I have a 1968 with a 350 and a 4-speed. At idle the tempature creeps up to 200 to 220. I can't get the tempature to drop by increasing RPM. As soon as I start driving the tempature begins to drop. The radiator coolant has been changed and is clean of rust. The previous owner installed a flex fan and claimed that the radiator had been professionally cleaned. Where should I start?

Hi David, and welcome.
Try doing a searh on your topic...you'll find TONS of info. Way too many questions to ask to help:
Fan shroud?
Timing?
Thermostat? etc, etc.
See what I mean?

1st off I have had the same problem and have been doing things to my car for the last 2 years, my car could overheat with the a/c on when I would sit at a light so I feel your pain and hopefully I can help you threw this… do you have a shroud on the car? what size radiator do you have... 3 core 4 core original or the new kind with high efficiency fins, copper or alum... I have an over flow bottle and a 2 core alum on my car, if you can go alum it’s the BEST way to go and I guarantee it will probably fix your problem!!! but back to things you might do, over flow bottle that does is allow the radiator to run with the maximum amount of coolant in it. You might want to check your coolant to water ratio, the more water you have the better, I have a 80% h20 to 20% anti freeze (b/c water is a better heat dissipater) you might want to check your timing b/c my car was running 'retarded' at 10 tdbc so I moved the timing up to 25 at idle and did away with the vacuum advance, you want to make sure of this b/c if your timing if off at idle... which you said your having your over heating problem its cause premature igniting of the fuel thus making hot hot exhaust and your exhaust ports are by your coolant ports that run through the block thus increase heat. You might want to check your water pump, the stock one wont cut it you need a hi efficiency one that really puts the water through your radiator. Another thing is I have a elec fan mounted the radiator that pulls 2,300 cfm at idle plus my mech. fan so that really does the trick you really need to make sure you have a sufficient about of 'cfm's' being pulled through your radiator at low rpms... hopefully this will help

oh yes read this also JohnZ gave me this excellent reminder..

JohnZ
Tech Team


posted 03-26-2004 06:53 PM
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How is your vacuum advance set up, and is it working? If it's connected to "ported" vacuum, as most of the "smog" engines were, you have zero vacuum advance at idle, and it'll run HOT at idle and in traffic due to retarded idle spark timing and VERY high exhaust gas temperature, which gets transferred through the exhaust port walls into the coolant. First thing I'd do is 1)Make sure it's working, and 2) Connect it to full manifold vacuum so it adds about 15 degrees at idle. Inoperative or "ported" spark-connected vacuum advance is responsible for LOTS of idle/traffic heating problems, and can cause heating issues on the highway as well due to inadequate advance at cruise load. If that checks out, you either have an inadequate airflow situation at idle, wrong shroud, seals missing, or not enough radiator (in that order).

Also, and I know this is really basic, but make sure the fan is pulling thru the radiator and not pushing. One guy I know had this problem. Make sure your T-stat is working correctly. You didn't say whether you were losing coolant thru the overflow or not. Check your pressure cap. Run about 15 lbs. Check your coolant when its cool. If you are not using an overflow system, make sure your coolant level is at least 2" from full up-to leave room for expansion. If you are using a coolant return-fill 'er up. How do you know you're even running those temps? Are you relying on your gauge, are you getting a correct reading?
Sending unit and wiring OK? Where is your sender located? In the head? See, it could be just one simple thing, or an entire menu of stuff!
But please read thru the posts. Thats why we spend so much time trying to be as thorough as possible. I'm sure the answer is already here somewhere! And please post your results...you know, for the next guy with the same problem.

