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Gets too hot in traffic

14K views 68 replies 18 participants last post by  Blueraj 
#1 ·
My 69 ss 396/375 gets too hot in traffic, ok when driving. Correct radiator, fan, thermostat, etc. All new. Has vintage air but I've not been using it lately. Another problem. Maybe I can add an electric fan if it will fit? Taking the thermostat out may be an option but I'm not sure about that? The car seems to be getting too hot but does not overheat. Gauge goes into the red until I start driving away from lights and stops. Gauge seems correct per a temp gun. Any ideas?
 
#2 ·
Stock fan?
The stop lights in Honolulu are some of the longest lights I have seen (only Las Vegas feels longer)
The stock fan just might not be able to keep up..?
I had a similar issue with our 68 and put a flex fan on it to improve the pull thru the rad. (now old technology)
Adding electric fans might be of assistance, but first I would make sure you have a good thermostat. (dont remove it) Then think about taking the Rad in to a rad shop and getting it boiled out. A good flowing rad should keep that engine cool even in Hawaii. 3 core rad? if not ask the rad shop about re-coring.

Hope you get this sorted out, nothing worse than a hot engine while trying to "cruise" between red lights
 
#3 ·
Do you know how hot you're running? My 396 runs between 190-210. I have electric fan and be cool alum radiator and its hard to keep it at 190. Most days in california it runs 200. You might want to get an aftermarket temp gauge just so you know exact temp it's running at. I swapped my console gauges for full sweep electrical to know exact temps.
 
#9 ·
The stock GM cooling system even on todays standards is way over built...
U have new radiator, pump, clutch and stock fan with shroud...and new hoses...Correct?
I gather your symtoms are its ok while moving and gets hot idling correct?
No has nothing to do with thermostat, and if take it out without a restrictor it will run hotter....
In saying that , a faulty thermostat will cause your symptoms.
Buy a new one any way...a GM 180 deg, correct for the application...and test before install, dont assume it is ok....
electric jug water, hang the thermostat in it cold and heat it up, with a thermometer for when is open.
While at it, do the same with the temp gauge sensor, start cold, ground the body, then u can relate the postions of your gauge needle to real temps....And varify temps

Generally moving ok and idle gets hot is blocked/ restricted cores, and/ or no shroud...and a rare long shot, the impeller in the water pump has spun on the splines.

There are a coupe things that can make ppl think its getting hot when they stop at an interesection...
Partuarly noticable after a highway run the hit the intersection and the needle climbs.....if u increase rpms to a fast idle temp drops... that is normal....it will also drop if u sit there longer....what happens is there is a lot of heat in the block/heads, then water pump suddenly goes at a slow speed leaving water in a hot block to gert very hot... this eventually moves past the temp sensor, gauge goes up, into the radator cools and takes a while to get all the open road heat out
Thats normal
The other is over filling the raditor, again usually after a run, and spews the access water all over the ground... dont over fill the radiator....both of these can be and often are combined.

A not on temp guns...most people dont read the instructions, assume that simply aiming at a particular surface will give correct reading... this in NOT the case... cant beat a good old fashioned bi metalic probe or a bit of mercury.
 
#10 ·
Just remembering when my 68 firebird 400 had overheating issues. If I remember correctly the thermometer was stuck open and when sitting in lineups the engine would heat up something terrible. Changed the stat and that solved part of the problem. New upper and lower hoses installed, then tuned up the engine and had the rad flushed.
It was an automatic and I believe I added a transmission cooler to reduce the load on the radiator

The firebird came off the road shortly after and it turned out the block was cracked. I have since rebuilt the 400 but am right in the middle of body panel replacement so cannot confirm that the problem is solved.
 
#11 ·
I dont see in your typing that you have the original shroud? If not, that is the problem. Shroud is VERY important. If you do have the shroud, is the fan blade sticking inside the shroud about an inch?
 
#12 ·
I would concur about the shroud and the distance of the fan inside the shroud.

