overheating question

[Belgian1979]

I always thought it would be a good idea, particularly with ECU controlled fans, to have them come on at a quite low rpm when the car is stationary and the temp is over say 190 but but below the main turn on temperature. Have just a small breeze of air wafting through the radiator like the old days of non-clutch fans. Why let it creep up to the trip point unnecessarily?

Well, setting the fan trigger temp is a bit of juggling act. I can have 2 factors, but rpm is not really a factor here. You can have situation where in lower speed traffic (let say up to 35-40 mph) the car still gets hotter. The flow of air is strongly dependant on air speed and it has no issues over 40 mph. Prolonged driving at lower speeds makes the fans kick in at times.

[Belgian1979]

P.S. A Belgian using Fahrenheit... Weird....

He is being tolerant and polite to the provincials.

Actually all my readings in the ecu are in Fahrenheit. Makes it easier for me to keep track of things and most of the car is in US measurements (among others bolts and other sizes). Only thing I have in metric is the speed which is in kph for obvious reasons.

[Rick!]

What is the definition of a bypass?
You changed the cooling system to warm up faster and now it has less flow through the radiator at very low flow.
Put a valve in the bypass line and shut it off and see where the idle temp goes.
Most, not all, but most real bypass systems have a poppet valve on the thermostat to block off the bypass when the stat opens a bit. Pretty sure that Chevy never did that.

What happens when you turn the heater fan and command full heat at idle? Is it enough to stem the rising idle temp?

Other than that, you can take apart the pump and measure the pump vane to housing clearance and adjust it if it is more than .030". .010-015" is better and much tighter you won't see much for a measurable benefit. It should be just as tight on the back side also.
In general, the pump just creates head. The deltaP is measured as close to the center of the inlet and as close to the vanes as possible on the outlet side. When sized right, the same deltaP is created at the design RPM assuming a reasonable flow resistance is present in the system. Flow is pretty linear with RPM at a given flow resistance/equivalent orifice size so there is no magic except the RPM where flow knees over because it can't suck the volume needed to support flow there.

[Belgian1979]

Bypass is coolant from below the thermostat going directly to the top of the waterpump (suction side).

No there is no thermostat that shuts off the bypass for Chevy, which is why I was told to keep the line small in diameter (6AN)

[Geoff2]

If you completely block the bypass, you can blow out a Welsh plug at high rpms. Ask me how I know.....

[Robban 54]

If you connect a hose between the rear left socket on the intake and a new socket on the radiator next to the hose from the thermostat, you will get a bypass when the thermostat is closed and all water through the radiator when the thermostat is open.
Only slightly longer heating time in cold weather.
Have you looked at Edelbrock's two-piece water pump 8827
https://static.summitracing.com/global/ ... 827_xl.jpg
It has an aluminum impeller that is 3.5 inches in diameter with small tolerances.
I have it on my sbc 383 with only a 12 inch electric fan and have never had a heat problem. Ignition locked at 30 degrees plus 20 degrees vacuum.
Robban

[NewbVetteGuy]

I know the C3s are "bottom feeders"; I don't think it matters for IDLE and low speed cooling much at all, but are you referring to the PaceCar style front air dam, or the rubber "HD01" "Heavy Duty" cooling package's rubber air dam extension?

Knowing how meticulous you are with the details, I'm assuming you have installed the rad-to-support seals and you have an actual fan shroud and not just fans attached directly to the radiator without the shroud?

What's your coolant-to-water ratio? Pressure rating of your rad cap? -In the Belgian weather, I'd think you could go with a pretty water heavy mix to optimize cooling and a higher pressure cap to prevent boiling.


