If you do in fact find out it's the tstat that is bad, go for the fail safe variety as a replacement.. it's cheap insurance! I still would do away with the aux fan and the flex fan and go to a clutch fan..and a new rad... When I was dealing with the heat issues, i started out with the clutch.. it helped, but it was still too warm. I went for the tstat.. put a 160 in it and still was gettin over temp.. I finally changed the rad and all the issues went away!

 

Right now I'm using the "correct for stock" temperature thermostat. My motor isn't original, so I don't know why I did that. I think I'm running a 190 degree thermostat.

I'd like to step down in temp, any suggestions on temp? Is 160 too low?

 

180-195 is fine

 

Just throwing an idea out. Do you have the factory front spoiler on your car? If your missing it that could be a problem as well since our cars are bottom feeders.

 

Check the Dr. Rebuild catalog for the seal to use between the fan shroud and the hood. There is good information there on which year to order if you have one of the later sharks (with cold air feed on top of radiator) and you have removed it. I think you order the seal for the 73, but the catalog has the details.

 

That was a huge problem on my old 82 TA. It was a total bottom feeder and I broke 2 chin spoilers off in our winters. It actually made about a 40 degree difference at speed in my car. If your problem is at idle, the chin spoiler won't matter at all.

 

I do have the chin spoiler. Tonight I replaced the thermostat with a 180 degree unit, put a new radiator cap on it (one without the latch) and wired the switch to the elec fan. If left on the elec fan does have a small effect on the cooling of the car.

Now I'm just waiting for the seals to get here. But I don't think they are going to work. I don't have the air box that sits on top of the radiator. I wish I had thought of that before ordering them.

 

Mine is down to either a finally worn out iron FlowKoolr highvolume or, yet again, a blown head gasket. It was running fine and hard (for a change). Right before an evening cruise I checked the cooling system and saw my overflow tank was overloaded and the radiator was down a little. which was odd. I immediately blamed the radiator cap on the water neck blocking the return of fluid from the overflow tank and so "addressed" it by butchering that seal a little.

Fifteen minutes later I just had to shut it down when the temp passed 290. I let it cool, used all my on board water, limped into the next gas station, cooled and flushed it all and got home without it even heating up hardly at all. I suspected the wp had finally gone out, but realized it also could have been the cap I suspected so got a 16# cap for the radiator and a 7# cap for the water neck filler, a bottle of Purple Ice wetter agent and two gallons of Sierra. (As well as having to shoot two cats who got to regular AF, I seem to be harshly allergic to ethylene glycol - so I use the propylene glycol less efficient stuff in all vehicles.)

I saw the pump was pumping forcefully enough at idle after I changed everything. Well, that did little and I had to shut it down AGAIN. My hope is my sudden new problem which only occurs after a higher speed run and seems to do nothing at lower is the water pump is getting erratic. It's due in tomorrow and I hope that simple swap will take care of the new problem and I can get back to the puppy just running a little warm with the new engine and the even still cooler temps.

I've altered a lot of the cooling system and expected two more major thrusts before the next engine change when I will get the absolute highest rated aluminum radiator then available.

I bought an auxilliary electric fan like yours - which is where I intend to mount it. I will probably do that when I put in the new pump. That is mainly for slow moving with no air scoop effect.

I do not agree with the earlier poster than that fan will negatively affect your mechanical fan and you should do one or the other. I intend to use both (at least for now) and most of the uses of electric fans when I was in vehicles earlier were as an auxilliary to the mechanical and frequently the only place to mount them was behind the radiator. I do agree with the other poster to have the fan on all the time unless you have electrical issues.

Of course both fans should pull through the radiator towards the engine.

I don't agree with the use of a fan clutch when you do not have one. I took them off of every vehicle I ever owned with them and replaced them with flex fans. They ARE useful and save some power when not needed, but I feel add an unreliable component.

My system is a little different and I should mention those differences so you can see what may or may not be similar.

