Temperature issues

[rgalajda]

Is it possible to remove the shroud, or open it up for more air flow at highway speeds ? Can the temperature gauge be tested for accuracy ?

[Bill Chase]

I have had an electric fan system cause highway overheating; excessively restrictive to airflow if the shroud forces all the air to go through the fan or fans.

Several oe gm setups shut off the fans at programmed speeds. The c4 corvettes did that above 35 mph. But, since his car was originally equipped with a mechanical fan maybe spacing the electric fan off the radiator with a shroud similar to what it had from the factory would help?

[BCjohnny]

Haven't read it all so apologies if this had already been said

It's a recent build on an older short block with no known cooling issues with the same heads and a single plane, single carb intake, mech fan on stock pump, similar bolt on parts etc. Sitting at idle, the fans cycle and it never gets above 195. Hopefully that helps narrow it down?

This is the crux of the problem and as has been pointed out the shrouding on your new set up is at least partly to blame

I don't wanna have to change the semi-serpentine stuff though bc it runs the power steering

It's not clear what you're saying here

If you're running RR and it's a normal CR impeller on the water pump that's at least part of your problem

If you're saying that you don't want to change back and put a clutched RR fan on the pump then that's something else

I'd personally go back to what worked and move forward from there


Otherwise .......

A lot of 'cooling' problems simple boil down (lol) to the simple fact that there's not enough reserve capacity in the system ....... in so much as once everything else is maxxed out as regards keeping the whole deal cool then merely fitting a 'bigger' rad will make the world of difference

[TheGreatPumpkin]

Haven't read it all so apologies if this had already been said

It's a recent build on an older short block with no known cooling issues with the same heads and a single plane, single carb intake, mech fan on stock pump, similar bolt on parts etc. Sitting at idle, the fans cycle and it never gets above 195. Hopefully that helps narrow it down?

This is the crux of the problem and as has been pointed out the shrouding on your new set up is at least partly to blame

I don't wanna have to change the semi-serpentine stuff though bc it runs the power steering

It's not clear what you're saying here

If you're running RR and it's a normal CR impeller on the water pump that's at least part of your problem

If you're saying that you don't want to change back and put a clutched RR fan on the pump then that's something else

I'd personally go back to what worked and move forward from there


Otherwise .......

A lot of 'cooling' problems simple boil down (lol) to the simple fact that there's not enough reserve capacity in the system ....... in so much as once everything else is maxxed out as regards keeping the whole deal cool then merely fitting a 'bigger' rad will make the world of difference

No worries, this has all been covered. It's an airflow and tuning/timing problem. Rad, fans, shroud, pump, etc are all good and appropriately sized/chosen

[TheGreatPumpkin]

Seems I could have been wrong about the airflow issue - I kept the same tune and ran it without the foglights or front license plate, and it's still behaving the same way. Not sure where to go next.

I know a lot of you have been saying to go back to the mech fan setup, but there is no room and I do not have the parts. I want to diagnose this setup without just throwing parts at it.

On the highway, when it gets up to 215 or so, I can let it coast, it drops a few degrees, and then when I put it back in gear and cruise at around 3000rpm it drops more significantly. That makes sense, since it's pulling cooler coolant into the engine after coasting. But does this mean that my problem is coolant-flow related?

EDIT: I have the front spoiler and will put it on asap

[TheGreatPumpkin]

I'm thinking the gauge reads about 10 degrees too high.

fan switch is 200 on/185 off, and the fans do cycle at idle, however the gauge gets up to 210.
at idle, upper hose is at 175-180, lower hose at 165-170. not a huge spread, but drops the gauge to around 195 or less.

[TheGreatPumpkin]

improvement seen. I upgraded my Spal fans to 1226cfm from 861cfm (each fan), changed to Zerex Original Green (from basic Prestone), and sealed all the gaps between the rad and the rad support to turn the rad support into a "scoop" to prevent air from bleeding off. Haven't put on the chin spoiler yet actually, I hate the way it looks in pics.

