C4 Cooling Question

[MoeJr]

I was wonderign how my 84 Cooling system stacks up to others in this forum. I live in NH so it isn't warm now. The other day with temps of 40-45 the temps was about 200 while cruising but when I stopped and was waiting in the drive up line at the bank it got to 237 on the gauge. The fan kicks on at 233 according to the gauge at which point the temp climbs a few degrees before dropping fairly fast. As soon as I start moving it really drops fast. does this sound proper to you all? Thanks for all the info.

Moe

 

[Edmond]

Moe,

That is correct. Once you stop the car in traffic, there is no air being sucked in to cool the interior so the temps go up and the fan turns on. Once you get going, the fan will still be on (until 194 degrees, I think) and you have the air being sucked in from underneath. Therefore, the coolant temp drops real quick.

Just a note, the fans can be programmed to come on earlier to keep your temps down. Ask Jeff, the moderator, about that.

 

[geekinavette]

As Edmond said, that sounds about right. However the 84 cooling fan relay is not controlled by the ECM, it is controlled directly by a temp switch in the passenger's side cylinder head. You can install an aftermarket switch to turn the fan on at a lower temp.

Bill

 

[chgostout]

hey Moe -

I have a '90 convertible that I felt was running hotter than I was comfortable with, watching the temp gauge.
I have a great mechanic whom I refer to as "the professor" becasue he specializes in only c-4 corvettes, and knows soo much about 'em. He ordered and re-programmed a new computer module that controls when the fans come on (among other things). He re-programmed this chip to have both fans come on at 205 degrees and turn off at 200 degrees. I believe the thermostat is set at 190, so these fan settings don't interfere with it's operation.
The result is that while sitting still idle, the fans will both come on to keep the car cooler: And when the car is in motion, that will keep the car cool without the fans. Only on very hot days, with the air conditioning on, might the fans also need to be on periodically, even while the car is moving. In temps between 70 & 85, the fans keep the car at 200 degrees max. but even on the hottest days I've not seen the temp higher than 215-220.

He said GM set these higher temps for emissions control, becasue a hotter engine will run "cleaner", but all of that extra heat is also taking its toll on all the rubber & plastic in the car, not to mention the various metal and aluminum of the engine.

Ever since I had him do this for me, the car has run great... and much coooler! I just took the car on a 950 mi. round trip road trip, and the temp gauge didn't budge past 200 the whole trip!

I live in the Chicago area where we have hot summers and cold winters.

While your at re-progamming that module, also re-program it to advance the spark somewhat (I think about 10 degrees), and you'll about 10 more horsepower and about 10 more lbs. of torque out of the engine! He did this for me also, and said it was fine because we all burn premium gas in our cars, and the original factory setting for this was to accomodate running lower octane gas.

Good Luck ... and stay cool! ( I recently got personalized license plates for my car that reads ..." U Be Cool")!!

 

[MoeJr]

Geek I did buy a new factory temp switch but haven't installed it yet. Where can I get the lower temp ones? I replaced the one for the ecm temp already with a factory piece. That one is under the air pump.

 

[geekinavette]

Ecklers, Mid America...etc should have the lower temp fan switches. I believe they have an on-200/off-185 switch, and maybe other combos. I really don't know if local part stores would have the lower temp fan switch. Get yourself a lower temp 180 thermostat also.

Replacing the ECM temp sensor (CTS) is a good move, that is a very common source of problems.

Bill

 

[WhalePirot]

Step wise

The drops in temperature tells you that your cooling system is adequate as it is. The sudden drop is due to the airflow, either from your fan kicking in or from vehicle movement.

My '84s (Z-51) stock fan and radiator cooled my new 406 (500hp+) quite well; perhaps enough to not really need the BeCool radiator and FlowTech pump. The Robert Shaw (#330-180) thermostat made a big difference, by allowing increased coolant flow.

The '84 and '85 Vettes used, not the ECM, but a fan switch (sending unit) in the head on the pax side. I changed mine years ago, that switches the fan 'on' 210 (vs 230 stock). I am waiting to hear about a cooler one, that Chevy sells one for a Lumina or such, that is set for 195. I'm also told that an aftermarket adjustable switch will work well, which installs in the radiator.

I recommend taking this in steps. The car is designed to run hotter, for emissions and efficiency, but most of us wish to see cooler numbers. Start with the cooler swtch you have and ensure that leaves and road crap do not block airflow through the radiator.

Your stock cooling system is adequate for power increases, until you get probably twice the stock output, at least. Increasing airflow, at this point, seems the next, sensible approach, after the switch.

 

[MoeJr]

I will look for that switch. I would be happy for the fan to come on at 215.

 

[Edmond]

There's also a product called "Water Wetter" that I'm thinking of using in the spring. I guess it's supposed to drop the coolant temp by a few degrees without any mechanical modifications.

 

[geekinavette]

Re: Step wise

I'm also told that an aftermarket adjustable switch will work well, which installs in the radiator.

I made my own adjustable controller...it monitors the voltage at the temp gauge sending unit and turns the fan relay on/off accordingly. I had it set to turn on about 190 and off about 185 (with a 180 stat of course).

Increasing airflow, at this point, seems the next, sensible approach, after the switch.

That's my next step, to add a "pusher" fan and to improve the shrouding around the stock fan. I'm convinced that there just isn't enough airflow through the radiator.

Bill

 

[rrubel]

I recently added a pusher fan on manual switch, but darned if I can see much of a difference at all. Certainly none while sitting in traffic.

Water Wetter works... used to use it in my turbo RX. Used to get above midpoint in the summer without it; with it (and only it different) never even saw the middle of the gauge. And no rust or scaling when using plain water.
[RICHR]

 

[chgostout]

You guys seem to have the situtation well in hand. Sorry I was wrong about the control for the fans being in the ecm. It is in the'90 that I have, so I hope I've helped anyone with similiar problems who have a configuration like mine.

Be sure to periodically check and clean as best as possible, the front of the radiator and air conditioning condensor. Leaves, bugs, and even a candy wrapper I found up in the corner while looking up into the car - when I had it up on a lift recently, can prevent alot of airflow.

My corvette "professor" mechanic told me you have to take much of the whole front end of the engine compartment apart - just to replace the radiatior! And I want to hold that job off just as long as I possibly can!