Put a resistor in the line.

You can buy a variable resistor from one of the Corvette part suppliers for this purpose.

I needed a 37 ohm resistor (IIRC) to get my gauge to read right, I just did a trial and error thing with the resistors until the 180 coolant temp matched the gauge reading: 25 ohms was too hot, 75 ohms read too cool, 50 ohms was better but still too cold, etc.

Doug

 

Originally Posted by 67Elkhart View Post
Anyone know where to get a sending unit that works accurately with the old gauge?


Mary Jo sells old original Delco senders for C-1s. I believe they are the same calibration for C-2s.

www.vettegal.com

 

The conversation is all over the map which is good.

In a prior post we learned that a 25ohm sending unit would register 180 degrees. In my case the IR gun and my temp gauge are speaking the same langauge.

The IR gun also read 240 degrees and my gauge said the same, along with the car puking, verifing what was going.

It came down to the car not getting enough air due to a fan system that was not working as advertised.

Dennis

 

I was having an overheating problem that I could not figure out for a long time. Just about everytime I shut the engine off after running the car after going for a cruise the car puked antifreeze out on the ground. I thought I had too much antifreeze in the car but I was dead wrong. It always ran cool when driving it but when in slow traffic the temp went up or if left idling for a while in hot weather the same thing. Believe it or not I corrected my problem by just replacing the Radiator Cap with a brand new one. I even changed thermostats pryor in my quest for a solution which didn't help any and checked everything from timing to whatever I could think of. Never thought to try changing the Radiator Cap out since the one on the car looked to be a good Radiator cap. Boy was I wrong to think that. It was a very cheap fix for me after a lengthly time of not knowing what to do with my problem that I even mentioned it on this forum a few times while seeing what others were doing with their overheating problems.

 

I purchased a new sending unit (for my new zz454 engine) from Advance Auto Parts. My temp gauge reads dead-on with the IR gun.
Roy

 

This just happened to my brother inlaw. He purchased my old 55 that ran cool with stock setup. He had the car rewired and aluminum radiator installed the guy that did it told him to run electric. the car overheated after he got it back. Trouble shooting I found the fans were running backwards.

 

Absolutely! GM used flex fans on many vehicles in the 70's (and probably the 80's as well) that I know of. Most big engined, big vehicles with AC had the flex fans. Big Pontiacs were a favorite due to the size that matched the vehicles/fans we were replacing them with. I was Pres. of the local Avanti club, and we found that the Avanti II (with SBC engine) needed the flex fan, rather than the clutch version the Avanti factory was using (especially on the 400 CID engines used during the early 70's). I helped several members changed over to the flex fan, and the problems disappeared. We raided the local junk yards on several occasions for them. Also used the flex fans on several other vehicles where they always helped.

Plasticman

 

Seems like a lot of people do not like electric fans. Maybe I have been lucky with the one I installed but I do not think I will ever go back to an engine driven fan. On my 1975 Corvette that I drive everywhere, Orlando to Jacksonville, Jacksonville to Sarasota etc. I have an electric fan as a primary means of cooling and it has not once overheated. One thing different from other people's electric fan swaps versus mine is I did not use an aftermarket fan. The fan I used came off a front wheel drive Mercury, early 1990's vintage. Mercury version of the Ford Taurus, I think a Sable? I laughed when my friend recommended it to me until I took a look at it. I pulled the entire assembly out of a car at a junkyard. The fan assembly comes with it's own shroud, and has two speeds. I used a $20.00 thermostat control from Advanced Discount Auto, on at 180 off at 160. I have had the car on the road for over a year, not once has it over heated. Car stays cool and the fan only really comes on when in traffic on a very hot day. In Orlando on I-4 that can happen pretty frequently. Even in the Florida heat it only takes the car about 5 minutes to cool back down to 160 and the fans to shut off. Like I said maybe I am just really lucky this set up works for me. On the highway the fans don't even come on, but that is also most likely due to the fact that the shroud does not cover the entire surface of the radiator and lets air flow through at highway speed. Does the shroud you had installed on your car have one way rubber flaps installed on it? I have seen some aftermarket fan assemblies with shrouds have this feature. It allows air to flow through at highway speed but while stationary at idle the vacuum created in the shroud pulls the flaps shut. Just another point of view

 

Are you using the original distributor with vacuum advance?