The member with the Be Cool radiator and electric fan. I had the same set up in my '71RS (sold) and I too encountered an overheating problem in still traffic. As it turns out, in the Be Cool setup, there is about 1/4" to a 1/2" gap between the electric fan shroud and the radiator fins. I had a shop cut out an aluminum sided frame to seal the gap b/t the electric fan shroud with the radiator fins. This allowed the electric fans to suck up air through the fins, vs. sucking air between the fan/radiator fin gap. It ran much cooler after that.
 
#13 ·
I had cooling issues forever on my '69 with ZZ4 350 here in south MS. I have vintage air and would over heat sitting in traffic. I went with Alumitech rad and Spal 16" fan they also sell with the digital Spal fan controler and I never over heat even in South MS heat with the A/C on! It works great. Cost a little bit but I tried to go cheap at first and didn't work. i had him weld an extra temp bung in the hot side of the rad tank for the controller too for free.

This rad and fan:
https://secure.wf-api.com/www.cheve...-69-a-big-block-l-p-with-spal-16-fan-fit.html

This controler:
http://www.spalusa.com/store/Main.aspx?html=pwmv3
 
#33 ·
#15 ·
I had a 69 with a 396 in it as well. I too had the same problem. I put a new Harrison four core rad , new high flow waterpump , high flow thermostat, and a flex fan and a new electric Autometer temp gauge on my car and some of the Red line cooler in it too. The car ran around 210 and at lights got up near 230 . Drove me crazy. I use to work at a auto machine shop, and had seen many cracked heads and blocks. Pulld mine down, hot tanked them and pressure tested them with a blue dye and found nothing. Spoke with some old school guys and they told me some big blocks just run hot. I had a 454 in the car before and it ran 210 all day. The car still ran hot the day I sold it, still baffles me. I now have a 69 with a 302 runs around 190-200 with a clutch fan. I still have a hard time believing " some just run hot" sounds crazy to me. I wish you luck and please let us know what fixes it if any.
 
#16 ·
OK my radiator cap says RC 15. Is that ok? The shroud looks stock to me and the fan seems to be half way in and out. After reading an article link on here I noticed my hot air being pulled from the radiator really has no where to go when sitting in traffic due to the hood insulation and no venting so I can see why it's hot in there. Is there an easy way for me to test my clutch fan. I am getting conflicting results in research as to whether a flex fan will work.
 

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#17 ·
15lb cap is good...old caps are a common cause of hot idle...
Basic check for your clutch is gab the fan and check for any side play, and spins without a 'rumble' Careful on the play, that could be in the wate pump end bearing , dontconfuse the 2.
Im not familar with your shroud option.. even so Im questioning if u have the correct shroud....fan shoul be a little deeper in and maybe more room for air to move thu the whole radiator???

U meantion "new" radiatator(?) is it new or has just been seriously back flushed...
Flushing clears out scale build up, it DOEsNT unblock cores... radiator header are pulled off, and a trans oil dip tube used to clear all the cores.
If u remove the drain plug, use a bit of mig wire, hook out the crap in there....
lot of crap... chances are blocked cores...in effect 1/2 a radiator.
If u fire up 1st thing in the morning, as it warms up, the thermostat opens, wipe your hand over the raditor (grill side of caorse) it should heat uniformly...if it doesnt indicates blocked cores...they are usually lower in the radiator.

Dont go down the flex fan route...
I said before.. damn near all the 'old ' experianced guys here say the same...the orginal system is way over built, works better than any aftermarket stuff.
replacing with a flex fan doesnt solve a issue.

When ever a is brought into the work shop running hot or idle hot..
Routine checks
Pressure test system... pressure leak , runs hot
COx/ HC gas check of the raditor ... checks for blown head gasket issues
Check timing and fuel mixtures (O2 and COx)...the factory system on the 1st gen , being over built, these have to be so far out the car is going to run like crap anyway.
Replace thermostat and radiator cap
Back flush...
Failing that radiator goes to the radiator shop for cores to be cleaned.

Have u replaced and checked the thermostat and cap yet?... easy low budget stuff.
Get a HC. COx check... easy most workshops do this for free, take 5 mins at the most.. like a battery check, or tyre pressures.
 