As mentioned I currently have a high flow FlowKoolr iron wp which will shortly be a high flow Edelbrock Victor aluminum pump. I have a five core copper radiator and solid SS main radiator hoses. I have an elevated water neck with a primary fill location on the waterneck. I do not use a thermostat at all, but rather a flow restrictor orifice plate. I have above Edelbrock RPM AirFlow intake fore-to-aft coolant runners to connect front and rear head water passages as an easier alternate to a rear Y-pipe modification. My engine is a 400 block so the head gaskets have additional vent holes drilled to allow steam pockets to vent. I converted my A/C condenser to a monster tranny cooler, which has worked well. I also have an auxillary oil cooler in front of that. I have water temp, oil temp, tranny temp and diff temp gauges with new senders. My A/F ratio is decent - not too lean. My timing is decent, not too far advanced nor extremely retarded - the two main engine conditions which will elevate temps.

I do not have the heater core blocked off at all, but do have a new heater core and two manual valves to cut down and shut off the heater flow as I wish.

I added about three inches to my somewhat damaged fan shroud with a formed peice of 3/8" lexan. I spent a lot of effort replacing all the factory radiator area gaskets and adding additional expansive foam to plug all other air flow gaps. I recently have worked on my chin scoop thing because it had always been damaged and actually restricted the air flow and was seeing some results from that over the last few weeks before this sudden thing cropped up.

Now assuming I do just have a weird wp malfunction, I intend to do a lot more work on the air scoop system and make a foam filler to minimize the gap between the shroud and the mechanical fan. As mentioned I intend to mount the electric fan, without a thermostatic control but I will put a manual switch in - possibly in the engine bay to be able to turn it off manually during colder times when I would open up the manual heater valves.

Some observations on yours come to mind immediately. As someone mentioned your thermostat may be malfunctioning. I would use the lowest temp, but as an 50-60% a/f mix boils at 250-270 with no pressure and as high as 290-300 with a massively overpressured 22 psi system (1.5 atmospheres), running at 195, 205 or even one degree below your actual BP of your mixture is fine. Your engine can run well and efficiently at 400 degrees, but it's not stable as that's way beyond where water boils. (Evan's waterless, almost pure propylene glycol coolant system is DESIGNED to run at 300-325 - I still want to talk to some people who have actually used that setup.) The problem is you heat up the system faster with a higher thermostat which is bad if you have a heating problem to start with.

Your thermostat may not so much be temperature sticking as being overpressured and forced closed. High flow thermostats avoid this, as does drilling a couple of 1/8" holes in the flange near the "working bits" as does using a restrictor plate (the mid sized one is usually right for SBC's, but this engine and water pump seems to like the larger opening.) Absolutely do not, ever, run an SBC without a thermostat, especially with nice high dollar aluminum heads. Some engines run cooler and better without a thermostat at all, but not SBC's. You need the restriction to keep the coolant level in the heads high enough to cool them uniformly.

Another thing that hits me is how did you block off your heater core? The safest way to avoid some wierd disruption in water flow through the starboard head is to short circuit the hose between that connection and the water pump. As regular heat control valves typically shut this circuit down the whole way, this wouldn't seem to be a problem, but I've never trusted that. Earlier I ran into a problem on my setup by opening my two valves all the way! This let too much flow through and starved one part of the system causing an overheat! Now I only open them a maximum of about 1/3rd. and never shut them all the way to keep a little flow through the heater core to prevent odd pressure backups and minimize corrosion. Remember, your heater core makes a dandy auxilliary cooler.

Your instincts on the shroud gaskets are dead on. You really need the seal especially at the top between the top of the radiator/subframe and the hood when closed. To make temporary repairs to get the thing running without changing all the involved components, use pieces of sheet metal, generic weatherstripping/gaskets and expanding crack filling foam.

Your symptoms are consistent with thermostat failure - and also not inconstistent with wp malfunction. They do not always squeal, grumble or leak out the seep hole. Good thought about putting the wire in the lower hose - I had forgotten about that and that CAN collapse. I assume you DID use a new wp...if not, try even a cheapy low flow parts house iron one for a little while - should be able to get one for $30-50.