 

I've been following very closely all the vicissitudes of overheating woes
in this forum and there seems to be many different solutions. I had my own problems as well with my '66 BB a/c car. I had my radiator reamed and boiled out, changed to a correct sending unit, changed the fan clutch, went to a 7-blade fan, on and on, etc. but along the way two things worked best for me. First, a correct sending unit supplied by Paragon that gave me a more accurate reading. Instead of topping out at 240 degrees it was corrected to 220 degrees but obviously it was still too hot. The other change made the most difference. I had overlooked a missing lower fan shroud extension! IMO, a BB a/c car has
a condenser in front of the radiator that impedes cooling from air going through the grille and that the lower extension for the shroud made a world of difference. My well tuned car now runs 190 degrees max on the freeway with the air on. I do avoid driving with the a/c on in stop and go traffic in 100 degree plus weather because in my last experience I saw the needle climb to almost 210 degrees. My story just goes to show that there isn't always just any single cure for overheating but that it can be a combination of many factors. For me it had to be the shroud and a trustworthy gauge, and likely the addition of a 7-blade fan.

 

The factory fan and shroud system may cost power to the rear wheels, but it is also the system that has the power available to drive a fan that can overcome the pressure limitations of the cooling system radiator core.

I am very please to read the cooling problem is solved.

If anyone does choose to go electric, the Lincoln Mk8 or Taurus/Sable fans will flow air and pull the static pressure needed for the thick core radiators. If you use these fans just be careful with the wiring, and use wire that is as thick as the factory system or larger that can handle the amp draw and wattage (or use a controller that limits the amp draw on start-up).

 

Why would you worry about 210* in traffic on a 100* day with the a/c on? That ain't bad in 100* temp outside.

 

Thanks -

Mark

 

The problem is not likely with the fan, but that it was running while you were going 70 mph. At that speed, the fan will only act as an obstruction to the huge amounts of air being pushed through the radiator.

Factory electric fans do not run once the car is moving approx. 30 mph or more. With or without a/c, the air flow from the moving vehicle is greater than any fan can move.

 

hamilton, I started this post and I as I said earlier I came to the same conclusion that you did, however,you did a better job in describing the the air flow or lack of it do to the elect. fan running at highway speed.

I was not aware that factory installed elect. fans cut off at highway speeds. If this is correct and in my case I believe what you have stated in more than likely what I was experiencing. I wonder why this product was not set to operate in this manner.

I had direct discussions with the experts in this field, and the Mfg. of this product with not a suggestion that this is what might be going on.
In fact it was mentioned that a larger radiator might be the answere.

I went out of the box to a shop that builds Baha racing trucks because I had been watching a tv show when they discussed heating problems they incur in Mexico. Bingo I was on to something and I acted on it.

Guess what guys, I was the only Corvette in this shop for trucks heading for Mexico, go figure.

My cure is not that unique as a number of you had other issues which were solved with the obvious remedies. All I can offer is that a few of you spoke of the fan situation, I failed to do anything about this until the last because I had what one would have thought was the best product enginered for a Corvette.
Dennis

 

So where did you get the flex fan and the spacers? Is it something like this?
http://www.jegs.com/webapp/wcs/store...10002_13940_-1

And you removed the clutch correct?

 

Ah, okay, I see what you're saying now I wasn't sure from your 1st post if you had tried running on the highway with the fan switched off... sounded like it continued to run. I didn't see your earlier posts on overheating, don't get time to stop in the forum too often. But, as you found, the engine fan is probably the best option.

I don't know what the electric fan setup looked like, but if it had a shroud covering the face of the radiator, that would also have hurt air flow. All the factory electric fans I've seen have no shrouds. I assume they pull enough air at idle to make them unnecessary, and also because they're right against the radiator its not needed. Not like a mech fan which sits far from the rad (and those big shrouds would not obstruct the air flow).

I can't imagine why manufacturers do not know that the fans should shut off at speed. Of course the OE setups have the Vss and PCM, so shutting the fans off at speed is trivial. I expect it would be too complex for aftermarket fans to rely on a speed sensor or air flow sensor. Maybe they expect the rad temp (assuming one of those radiator temp sensors) to drop with high air flows, and that shuts the fan off? But as you discovered, it won't cool the radiator if it's blocking all the air.

