Hi folks, just got a 74 with a 350 in it. Drove it 300 miles home no issues and sat on 195 degs all way home and getting up to 205 ish in town or traffic. Has a new fan switch installed last week which makes the fan come on at 200 and is suppose to shut of at 190 but it doesnt get down to 190 so fan stays on once up to temp. The coolant is only at 15% so would a radiator flush and replace coolant help or should i change t/stat.
Any advice greatly recieved. Cheers doug

 

Since you just got it you know nothing about the condition of the cooling system or tune of the engine. If you came home 300 miles at 195 best bet is you have a 195 T-stat. I would flush cooling system, replace the T-stat with a 180 and if possible reset the fans (assumed you have electric from comment) to on at 190 off at 170. Also, go over the distributor advance to make sure it is ok and not too wild and ck out the timing. Look at your shroud if it still has one. ck out seals on both sides of the radiator to see if they are still there. If it has AC a good wash of the condenser coil is in order along with the radiator. Look for the "air deflector" under the front end. Read up on the 100's of posts on cooling issues on the forum, do a search for cooling.

Look at the design of the vettes as far as radiator placement, angle and engine compartment. Unattended design to run hot until moving. All has to be right so it does not.

Again send Lars G a note at V8FastCars@msn.com and ask for his papers on timing and engine tune. It is a learning process that should be a good hobby.

 

I suspect that the cooling system has a 195*F thermostat in it, which is exactly what a '74 engine should have. Running close to 200*F all the time is just about ideal for an engine with that stat.

So, the engine is not "too warm". If YOU are too hot in the interior, that's another issue.

 

I agree with everything except for this. Why would you want the fan to shut off at a temp below the thermostat? It'll run constantly (like it does now). There's absolutely nothing wrong with "on" at 200 and off at "190" with a 180 thermostat.

 

You have the wrong switch. '74s didn't come with electric fans so who knows what some previous owner installed.

 

Thanks mate, thats the problem with getting a car that has had 40 years worth of tinkering and changes eh. Cheers

 

Hi mate, I'm only learning all about my Corvette and enjoying the process thanks to your feedback. I agree with you and since the fan switch is new and im happy with the on at 200 and off at 190 setting will just change the stat to 180. Was confused way you'd have the fan set lower than the stat as i think this is whats happening at present and the fan wont get the car cool enough because its battling the stat which is around the same setting.
Anyway, will give the system a flush and replace stat with a 180. Thanks for everyones help. Cheers Doug

 

To give you some perspective on what's "hot," the 1985 Vette, with the same engine in it, has electric fans as stock equipment, along with a 195 thermostat. The fans are programmed to come "on" at 230, and they shut off at 217. Any temp between 195 and 217 is considered too cold to justify running the fans. Hot is anything over 230, and the engine will shut itself down (ECM-induced shutdown without any damage) at 260 (at which point it will boil over).

To save yourself a bunch of needless power to run the fans (electric fans bog the alternator down like you wouldn't believe), I'd set the "on" temp at 220 and the "off" at 200. That will prevent the fans from running under most cruise conditions, when the temp will tend to stay at about 200-205 without fans, which is perfectly fine and normal. Also, keep in mind that the thermostat controls minimum temperature and not maximum..

Lars

 

Your cooling system is fine. Making the switch adjustments that Lars recommended will optimize the system you presently have.

 

I had very similar issues. I got my '76 about three years ago and it had a OEM brass radiator that blew a hole last Fall. I was going to get an expensive radiator but settled on a Champion 2 row with two electric fans. Here are the things I learned from Lars, a few others and my own experience...

The foam seal kits that you buy won't fit snug. Your best bet is to get window air conditioner open cell 2.25" thick foam (http://www.lowes.com/pd_69405-81-025...=#BVRRWidgetID). You mount this using 4 inch 10lbs double sided tape strips with space the strip between all around the radiator's edges as well as the top edge of the radiator core mount. This will absolutely seal your 3rd party radiator so that ALL incoming air will be forced through the radiator. And the seal will far exceed the $30+ kits for a measly $2 for every 3 feet of foam needed. The foam is open cell so it will collapse to fit and has such a great deal of surface area that it will stay between the items installed within.