Since you describe it heating up fairly quickly but not "explosivley" and not a gradual buildup that just never ends I really think this is water flow or the restriction thereof. A major head gasket problem will vent coolant quickly - literally boil and push it out of the system. A gradual buildup is not enough air flow.

One problem not mentioned a lot here is air pocketting in the top of the radiator. That's the whole reason I put on my waterneck filler thing from Moroso, especially since I have rigid hoses you can't "squish" to get the air out of. One other way to accomplish this is park the car on a severe incline with the right front as high as possible. From cold and unpressured, especially since you have a thermostat, run it with the cap off until the thermostat opens and then fill it - getting all the air out before sealing it. This is a lot easier filling with hot water (so you don't close the thermostat that just opened...) and actually doing it when the coolant is still warm, just not warm enough to be presurizing the system.

You COULD have an air pocket problem, but it doesn't seem enough to account for your level problem.

On the laser temperature deals - you can get those at Sears for $60 or even less for the lower range ones good enough for anything but exhaust.

Last observation - try seeing how fast the air seems to be moving in FRONT of the radiator, from underneath the car when it's running with the hood closed. Without one of those little windspeed meter thingies it's just by feel but I've never thought mine really moved enough. It should be very noticeable an inch or so off the fornt of the radiator.

Oh - my '75 doesn't really have an airbox on top of the radiator/subframe....just a raised portion of the subframe and the gasket that mates to the hood.

As soon as I get my pump on and see if that does it I'll repost - let us know what you come up with too.

 

You said you put in a new sender. I hope you didn't buy one from your local parts store (AutoZone, Advance, Etc.) If you did you have the wrong sender. I had the same problem. Check out Lectric Limited. com on the net. They will send you the correct sender for your application. Since I installed theirs my termperature stays right around 180 deg. Before with a sender from Pep Boys I was reading 220 and up.

 

My sender is from O'reilly Auto Parts. I just called Lectric Limited. They don't carry a sender for 1980 Corvettes. I looked through the online catalog and they don't carry a sending unit for anything past 1978. Anyone know the resistance for my particular year compared to a 1978?

Last night after changing the thermostat I left the radiator cap off. I started the car and waited for the thermostat to open. Right as the temp guage hit 220, the 180 degree thermostat opened and the radiator got low. I topped the radiator off and the put the cap back on. The temp guage stayed right at 220. I am pretty sure that the guage is reading around 40 degrees high. Anyone agree or disagree with that thought?

 

i've updated my site to include a test for cracked heads(see#4)
http://community.webtv.net/MATTGRU/doc

 

have u verified the sender with a pot of water yet?
appears to read 40 high?
One could remove the gauge needle and reset it to match

 

Matt,
I rigged up my sending unit and dropped it in a pot of boiling water.

This:


Produced this result:


So, is it safe to say that my guage is reading 40 degrees too high?

So, when my guage reads 220, I'm actually running at 180?

 

Most of all possibilities have been covered. You didn't say how the engine was running. At 240 it will run poorly. You will absolutely need to have in place the foam rubber insulation on the sides between the radiator and the radiator support. Also the Same goes for the top where the hood closes down on top of the radiator. When you don't have the insulation in place the air will come from around the sides and top of the radiator rather than through the radiator. Dr. Rebuild carries the good stuff. You should have a Robertshaw type of thermostat. I believe Mr. Gasket makes this product. It should be a 185 degree. Also be suspect of the parts you have already installed. Cheap hoses can have the spring inside collapse. This spring keeps the hoses round and not be able to collapse under suction. Cheap thermostats may not open at all or just barely. Did you install the thermostat correctly, the spring side goes down.

Let us know how you solve the Problem

Steve

 

You have to thank the poster(s) that suspected the sender. I've made it the 1st thing to check on my site.

 

Where can you get that foam material to build an air dam on top of the radiator?