My 65 with 283 automatic runs very hot in city traffic. I noticed this after doing a multi year frame off resto. The engine is rebuilt. It runs about 185 on the highway, but when temps get to 80 degrees and I am moving slowly in stop and go city traffic, it slowly heats up higher and higher. Couple days ago the gauge was about to touch the H mark, so I parked it for a while and later drove home (I live outside the city). It did this last year, so I put a new core in the radiator this winter, but it hasn't done the trick. It runs a bit cooler, but still will probably boil if I had to drive in city traffic at 90 degrees for more than 20 minutes.
I think I need to pull more air across the rad at idle, SO...is there a five blade fan that will fit or work? How about swapping a fan clutch with 5 blade fan from another year GM? How about the flex fan I see in the Year One catalogue? Any suggestions? thanks.

how new/old is your water pump? have you flushed out the cooling system? are you sure your thermostat is good and opening all the way? do you have a fan shroud? what does your timing curve look like (initial, vac adv. and total timing). if your base timing is retarded, it will cause it to heat up some.

there is no reason it should run too hot if all those things are good. I have a pretty stout 385ci sbc in my '65 and even in 120* weather and heavy traffic here in Turkey, it never goes over about 195*

The water pump is older, not new. But if it pumps to hold the temp at 185 on the highway what could be wrong with the pump in city traffic when the engine idles?The engine was rebuilt and hot tanked about 2 years ago, and I have put only 800 or so miles on it since, so it should be fine. I never had the system flushed after assembly, but the rad is new this winter so I am reluctant to spend the 275 bucks the rad shop wants to chemical flush the entire system. The coolant is nice and green with no evidence of rust\scale, when I drained it last week to check it. Changed out a new thermostat for another new one also. It works as I tested it. At 180 it opens in hot water and you can see on the qauge when the engine gets to say 185 it opens and the temp drops at tad to about 180. I am wondering if the engine rebuilder blocked a passage somehow with a gasket or whatever, but I don't want to rip apart the engine cause unless it is a last resort. I set the timing with a good timing lite many times and it runs great. Set to factory specs. I guess I could try advancing the timing a bit if you think that might cool it a few degrees in city traffic. I just read my SS Restornatio book and it says some models of 64 and 65 chevelles came with a fan clutch, AC cars or higher performance 283 and 327's. Mine is base engine 283 so the 4 blade steel fan is correct for it.

I had the same problem with my 283 after a rebuild. Was the engine bored out when it was rebuilt? I've heard of a few cases where the cylinder walls were thinned out enough by cylinder boring that they couldn't transfer heat efficiently after a rebuild. There is also a possibility that a gasket is blocking a water passage. The final possibility is if you had the radiator recored or repaired, they may have blocked off some of the water passages in the radiator, causing it to be less efficient. That said, I probably would start off with a larger fan and a shroud since it is the simplest fix. My problem turned out to be blocked passages in the radiator after a recore.

I did have the rad recored this winter, and the heating problem was a bit reduced after the recore, so I don't think the recore causes it. My engine was bored 10 over in the rebuild so that could be an issue. Maybe the rebuilder used a slightly incorrect head gasket and blocked a water passage??? Don't know much about water circulation in the block and heads so I am guessing here.
One thing I didn't mention earlier, is that the rad cap appears to be weak and allows coolant to burp out the overflow tube after slowing down from highway speed to an idle. I notice a few drops of coolant at the end of the overflow tube and a few drops on the pavement if I stop soon after highway speed cruising, say to go to a gas station.
This morning I put on a new rad cap and will test it out today to see if it stops burping out coolant. Maybe the fix is as simple as a new rad cap. I will report back. But it's cool here today, say only 70 degrees so I can't find out if it does the trick until it warms up more here (Canada).

that could be it. if your cap won't hold pressure, the water will boil at 100C or 212F (give or take based on atmospheric conditions and how much pressure your cap will hold). if the cap keeps the system pressurized, the boiling point goes up which keeps the water in the system.

if your motor was hot tanked, i doubt it is plugged up with gunk.

do you have a fan shroud? that helps too. if you are gonna play with the timing, do a little searching and reading up on ignition curves or setting timing first so you know what you are trying to do. if you are at 6*btdc, that is pretty retarded for most sbc's, that could be a part of the problem, but if you bump it up to say 15*, be sure to check your total mechanical advance so that it does not end up more than 36* or so.