Fan switch is a Summit branded one, 200 on/185 off. Gauge is electronic Autometer Cobra style, bought new last year.

At idle, fans go on at 205 on the gauge, switch off at 195 on the gauge. Temp no longer runs away on the highway. Cruising at 65mph (2800rpm), temps get down to 195 on the gauge. Cruising at 80mph (3500rpm), temps get up to 205 on the gauge but stay there. Given the discrepancy between the fan switch and gauge, I'm not really sure what my actual temps are, but they are under control and in normal range or better, according to the gauge. If the gauge is wrong and the switch is right, even better. Can anyone recommend a very accurate fan switch or controller? Would love to be able to rely on either the gauge or the switch. Might test both in boiling water just to see.

[F-BIRD'88]

You could also try a front spoiler that is behind the bumper, directly beneith the radiator support.

You could also paint the front spoiler you have body colour instead of black, to visually hide it.

Might try making the holes in the fan shroud for the twin fans BIGGER size to allow more airflow at high vehicle speed. Or try ditching the fan shroud and mount your new large cfm fans directly on the radiator (no fan shroud). This will eliminate that shallow fan shroud as a radiator air flow restriction at high speed.

Good move on fixing up the ducting in front of the rad.

Yup high time to bench test the temp guage sender and fan switch temps.

[F-BIRD'88]

With fan power OFF how much effort is required to hand spin the fans fast, by hand. Fan motor dynoing effect. at higher vehicle speeds.
Any way you can reduce this fan dynoing effect at high speeds is a +++.
What happens when at high speeds you then power up the fans?

[TheGreatPumpkin]

I'm not about either of those things, there's not enough room to get my fingers into the fan to spin it like that. I don't know when the fans are on or off at speed because I don't have an indicator light. BUT I suspect they did go off since the gauge read 195 at 65mph cruise

[F-BIRD'88]

Spin your old fans by hand to get an idea of the fan motor dynoing effect at high speeds. This blocks high speed air flow.

[hoodeng]

Just out of interest, has the radiator been coolant flow tested recently? A radiator service shop will have the necessary equipment to give a percentage test.

[TheGreatPumpkin]

The rad is an aluminum Griffin unit, about a year old, I flushed it today when I changed coolants. No junk in it

[Geoff2]

It can still be blocked & no junk comes out.....

A simple test is to remove the lower hose & block the outlet. Fill the rad; then remove the cover from the lower outlet & watch how fast it drains. If it is pretty fast, that is good. If it takes a long time, then that is a good indication that the tubes are blocked. This is not a definitive test but it can help.
Also, cross flow radiators can block up the lower tubes with sediment, but that usually takes a lot of miles.

[jsgarage]

If you've actually tried all 3 pgs of suggestions and nothing has changed, a few more things to check:

1)- calibrate the temp gauge that has you worried. Or plug in a cheap replacement for a checkup. Generally, if the rad is not spitting water, its not overheating regardless of what the gauge says. To be sold in the U.S, any gauge must read to within +/- 2% of its scale at mid-range. "Precision" gauges must read closer than 2% to be legally sold. Bad electrical crimps or grounds are common- especially if you used teflon tape to seal a temp sender to the block. More than 1.0 wrap of the tape on pipe threads can insulate the sender and cause it to read poorly.

2)- electric fans are not linear with respect to air delivered vs voltage applied. A 1500 cfm 12v fan that only gets 10 volts will deliver about 50% of its rated air. Hot-wire your fan(s) directly to the battery and see if that noticably increases air movement. It's possible that a car's OEM wiring has developed poor connections somewhere in its loom. To solve my problem, I bought a cheap hand-held anemometer to actually find how much air was flowing. I found several areas in my car's grille where incoming air had found a way to avoid actually going thru the radiator.

3)- make very sure both sucker fan(s) actually suck air. Blowing air fwd from behind the rad with one sucker fan wired wrong will certainly cause overheating. A piece of paper held in the outflow (or in front of the rad) will tell you which way air is actually going without a gauge. Good luck.