Adam

Hi adam,

It's the Pace car spoiler.
I might be mistaken but wasn't the electric fan an addition for when you have both HD cooling and AC? Mine doesn't have AC to deal with. I cannot mount that fan because the original radiator shroud has been removed since I put electric radiator fans in place. A disadvantage of the electric radiator fans is that it blows less air over the engine like with the factory fan. So it has a tendency to get hotter (especially due to the headers in the car)

All seals are in place to prevent escape around the radiator support and around the fan shroud. The shroud was custom made and envelops the entire core.
I should look the ratio up, but believe it is good to -20°C (-4°F). It's the old red type fluid and I believe it is 50/50 mix.
Cap is a regular style Corvette C3 cap. Coolant pressure is usually around 15 -18 psi.
Temps are in the -10°C in worst case scenario's in winter to 38°C during some moments in summer (10°F to 100°F)

I'm not sure on the electric fan and whether it automatically comes with Auto+AC or Auto+AC+L82 or ONLY on with the HD Cooling option.
Paragon Corvette sells a repro copy of the rubber HD01 air dam extension for $80 USD, but I'm sure shipping, taxes, and import duty would make it a terrible deal and I'm guessing you don't have any problems with cooling at speed...

Given your max cold temps you should be able to run a 75/25 water to coolant ratio with the addition of some anti-corrosive+water wetter; I'm sure your mix isn't the source of your problems, so I return you to your regularly scheduled troubleshooting thread, but if you can get it, the VP Racing "Cool Down" additive mixed at 1.5 oz / qt of DI water (44 ml / liter -ish) is essentially what the VP Racing "Stay-Frosty" Race Coolant is and makes it easy to move towards more water in the mix with an appropriate amount of anti corrosive.

Adam

[Walter R. Malik]

What is the definition of a bypass?
You changed the cooling system to warm up faster and now it has less flow through the radiator at very low flow.
Put a valve in the bypass line and shut it off and see where the idle temp goes.
Most, not all, but most real bypass systems have a poppet valve on the thermostat to block off the bypass when the stat opens a bit. Pretty sure that Chevy never did that.

Unless this is a Big Block Chevrolet engine, the "by-pass" in a small block Chevrolet engine is a passageway in the the block going from the passenger side deck directly into the water pump. There is no hose or any outside passageway.

[Bill Chase]

Did some tests. Ignition timing had no effect I could tell on the coolant temperature.

I do know from previous tests my engine is happier at around 195-200°F. I have tried a 180°F thermostat before but it seemed to have a negative effect on the way it runs and idles. I can imagine with a carb this may be different.

Thats the start up enrichment, and fueling/spark modifiers that are based on coolant temps in the ecu. All can, and should, be changed when going to cooler operating temps than the oem set it up for.

[Belgian1979]

What is the definition of a bypass?
You changed the cooling system to warm up faster and now it has less flow through the radiator at very low flow.
Put a valve in the bypass line and shut it off and see where the idle temp goes.
Most, not all, but most real bypass systems have a poppet valve on the thermostat to block off the bypass when the stat opens a bit. Pretty sure that Chevy never did that.

Unless this is a Big Block Chevrolet engine, the "by-pass" in a small block Chevrolet engine is a passageway in the the block going from the passenger side deck directly into the water pump. There is no hose or any outside passageway.

That is correct, but since the Stewart pump didn't have the hole, this was what they suggested as an alternative and it does work.

[Belgian1979]

Did some tests. Ignition timing had no effect I could tell on the coolant temperature.

I do know from previous tests my engine is happier at around 195-200°F. I have tried a 180°F thermostat before but it seemed to have a negative effect on the way it runs and idles. I can imagine with a carb this may be different.

Thats the start up enrichment, and fueling/spark modifiers that are based on coolant temps in the ecu. All can, and should, be changed when going to cooler operating temps than the oem set it up for.

Correct, but that is what I did, WUE always stops ca. 10°F before opening point of the thermostat.

[Circlotron]

If you completely block the bypass, you can blow out a Welsh plug at high rpms. Ask me how I know.....

A bit off topic but perhaps worth mentioning - the old wives tale about the engine overheating if you remove the thermostat *supposedly* because the water then makes such a quick trip through the radiator it doesn't have time to give up it's heat. If that was actually the case then the water going so fast wouldn't have a chance to pick up heat from the engine either...