#38 ·
I read the first half of this thread, in your initial post you wrote that it cools when driving but it gets hot in traffic. If that is the case, andyou have the appropriate shroud, I would look into the clutch fan. You could try a 'flex fan' as they are cheap and the ones I have seen and used had no clutch. If you do this just make sure you get the fan so it is about an inch inside of the shroud.

Has the block been bored? If so, how much?
 
#20 ·
Get the raditor checked for hydrocarbons/ carbon oxide compounds 1st...as suggested above... do it while out getting a new cap and thermostat...
eilimiate head gasket.
pull the stop **** and check in there for crap digging with a wire...
Give the radiator a though back flush....I drop the coolant, fill with water, mix up a 1/2 cup of washing machine powder in a bowl hot water . pour that in and go for a good 10 mile drive....the drain and back flush everything till no more bubbles in the water.
Back flush... thats water in the bottom of the radiator, out the top....in the top of the engine out the bottom.

Before pulling stuff apart

And follow up the shroud... it doesnt look right to me....too close to radiator and fan not deep enough in.
 
#21 ·
Can't tell from here, but shroud looks like the factory type with a long waterpump. Mine was pretty shallow as well , and it was GM. Any shance the clutch fan is not locking up? If it is free wheeling it is poss this is your problem. Clutch is not very much money and not too hard of a fix.
 
#22 ·
The clutch wont lock up but, at or above operating temp it should have some resistance. Get your engine hot and then shut it off and check.
when cold, it should have the slightest resistance but not quite free wheeling.
That would be a sweet fix if it was the clutch, like you said it's relatively inexpensive and not too hard to change.

Also, I think for maximum efficiency, the fan blades should be approximately 2/3 inside the shroud.
 
#23 ·
the fan blades should be approximately 2/3 inside the shroud.
yes....if not peek spliiage is off the very tips, if those are outside it just caviates air, rather than moves it thru the raditor at idle...
Then once the car gets up arond 20 mph there is more air than any fan could move and issue goes away..
Like I said above, im not familar with that combo raditor/ fan/ shroud, but it looks and sits wrong for the application.

Just thinking out aloud here...if a stiff cardboard strip was made up to to go aroud the shroud.... in effect put the fan further into the shroud, and held in place temporaly with duct tape, and see if that makes a difference?????
 
#24 ·
I could be wrong, but I thought that the shroud was for lack of better terms a funnel . Correct me if I'm wrong, but doesn't the fan pull the air through the rad and the shroud funnels it around the engine to cool it? It is also poss that for some reason a cerpinteen fan got it's way on the car, and the blades would push instead of pull. Just thinking out loud without looking at the correct fan I get confused on witch one pulls and witch one pushes. I do agree that the fan should be in the shroud, but his shroud looks to be correct. Small block shroud wont fit " too deep and not off set". Would be nice if a big block owner could post the size of their shroud so that he could compare to his.
 
#25 ·
Correct me if I'm wrong, but doesn't the fan pull the air through the rad and the shroud funnels it around the engine to cool it?
No u are not wrong....

That is the function of the shroud 'housing' ....what is of more concern here is the shroud function to increase efficiency of thefan by stopping spilage of air off the ends of the blades
A great example of this is our computer case fans...if they did not have the outside surround on them , they would need to be nearly double the size and pull 2x the power draw.......A jet engine impeller another example, be it a plane or hamilton jet boat.
And of coarse the electric radiator fans....which unlike the hugely efficient GM fan and shroud that draws air thru the whole raditor, only does so in the area of the diameter of the fan.
 
#26 ·
Good on the fan shroud and clutch. Rad cap may need to go to 18 lb to prevent boiling when shut down after a drive.

Since the picture shows BBC w/A/C, BBC's came with panels between the radiator support and inner fenders, good luck in finding them, but they do show up occasionally, and have a 1 inch thick foam gasket across the top of the radiator support.

These devices prevent recycling the same air through the radiator. The air will escape through the engine compartment, but some gets recycled, the less, the better. Also, an idle-up solenoid for the throttle to kick it open alittle when the compressor kicks in.

A good fan pitch (angle of the blade), clutch fan, clean condensor/radiator fins, and stopping an extra 3 feet behind the vehicle in front of you, helps.
 
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