I have a 1968 Chevelle with a 66 corvette 427 with a set of 502 GM performance aluminum heads. Cam is hydralic .533/.533 and .313/.313, 800 dual feed holley and a set of 2 1/4" Hedman headers backed by a muncie 4 speed and 356 posi rear. I run normal temp around 170/180 which is no problem but if I stop in traffic for a light my temp jumps up to 230/240 in a short time and it's very hard bringing the temp down from that point. I have a 4 core aluminum radiator, 165 thermostat, high flow aluminum water pump. I have the normal fan with a shroud and also a 16" electric fan in front blowing air into the radiator. We did a dye test to see if a bad head gasket, pressure test and everything checked out there. Great flow in radiator when you accelarate. 3 different 165 thermosats were changed and also 2 different guages to make sure everything was good there. Outside temp of the radiator is around 110 deg but the outside motor temp is running around 200. Please if anyone has any ideas on what else can be done, please email me at pauljs0@verizon.net with any helpful ideas. I have had it in 2 motor rebuilding shops to check out my car and that they both agree that with everything I have in place, I should not be running with these hot temps. We are all out of ideas. The car is mostly used for shows and it is embarrasing to be overheating everywhere I go. Lots of chrome and stainless under the hood but I have had that on other big block chevelle and never had this problem with any of them. Heads and motor only has around 2000 miles and I have only had this problem for the last 500 miles or so. Timing is great where it is because if I retard it any more, it is had starting when hot and no spark knock. So timing is as close to perfect without having any starting or spark knock problems.
z71paul

Paul

you stated in your post
I run normal temp around 170/180 which is no problem but if I stop in traffic for a light my temp jumps up to 230/240 in a short time and it's very hard bringing the temp down from that point.
this reflects to a CFM issue .

FIRST OFF
the pusther fan is not the way to go .. blocks air when not in use and 10% less effective then pullers .. pluss its only a
16 inch I would guess and may not be enough CFM

Three major key's to cooling
a efficiant rad to dump the heat generated by the motor .. you have this already .

good flow in the system ... the flow may be good at cruise ..less at idle ..this is where problems can happen ... think of a pan of water on the stove .. more time at the heat sourse or in the block in your case the coolant gains more heat ..your 165 STAT is full open already but low flow in the system ...make sure the water pump it over driven , not under driven .

third --- CFM threw the rad .. this may be your main problem .. mechanical fans have no idea the motors going to 220 and cant do anything to help at idle ... most therm clutchs are only 50% lock up and don’t engage till 200 degrees even with a 7 blade fan .. hayden does sell a 80% lock up unit if you must stay with mechanical ...your not pulling enlugh air to dispell the heat ... trying to maintain stock looks under the hood and combat high H/P are not a good mix .

my suggestion .. just a suggestion if you can do it ,is go electric dual fans with your H/P rating and motor build .. there sensor opperated they know when to do the job .they kick on at 195 degrees ... 2800 cfm right now sitting dead still in parade traffic , sucking that major heat out of your cooling system .

also try thining the coolant to 70% distilled water 30% coolant for summer use .

take a look at these links for ideas
http://www.chevellecooling.com/m3_view_item.html?m3:item=SPAL%20TWIN%2014%20INCH% 20FAN%20KIT

http://www.chevellecooling.com/m3_view_item.html?m3:item=SPAL%20TWIN%2011%20INCH% 20FAN%20KIT

Im sure Scott Weaton will be along shortly to give his suggestions also .

Don

Hi Don,you got me,here i am/LOL!!!!!

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Hi Paul,along with Dons suggestions to maximize airflow at idle which is ivery mportant in keeing in traffic @ idle temps in check you should also chk/adj/and or try the following that can really affect/increase a motor's temp at idle too esp with a perf cam.

* With the cam your running you have ensure you have a least 16 -18 deg base timing .

Make sure to set base timing with idle low like 600-650 rpms to ensure the mech adv isnt partially activated when setting base timing. If running one also ensure vac adv is unhooked & plugged when setting/adj timing too. Then when done setting /chk timing reattach vac adv &reset idle mix & speed too.

Look for 36-38 total with 16-18 base timing,if total is over 38 you will then need to limit/recuve mech adv for 20 deg max all in by approx 2800 rpms to allow the proper base timing of 16-18 deg to be run with your perf cam.

* For street you really need to run a vac adv with a perf cam to add timing @ idle for a cooler running motor in traffic better idle/better throttle responce/better fuel economy/etc.

* Idle mixture set too lean.

* Inadequate airflow thru rad at idle for whatever the reason weather it be a worn out fan clutch and or inadequate elec fan no moving enough cfm,etc.

The 4 above mentioned items are among the most overlooked items tune/setup wise that can increase in traffic @ idle temps when all other items in the cooling system like radiator/fan/fan clutch iff running one etc are all up to proper operating lvl's for application they are being used for.