Just for the record, and to give a slightly different approach, I have a 68 with a new 385 Fastburn with HOT cam and 1.6 r/r's (about 425 hp) and I live in Los Angeles where it can get kinda toasty. I'm using the original radiator that came with the car when it had a 327 in it. I'm running a straight fan, no clutch, no flex, 6 blades. Original fan shroud. A 1" spacer to put the fan half way in the shroud. My motor came with a waterpump, standard GM stuff. Nothing exotic at all. And I haven't been over 190* yet. I'm using a coolant return tank. I have a temp gauge, a small thermometer at the radiator and an I.R. gun so I can get a "relative average" of what my temp is.
Before the new motor, I had an old 70's low-comp, big cam, kluged together, junk headed, contact points, no vacuum, no h.p. 350 that, for a number of reasons, was better used as a boat anchor. It overheated ALL THE TIME. Couldn't keep that thing tuned properly. And I had the same cooling gear I have now!
If I do discover later this summer that Im starting to heat up, then maybe I'll switch to an aluminum radiator. But that's it.
JMHO, as always.

Good luck!

Originally posted by David A:
I have a 1968 with a 350 and a 4-speed. At idle the tempature creeps up to 200 to 220. I can't get the tempature to drop by increasing RPM. As soon as I start driving the tempature begins to drop. The radiator coolant has been changed and is clean of rust. The previous owner installed a flex fan and claimed that the radiator had been professionally cleaned. Where should I start? Classic signs of not enough air flow through the rad core. If it were timing then sitting still and increasing the engine speed would advance the timing, cool thing down. Once the car is moving you are getting the air you need through the core and the temps come down. A good shroud and a fixed blade fan (clutch or not) will most likely be the most ecominical solution.

Thanks for all the info. I covered most of the bases before posting but apparently not all. The vacuum advance was disconected because a HEI distributor of an unknown year replaced the stock one. It was pulling nearly 40 degrees at an idle. Since I don't have the equipment to adjust it, it has been on my to do list. I have a mechanical tempature gauge with the sender in the intake manifold. Should I put it in the head? Lastly I don't know about the water pump. I suspect it is stock and not a high flow. I will start with the timing and go from there. I will let you know what fixes it.

David - As I said above it doesn't sound like timing!! Running retarded is what causes overheating. You may have timing issues but it's not causing your over heating!! You have an air flow through the radiator problem...

Point taken. I'll start with a fixed fan.

I replaced the flex fan with the stock fixed fan. The tempature still creeps up when the car is sitting still. When I bring the engine to 1500 rpm for several minutes the tempature stabalizes but doesn't decrease. If the car is moving the tempature starts to drop. What's next?

If the stock fixed fan is only a 4 blade, that may not do the trick.

Look for one with more blades (6 or 7) and try again. Like DJD says, try the cheap fixes first.

Ok, lets take it one at a time:
Fan Shroud:
1. Do you have a shroud?
2. Is your fan about 1/2 way in the shroud?
3. Is your fan pulling a good volume of air thru?
4. Is the shroud in good shape all the way around?

Yes to all. I'm going to pull the thermostat today just for the off chance that it is restricting water flow.

This is the classical airflow at idle problem. YOur raditor will cool as soon as you get rolling indicating airflow issues. You either have to increase airflow at idle or get a more efficient radiator?

The easiest and BEST upgrade you can make to your existing set-up is dump the fixed fan for the Derale Heavy Duty Flex series 17XXX part number only product. This product will take MUCH less hp than the fixed product, and provide probably 50 to 100% more airflow. This flex fan series is a high quality, designed for 8000rpms, and provides "entrapment" technology for keeping the blades on just like the stock one. Plus, it's high quality "progressive formed" stainless which acts agressively at low rpms, but gives up the ghost on higher rpms. It's also quiet. It's the best product out there for about $55 from Summit Racing. Go to http://www.derale.com/flexfans.shtml for more information. I have recommended this fan hundreds of times without a complaint!

I use this on my 400+hp Camaro ragtop here in Hotlanta with air.....and it never comes off the 180 degree thermostat cycling point. The fan moves about 15% more air than a big block/clutched models FWIW. I am using the 17" with a stock shroud but the 18" will go in too.

Try it...for roughly $60 you won't believe the difference.

ps......taking your thermostat out may hurt you more than anything else unless it's not working properly. I would get the Mr. Gasket "high flow" balanced thermostat from Summit to run. These will NOT stick closed and are quality products.