My 65 with 283 automatic runs very hot in city traffic. I noticed this after doing a multi year frame off resto. The engine is rebuilt. It runs about 185 on the highway, but when temps get to 80 degrees and I am moving slowly in stop and go city traffic, it slowly heats up higher and higher. Couple days ago the gauge was about to touch the H mark, so I parked it for a while and later drove home (I live outside the city). It did this last year, so I put a new core in the radiator this winter, but it hasn't done the trick. It runs a bit cooler, but still will probably boil if I had to drive in city traffic at 90 degrees for more than 20 minutes.
I think I need to pull more air across the rad at idle, SO...is there a five blade fan that will fit or work? How about swapping a fan clutch with 5 blade fan from another year GM? How about the flex fan I see in the Year One catalogue? Any suggestions? thanks.

some 64/and 65 models had no shroud ...does yours ??.. if not you may retrofit a 66 plastic unit to yours if you mount the rad to the core support and eliminate the spacer box .

this will help alot as your problem is CFM at idle .

she runs cool down the road .. but heats up at stop and go ..means you need more air threw the rad .

Don

Don, your suggestion is what I was thinking I need. I do not have a shroud now, but if a 66 plastic unit will fit I may try and find one. If I could pull more cfm through at idle I think I would be okay. What is your thoughts about a five blade fan if I find one to fit. I think the higher perf V8's from 64 and 65 used a 5 blade fan. Maybe a 5 blade fan without a shroud will work?

A stock to mild perf 283 should not be a cooling problem esp with a newly recored rad.

Since it temps are ok @ cruise and the motor only get's hotter in traffic try checking these things out.

1a) Start motor cold with rad cap off and then get it heated up enough to show hot on temp gauge . Then insert an automotive ac type thermometer into hot collent in rad filler neck while its running to see if it's in fact running too hot or not.

Doing this above test will verify if the temp gauge is on the mark/reading correct or not before trying to fix something that's not really borken.

If temp stays at 200 degt or below when checking the coolent temp in rad filler neck when hot sitting still for like 15 mins or more your ok and there's no need to go any further IMHO.

But temps over 200 deg maybe 205-210+ deg f when sitting still is not good and in that case check out te following.

1) Ensure t-stat is ok even though since its not running hot at cruise and only runs hot after being in traffic a while i dont thoink its the t-stat,running hot in traffic only is generally collectively a tuning/airflow thru rad at idle issue.

2) With your Rblt engine it "very likely " has a very mild aftermarket non gm cam like comp etc that needs a lot more(3x-4x more) base timing then the 4-6 deg bsae timing a 283 with stock gm cam uses.

So even with a very mild aftermarket cam adv base timing to at least 14-16 deg and if the motor respnds well to more base timing with better throttle respnce and idle (which i bet it will) leave it there/look for 38 total tops.

If motor runs well with 14-16 base timing but total is over 38 then you will need to have mech adv in dist limied/recurved for 20 deg all in by 2600-2800rpms for more umph/trq in this case esp with small 283 likley running tall highway gearing & glide trans .

Have the idle low like 600-650 rpm to ensure mech adv in dist doesnt mess up base timing setting,vac adv also needs to be unhooked & plugged to when setting base timing.
whjen done setting timing rattach vac adv & then reset idle speed & mixture.

3) Also,make sure to attach the vac adv vacuum line to full intake vacuum all the time after setting the base timing.

4) A std duty and or hd (thermostatic fan clutch/not cheap crappy workng non thermal fan clutch that runs a lot more) along with an with opt 5 blade fan used in 1965 for ac cars and or car's gettign opt hd cooling should do the trick just fine. You can get the fan & fan clutch from Ground Up etc.

5) Do you also have the kinda 55 gal barrel looking fan shorud the 65's came with that had AC and or HD cooling option? If needed,you may be able for find the fan shroud in Ground Up.

6) Check idle mixtrure to ensure its not set too lean.

7) An extreem vacuum leak casuing very lean fuel calibration issues can also increase enine temps but thats not likely esp if the motor is running well at idle & at cruise to other then just getting hot after being in stop/go traffic for a while.

Things like retarded base timing,not having vac adv on full it vac all the time,no fan shroud esp if running the stock 4 flad fixed fan that doesnt pull much thru a rad even with a shroud let alone without a shroud,etc will collectively make a motor run hotter in stop/go traffic .

Get these things in order and i bet you will reduce/improve the in traffic temps enough to fix the problem.

Scott