But there are a few more things to chk out too like for ex:

* Anything blocking airflow thru the rad like an external trans and or oil cooler mounted in front of the rad. If you have that move the ext cooler away from front of rad to free up more airflow thru the rad. If you dont have good place to move the ext cooler to for good airflow away from rad they make small low amp darin elec cooling just forthat situation that work well.

* Like Don stated pusher fans don't seem to cool as well as an elec fan mounted behind the rad inbetween the rad and motor so it has to suck air thru the rad.

* Ensure your running a lrg enough elec fan that can move/pull enough cfm thru the rad 2 idle in traffic. (Call Don and buy a propely rated elec fan for your setup.

* No fan shroud for a stock fixed and or clutch fan setup but thats not an issue in this car with the elec fan you running because they should include their own shroud as part of the comlete elec fan as a unit.

* A Partially clogged rad and or a rad thats either too old/tired or just not lrg enough to disapate enough heat to cool the motor & in that case Don can come to the rescue with one of his high quality Alimitech rad's.

Sinc the motor is heating up at idle only i dont think its an issue with a arm dust shileds and other inder hood weather strip and or seasl missing upsetting proper airflow thru rad and engine compartment in general which would generally affect temp at cruise and isnt near as important when it comes to simply getting proper airflow thru the rad when the car is stopped & @ idle.

Scott

Have you tried a high-flow thermostat?

I have a 1968 Chevelle with a 66 corvette 427 ... I run normal temp around 170/180 which is no problem but if I stop in traffic for a light my temp jumps up to 230/240 in a short time and it's very hard bringing the temp down from that point... We did a dye test to see if a bad head gasket, pressure test and everything checked out there. I have had it in 2 motor rebuilding shops to check out my car and that they both agree that with everything I have in place, I should not be running with these hot temps. We are all out of ideas.

Are you sure its a "66 Corvette 427"? Maybe its a '66 396 that was bored out to 427 bore size (seen/heard of it done many times). The early blocks can often accept the 427 bore, but the cylinder walls might be thinner, causign the higher temps... Whats the block casting number?

Just a thought, but I'd mostly agree with what Don was saying...

FWIW...I put an engine oil cooler on my bored and stroked 427 (496 now) per my engine builders recommendation. it really does drop the water temp too....if the ambient air temp where you live is anything like it is down south here right now - that can certainly affect the thermal efficiency of any cooling system !! also make sure your heater core isnt plugged too...

I also had that problem, at idle temp would climb 220 230 at the heads, I went with a set up from Don (Allumitech) I have the BBC Alum rad and the duel Spal fan set up with shroud, I also thinned the coolant a little put a Robert Shaw high flow thermo 180 degrees, now my coolant temp runs 190 200 at the head thermo runs cool on basic gauge, fans cycle on and off and when those fans kick on the temp drops at least 15 degrees. Prior to this set up I ran a alum rad and mechanical fan and fan clutch and she still ran hot. I woudl start by changing to the electric puller fan set up.

Hey Don Thanks again for everything :)

Twice in my life I have had water pumps that had flow problems at different rpm's, one of them was at idle.
The one that didn't work at idle had almost no flow (under 1 gallon per minute @ 650 rpm), with no back pressure. By 750 rpm it worked fine (5 gallons per minute).

Ron

Ron brings up a very good point here i was well aware of is an issue with some w-pumps but plain forgot to mention it so thanks again Ron for chiming in to remind us of this real issue.

What can happen at times is when there are sloppy mfg practices/machining(esp with respect to w-pump shaft & stamped steel impeller install depth/clearance to backplate esp on cheaper std perf pumps) is if the back plate to impeller(eps cheap cookie cutter type impeller with open back) clearance is too wide that significantly reduces the pumping pressure/flow of the pump like Ron stated which can also cause heating up issuse .

But i have to say thats its a more likely std tuning issues along issues with elec fan being too small cfm wise or rad issues causing his heating up issues before impeller to back clearance issues .

But its possible its a w-pump issue so if all else checks out ok then by all means check for possible pumping issues with your current water pump,you never know.

Thats why i like the Milodon hi flow pumps with good impellers or having the original stock bbc w-pumps of 30-40 yrs ago(065 & 811 long pumps) rblt that still have the stock original good pumping cast iron impellers with closed backsides on them so you can tell the rebuilder to reuse the better pumping cast iron impeller if its not damaged durring rebuild.

But the cheasy stamped steel impellers with open backsides that most rblt and std perf new pumps have these days are a crap shoot for good pumping. That's because when the backplate to stamped steel impeller clearaance it tight they pump decent for a stock to very mild perf street setup. But if the stamped steel impeller to backplate clearance is a little too wide they dont pump well at all like is what Ron very likely ran into which is an issue for sure that does happen once in a while.

Scott

With a high flow aluminum water pump along with the four core aluminum radiator and replacing the 160 deg with a 180 thermostat and I also removed the electric pusher fan, I am now running at idle around 195 and as soon as I give the it gas and start moving, I go back to around 180/185. I believe the 180 stat did the job. Thanks for all your help.