For more cooling info....go here http://www.oldcarsonly.com/page/page/776256.htm

Hi,
I experience the same problem as David on my camaro. I am running ported vaccum advance because the car start easely that way. I think i need to remove advance if i were running full manifold vacuum advance. When i plug it there at idle the engine almost stalls!
Do you think i should try to run manifold vacuum and re-tune my advance? by the ears because i have no lamps to halp me do it.

I have a stock coolong system, stock shroud, fan and radiator and a good water pump. HOTRODSRJ, this modern fan interest me, because it might be the solution.
Is it a thermo-clutch fan?

I guess when we speak about flex and fixed fan it means that the fan motion varies with the RPMs?

I don't know what fan i have in my car. I have a small radiator i think maybe 1 or 2 cores.

Please tell me about flex and fixed fan differencies and the possibility of adding a thermo-clutch on my car?
Also i will add a spacer to move the fan frontward because i know it is not inside the shroud.

Thank for your input guys.

Marc

My car isn't home.
If i want to select a fan, i need to know the rotating size . Is it clockwise on GM V8's?

Marc.......when we talk about flex fans, usually if not all the time they are non-clutched mechanical fans that make the blades flatten out somewhat at higher rpms to reduce the blades "bite" thru the air...assuming higher speeds which you don't really need a fan with.

Older style flex fans have dubious reputations for coming apart and exiting thru you hood and/or not being very effective for cooling. All these reasons were and still are valid with certain models and manufacturers. And never put a flex fan on with aluminum blades period!

I am not a "clutch regulated" fan (pun intended) per se. The reason is that you NEVER know when they are 100% working until you have problems. And, on top that the aftermarket produces rough "universal" replacements for specifications of yesteryears that were many based on many diffent issues. GM made over 50+ specifications (air, big block, heavy duty cooling, towing, truck use, hp variations of the engines, etc) of these clutch fans in the 60s, 70s and 80s. What happens is that these "universal" models do not fit your application necessarily and can leave you with underperforming fan system. Some are very successful in utilizing these tho, but it's a guess in my opinion even with direct replacements from some of the more so-called quality suppliers.

The new fangled Derale heavy duty flex series is a direct mounted mechanical unit and will outperform the best clutch models. YOu definitely need to put a 2" spacer on to get the fan at least 1/2 to 2/3 the way inside the shroud. This is important.

On the vacuum advance front, yes...run full manifold vacuum. I don't understand your starting problem per se with the supposed full time vacuum? When you plug into the manifold vacuum source you will induce more timing to the idle equation. This should increase your rpms and you will probably have to reset the mechanical idle. MOre timing at idle will smooth out your idle and help with cooling as well. It also gives better "tip-in" throttle response.

David A,
Time for an update....whats going on with your car?

And David, did you solve your problems then?

FOr my part, i want to ask you if the new fan will really be the solution as my radiator is a 2 core one ?

Maybe i need a bigger radiator.

And where i live, i can't try smth and then try something else because of the shipping.

Marc

Believe it or not I'm still working on it. Yesterday I pulled the radiator and had a local shop go thru it. It helped a bit but didn't solve the problem. I have tried everything else except for an electric fan and an aluminum radiator. The one possiblity I haven't covered is the water pump. A mechanic said that since the radiator is the same temp as the tempature gauge the pump is working ok. Otherwise the radiator would be cooler than the engine tempature due to a decreased flow. I noticed today however that with the cap off I could not see any movement of the coolant after the thermostat opened. In other cars I have seen the coolent move across the radiator after the thermostat opened. Tomorrow morning I am going to have the water pump flow checked and then go from there.

summit sells a high flow water pump,
that along with the high flow t/stat helps a ton.

It helped my big block,a bit,and when i put the griffin alum H/D radiator in,then i had No more
cooling issues.
I never reinstalled the pusher electric fan i used to help with traffic jam problems.

graemlins/beers.gif

Take a peek at this thread:

Cooling system considerations (http://www.camaros.net/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic;f=19;t=000309)

It may provide some direction to the selection of parts that have worked in similiar applications to yours.