OP Update: Bad news
 

The bad news:
Cruising the highway speeds shoots the temps up. It never breeched 240 (probably cause it was a cool 75 deg out that day), but came damn close.

I'm thinking that the radiator just cant keep up with the high rpms.

Note:
Highway speeds = A sustained speed at or around 70 mph with an rpm of about 3750

That's good news, tebok. My '67 is in the shop awaiting the arrival of a Dewitts with electric fan. Hope my results are as good as yours. My car did pretty well with cooling unless I ran my A/C (Vintage Air) in stop and go traffic with 90+ outside temps.

[I just read your "bad news" message :( ]

-- Steve

Something else is happening to you. I have new DeWitts and at cruise 70+ at higher RPMS and it cools right down to stat temp. I'm having a bit of temp creep at idle so am checking fan clutch.

run a block check with liquid that changes color to see if you have a combustion leak.....jmo.....:cheers:
have you changed the water pump?.....sorry you are going through this

Thanks for your input, but please read the thread through before posting.

Both these checks have been done.

I've been following along. Just a FYI. I have a zz383 with a Dewitt radiator and 3:55 rear end. 180* thermostat. Stock fan and fan clutch. Mine runs 180* ALWAYS. Stop light to stop light, 90*+ air temp, 75mph for 200 miles on the highway etc. I know this doesn't solve your issue but you should expect better results.

Dennis:cheers:

sorry, the thread is too long and it rambles, i will just stay out of it to avoid further confusion but do wish you luck and will assume all the possibilities have been covered as to blockage, combustion leaks, backwards fan, water pump and rotation collapsed hoses and the like....:cheers:
i will tune in at times to see if you solve it....:rock:

If it's the exact reproduction of the original Harrison stacked plate aluminum radiator you purchased from Dewitt and installed, you have the most efficient (from a heat exchange standpoint) radiator that will fit in that OEM space. And is the same radiator that these cars were sold with when new, so it is definitely able to keep up with higher RPMs. (Also the same radiator I have in my 65 L76 (365 hp), which I can personally attest to being able to run at highway speeds with a "steady 180" showing on the temp. gauge.)

It is quite likely you had multiple causes feeding into your initial overheating condition. I did too. For me, it was a combination of the wrong radiator, poorly functioning aftermarket carb, clogged cooling system, and airflow issues (including airflow through the entire radiator impeded by a previously-installed dual fan kit, which was replaced with a proper fan and oem fan shroud) - all were contributing to my situtation. In my case, the first thing I did when tackling this issue was replace the radiator with the exact replica unit from Dewitt, which helped, but did not cure, my overheating situation. So I feel for you - been there. You have certainly addressed the radiator piece, and now can focus on other contributors.

With all that said, you must be extremely frustrated. I certainly was, when I was in your shoes.

Have you checked if the fans are blowing or sucking air? If your fans are turning in the wrong direction they will help cooling the radiator in your garage, but when they are on at highway speed they are blocking the airstream through radiator.

I agree Dennis, that I should expect better results.

I'm coming to the conclusion that this isn't a simple cooling issue and that it's internal. The car runs well enough now that I can enjoy it and that's most likely where it will stay until I have the time and money to deal with the motor internals.

Good point!

Yes, I have confirmed that the fan is pulling as designed.

Well, the equal of that DeWitts radiator for my '61 car keep my 427 SB cool, though temps do creep up under full throttle passes down the 1/4 mile.

You have verified that there is no head gasket leak, you have a new rad and water pump. I would try one last little thing, even though your Tstat is new, it could be bad. I had a new Tstat fail, causing my car to overheat at highway speeds.

Take it out, put it in a pot of boiling water and make sure it is fully open.

Perhaps that .060" overbore, is simply too much, on your motor. Are you sure it is only .060" over, and someone didn't get creative trying to get more cubes out of it? Too thin of a cyl wall will give you high speed overheating.

Doug

I'm afraid you most likely are correct. The info I posted here is all that I have on the rebuild. I will certainly keep the numbers matching motor with the car, but maybe I'll swap it with another down the road some day when I have more cash. Time will tell

If it really is matching numbers, as the motor that came with the car, and not an e-bay restamp conjuration, you can always have the block sleeved. Just make sure they don't deck the numbers off.

If you just want to drive it, find a 327 or 350 and drop it in while you contemplate what to do with the original block.

Doug

At the first of this thread, it was suggested you double check your new thermostat. I don't recall you ever confirming you did. But maybe you did.

I could agree that thin cylinder walls will bleed more heat into the cooling system but doubt it would cause your remaining problem.

Re: the t-stat and the question of whether it's not opening, suggest using Mr. Gasket #4364 (the former Robert Shaw "fails open" t-stat in a 180 degree version). End of such worries.

Also wonder about the lower radiator hose possibly collapsing at high water pump speed. If replaced already maybe got a soft one, worth a try (although I loath replacing my lower rad hose, a real PITA). If trying that, use something like Paragon pn 1733 (correct hose, looks el correcto, and includes the spring inside to keep it from collapsing.)

Well I will just add my .02 here just because, I have been following this thread from day one and I'm up to date on everything you have done or tried.

So after all that if it was me this motor would now be setting on my engine stand. First thing I would do is remove the freeze plugs and have a look see inside the block for any blockage or heavy scale buildup. Next on my list would be a complete teardown and rebuild to stock specs. A 327/365hp motor is not something special and should run 180 degrees all day long. I had a 66 with a plain Jane 350 hooked up to a 30 year old stock radiator and this car never ran over 180 period.

Now the above might sound extreme but I’m a extreme kind of guy when something like this gets under my skin. I’m in the baby steps of dialing in my 427 on a run stand and I too am having temp problems right out of the gate so I feel your pain. But that is another thread for another day.

Hang tough, you will win this.

Dennis

If I recall where you have been already, Timing is good, Radiator is perfect now, water pump is replaced, Thermostat has been checked/replaced, no air in the system.
Engine passed the sniff test so no combustion in radiator.
You are running out of things that could cause this.
Now the remaining problem is high temp at freeway speeds only?
Thousands of 327's ran at .060 over with no heating issues, even in work trucks so I don't lean toward that.
Was the block flushed? I know there was lots of talk about it, did it flush and what came out?
Exhaust excessive back pressure can cause heat issues. Hard to test but worth a check.
Normally if you have this kind of back pressure issue you would also notice the engine power falling off.
With 4.11's spinning 3,750 you might not notice a 10-15% drop in power.
Did you pull the plate off the back of the water pump to inspect the impeller.
The low price units are not positive displacement and it may cavitate at the high RPM's.

Thanks Dennis. I agree with what you have to say and am leaning that way. I dont have the resources at this time to pull the motor, but it should make a nice winter project. You're right, it's gotten completly under my skin, but in the mean time I'm looking on the bright side. Something isn't right, but it's not causing any damage now and can be enjoyed at a non optimum level. For not, I'll take that.