I have dual fans but what really matters is that they are mounted on a fan shroud. These electric fan dealers will sell those plastic mounts that go through a radiator to mount the fan. Do not use those. Spend the extra and get a fan shroud for the size fans you have and properly mount them. This will ensure that the air pull goes through ALL of the radiator and not just the area where the fans are mounted.

For a thermostat, I use 180F because as Lars also told me this the minimum operating temperature. The thermostat has nothing to do with the maximum, that's where your radiator, fans and water pump come in...

For controlling the fans, I have a 40Amp relay which has the fans triggered to go on at 205F and off at 195F. My fans only come on when I am sitting still for a few minutes. Once I get moving, the fans completely shut down.

Also, I use a radiator cap which has a flange on it for letting out air. This is very useful to bleed the system out through your reservoir tank. Oh, that's another important item. Make sure your reservoir tank has the correct rubber pipes installed! Mine was missing the pipes inside that connect to the cap... I fixed that and now the radiator is always full as long as I keep that reservoir properly filled.

 

Thanks Bacalou: I just put the same set up in my 75, however I installed them with the fan through the rad mounts. part of the rad was cool the top part was very hot. Granted I still have the front cap off the car. I can't run the engine for more then about 18 min without it getting real hot (220+) I took the guts out of the stat to help improve circulation. (i live in South Fla. getting up to temp isn't normally a problem) . I am now going to seek out a shroud for those fans and give it another try.

 

Yes, you MUST have a shroud for those fans. Those silly plastic mounts only will cool the surface area directly below the fans. I had the same issue with my engine overheating when I was using the plastic mounts. Once I went with a proper shroud, my engine has a variance of about 15 degrees with the fans going on and off while the car sits in my driveway.

I have found the 2nd most important thing is to make sure that the radiator, shroud and radiator frame is all properly sealed up. These cars, when moving, rely on an air scoop located under the nose to force air in and through the radiator onto the engine bay. Without that air scoop, your car overheats when moving, Without proper seals, your car overheats when going over 45mph.

 

Buy the way Bacalou where did you get your shroud?

 

I have a Champion radiator so I ordered the shroud directly from them.

http://www.championradiators.com/aluminum-fan-shrouds

Just choose your radiator model # and they'll show the matching shroud.; if yours is a Champion. Otherwise, check with the manufacture of your radiator for recommended shrouds.

 

Thanks I have the champion 2 row alumiumn also, will contact them when I get home

 

I am currently installing a 3-row Champion with an aluminum shroud that houses two electric fans. Not installed yet, but I am happy with what I have seen so far. Bacalou, I will take your advice about the window air conditioner foam, and will return the $30 stock pieces I purchased months ago. Bought a dual wiring harness from Jegs that should be here on Saturday. Looking forward to getting it in and start driving. It has been a long winter.

John

 

Here's a photo of my installed radiator, shroud & fans. This was a test setup to see how well the Window AC foam did versus the foam kit. With the test being successful, I replaced all the kit foam with this type. I'll post another photo soon with the full AC foam installation.

 

Here is the photo with the fully sealed radiator using Window AC 2.25" insulation and 10lbs double sided weather resistant tape. My fans only come on with the car is sitting still. Once I get above 20mph, the fans stay off until I'm sitting still again. Yes, it does look a bit over the top or even worse than the OEM foam kits but the seal made by this insulation is perfect. I have it on the bottom, sides, top and between the hood & radiator core support. It costs $2 per 3 feet.

 

OP do you have electric fans with a mechanical fan ? if so do you have a clutch on the fan .what pulley sizes do have for the crank and water pump ?mite need a new water pump .what the coolant fluid level when you last checked ? also consider installing a thermostat housing with a radiator cap on top .this allows you to bleed the air out of the coolant system easier .

 

how does the fan shroud mount to the radiator?