-Michael

PS: I'm glad I found out about these electric fans before I went and bought one. I wanted to replace the direct-drive metal fan my father put on the '60 years ago, but now I think I'll look at a stock clutch fan or just leave the fan alone.

 

"My cure is not that unique as a number of you had other issues which were solved with the obvious remedies. All I can offer is that a few of you spoke of the fan situation, I failed to do anything about this until the last because I had what one would have thought was the best product enginered for a Corvette."
Dennis


It's been stated many times that if you're having cooling problems on your Corvette, make sure the cooling system is to the original engineering specs and you likely won't have a problem. You are close but no cigar as your Corvette did not come with a flex fan when new. I'm not saying it's not effective though.

Now, somebody tell me what the difference is between a flex fan whirling around on the end of your water pump and blocking the flow of air at speed and an electric fan running full time doing the same thing?

The factory installed electric fans I'm familiar with turn off/on as directed by the engine coolant temerature sensor, not road speed. But, I'm certainly not familiar with all of them.

PS. I ran my '63 ALL LAST SUMMER in heat as high as 100* with no fan. That's right, no flex fan, no fixed fan or no clutch fan. Ran right on 180. That's what the thermostat is rated at.

I use twin electric C-6 fans with a shroud to cool the LT-1 engine in my Corvair. The engine is in the middle and the radiator is in the back. There is no forced air a highway speeds, only what the fans push through the radiator.

The above is what prompted my initial comment that somebody(?) wired your fans up to run backwards and I still think that. Sorry if you find that offensive.

 

I found an old post from may of 2005 of mine... I was having serious problems driving in traffic Grand Central Parkway... spoke to tom dewitt and he figured out a product for me that works well with my 327 bored .60... the flex is still on but hidden in front of it is an electric attached to one of tom's radiators..both pulling when the engine hits 195 and the electric suts off automatically at 175..

here is what I posted in 2005 .. three hot summers later still no problems.. and the Grand Central does not have any less cars in traffic then it did 3 summers ago



Hot weather is on the way and we are going to get the usual "my 327 is running hot threads".. timing will always be the first discussed "did you check the timing".. then we will get the thermostat issues..160 vs 180.. then water wetter usually gets mentioned and dismissed by most..vacuum advance is usually mentioned as being hooked up at manifold ( that helps a bit)... .. then we get to the radiator..

Have a 1960 with a nom 327 bored .060 have in past done timing,water wetter..stewarts hi-flow water pump.. 160 therm and 180 therm .. drilled small holes in them..etc etc.. always above 210 in traffic and climbing fast.. was scared to take my car to work in the summer everday as worried about killer traffic here in Long Island

Last year went and bought a dewitts radiator..with an electric fan (on at 195 off at 170..still using the stock fan in addition both pulling

Dewitts made a great bolt in product. and I had a chance to REALLY test their product..no not in the desert..as that's no real test as you are moving.. but in a real world test.. the Grand Central Parkway On Friday at 5:00pm
those not familair with the GCP should picture the slowest moving highway they can imagine ..where it takes 90 minutes in stop and go traffic almost every Friday in the summer to go 17 miles.. The other day when the temp went up to 72 I decided to be the GCP tester with my 4.11's.. long story long.. Going to Queens no problem with traffic.. coming home.. 90 minutes stop and go for the entire 17 miles..dewitts held up great never went above 185..fan never went on. was not even nervous just enjoying the sun.. listening to tunes.. and glad I did not take the station wagon to work that day..and plan on not taking the wagon much this summer

not saying that timing can not solve a lot of problems but for the drivers out there that have tried everything else.think replacement.. I am very happy with the product.. people at dewitts easy to work with as well

 

I'm not an expert in fluid dynamics, but I expect it has to do with the electric fan being right on the face of the rad, verses the mech fan 6-8 inches back. The engine driven fans have much larger spaces between the blades, in addition to turning slower than an electric fan.

I do not recall where I learned that OE electrics shut off at road speed, but I can find out. However, I am 100% sure that the fan is unnecessary at any speed over 30 mph, as the air flow of the moving car is greater than any fan.

I have an LT1 '96 Impala, the dual fans have no shrouds. All the passenger cars I've seen have no shrouding on the fans. Not saying that some didn't come with shrouds, but *most* have no need for shrouds with the fan right on the rad. Seems to me a shroud right on the face of the rad would seriously block air flow. Then, your Corvair is not trying to force the wind through the radiator.