What Geoff2 alludes to is a valid point - at high rpm the pump builds up a certain amount of pressure against the flow restriction of even a fully open thermostat and this additional pressure between the pump outlet and the thermostat would add to the existing vapour pressure and consequently help prevent any localised boiling. Take that restriction away and boiling is more likely, even at the same temperature.

[Rick!]

If you completely block the bypass, you can blow out a Welsh plug at high rpms. Ask me how I know.....

A bit off topic but perhaps worth mentioning - the old wives tale about the engine overheating if you remove the thermostat *supposedly* because the water then makes such a quick trip through the radiator it doesn't have time to give up it's heat. If that was actually the case then the water going so fast wouldn't have a chance to pick up heat from the engine either...

What Geoff2 alludes to is a valid point - at high rpm the pump builds up a certain amount of pressure against the flow restriction of even a fully open thermostat and this additional pressure between the pump outlet and the thermostat would add to the existing vapour pressure and consequently help prevent any localised boiling. Take that restriction away and boiling is more likely, even at the same temperature.

Whose old wife was working on cooling systems and baited everyone with this statement?

IF, there is an adequate heat exchanger in the system, the volume flow of the coolant will regulate the deltaT of the system. The deltaT of the system is managed by rules of thumb, experience, heuristics or copying what your neighbor is doing. The deltaT I aimed at was 15F max and the purpose was to minimize cylinder distortion during operation. Turning up the flow reduces the deltaT and slowing it down increases deltaT so one manages the flow at the operating point and hits the target deltaT. The bottom line is that steady state heat rejection rates should support the deltaT and flow rate you've installed in the system.

A stat is just a regulated flow restriction so once it's full open it just adds to the total flow restriction the of the engine system, fittings, hoses and heat exchanger. You don't get additive pressures in the system that run away uncontrolled. If you look at the head gasket you have a bunch of parallel flow orifices. Then the head has its own series of passages which may or may not sustain a flow velocity target to avoid local low pressures and the infamous localized boiling. Localized boiling can raise system pressure above what the pump will generate if that is what Circlotron is alluding to. At some point the relief in the pressure cap should engage and manage the excess pressure. Otherwise, a 2 Bar pump will create 2 Bar above the inlet pressure happily at the operating point and the system restriction regulates the pressure at the pump inlet. So, a high restriction system lowers pump inlet pressure and a low restriction will raise inlet pressure and the deltaP across the impeller remains at 2Bar. At idle and such low flow velocities, I would not suspect localized boiling causing the OP's temperature issue. He's already stated higher engine RPM "fixes" the condition so there seems to be underlying flow related issues. We don't have pix showing the coolant routing mods to/from the heads so that is another variable that has been added to the system along with the -6 bypass from below the stat to some point assumedly near the pump inlet.

So, the OP has a few things to ponder or maybe it's as simple as adding an IAC kicker at a programmed coolant temp and it's all better.
Or, maybe remove the paint from the radiator core.
Or employ an unpainted aluminum radiator.
Is the overflow reservoir/expansion tank still plumbed in the system?

BTW, there are cooling systems out there that do not perform well at excessive flow volumes but they aren't on a car. If the cooling medium has to change phase on the heat exchanger surface, that takes time, which is maybe where the old wive's tale came from?

[Belgian1979]

Well by the way it acts I would definately say it's a flow related issue combined with the thermostat not fully open.
Was wondering if an alu radiator would help with this, but these things are pretty expensive and if it doesn't help the money is out of the window for nothing.

Does anyone here have an idea how Stewart does in terms of vane-to-housing play in in their pumps?

Alltogether I might just have to live with it. Under driving conditions I have not seen any issues so far. Also, I don't know if the factory mechanical fan would have done any better as I used it in conjuction with a carb and the ECU was not there to give me actually temps. The factory gauge in the car is not really accurate in terms of what temp it is actually running.

[Tuner]

I don't recall the C3 Corvettes having to deal with the cooling system bleeding procedure the C4 and later cars require, but is it possible some air is trapped in the system that needs to be purged?