product ELIMINATING the problem!

Thanks for Posting this !!!!! :)


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Problem solved
 

So far, problem solved.

Replaced the 180 thermostat with another 180 and this time drilled a single 3/8 inch hole at the 12 oclock position.

Temps steadily climb to the 80C mark where they stay until I get caught in traffic and then can creep slowly up to 95C where the fan kicks on and sends the temp back to about 90C.

No more spikes to worry about. Mild cruising drops the temps to about 80C and freeway speeds drop it another five to ten degrees. Hard to believe a $7 part can cause such a problem.

As I read this thread - am I crazy for running a 160 thermostat? Should I change to 180?

I prefer a 180. If it's going to over heat, it will do it regardless of the t-stat temp. I just like my oil and my motor a little warmer than 160.

Not really, any part made by man is subject to defects and failure.......

Over the years I learned the hard way to test all thermostats (and any other part that can be tested before installed) before installing them and have found 2 that didn't work right correctly out of the box!!!!!!!!!!!

One opened when it should have and never again fully closed, ever!!!!!!

The other on the third cycle in a pot of water on the stove hung wide open, never to close again, both of these were brand new, name brand parts, it happens!!!!!!!!!!!!!!!

David

I had tons of problems with the Robershaw performance stat, marketed under Robertshaw, Moroso, Mr. Gasket etc... I went through 6 stats to include the previously mentioned "balanced thermostat" before I gave up and replaced it with a run-of-the-mill Stant Super-Stat. The temps hold steady now as they should with no hint of any problems. Cooling doesn't seem to be inhibited either with the Stant.

A purposely blocked coolant bypass will generate heavy temperature swings too as it hinders coolant flow through the engine with a closed thermostat. You'll end up with steam pockets in the heads etc. Drilling one or two 1/8" holes in the t-stat WILL NOT provide you with as much flow as the bypass will, hence the temp swings too. I'd been down that road also.:CRY:

Dave

Do any of you use the cheap summit racing t-stat. Just as good as the other cheap t-stats? They all seem to be pretty much the same design as the other cheap ones.

I ordered a t-stat from Summit some years ago. I screwed up and they sent the wrong one. It's still in my toolbox, I ended up down at NAPA and bought one there instead. :)

the "ideal" brand of t-stat has always worked well for me.....
no extra holes needed...

So I guess that for your application the Summit t-stat is about as good as any on the market. :LOL:

I don't come up with "ideal" anywhere and it's not an easy thing to google, since everyone seems to think their products are ideal....**)