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HNNLIC
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Discussion Starter · #1 ·
After watching numerous performance shows about both Domestic muscle and Imports, a few things have continued to be talked about on every show.

There are a few peices that can be easily added to the engine to help keep engine temps down, so the ECU doesn't retard the timing during hard driving or racing.

The pieces that have been added on include:

- A radiator cap that relieves pressure up to a certain point
- A race thermostat, that allows the engine temps to be cooler
- A sensor that allows the cooling fan to turn on earlier

I know the description are somewhat vague, but what have other people heard regarding these add-ons?
 

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All of the above I'd say. Or if you're building an engine, getting the pistons, combustion chambers, exhaust ports, and valves ceramic coated will make it run MUCH cooler.

Adrian~
 

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Blaque_Out said:
- A radiator cap that relieves pressure up to a certain point
If you mean a cap with a higher pressure rating than the stock, it won't help unless you are getting so hot that you're blowing the stock cap on a regular basis. And I doubt anyone's getting *that* hot in a modern car. Many domestic muscle cars rely on ainchient technology though, so I'm not suprised it's a common upgrade.

The only time I'd expect it to be necessary in a modern car would be if you're running a non-stock coolant mix that operates at a much higher pressure than regular coolant. This is common in track prepped cars, but I don't see a reason to get this extreme in a street car.

- A race thermostat, that allows the engine temps to be cooler
- A sensor that allows the cooling fan to turn on earlier
The danger here is that many modern cars have a seperate temp sensor that tells the ECU when the car has reached a certain temperature range, and changes the fueling program accordingly when a certain "warm-up" temp has been reached. If you use a temp switch and/or thermostat that's too low, you might never reach that point - and thus you'll be running too rich most of the time. So, you're either stuck with only making small adjustments that might not be effective, or you've got to gamble that this won't apply in your situation - or figure out a way to trick the ECU's temp sensor.

Speaking from VW experience, there are a whole range of temp switches and thermostats available to do these things, but I don't know if they are available for Saabs. The VW bits are just standard-issue Bosch parts though, maybe Saab uses generic parts, too.

I know the description are somewhat vague, but what have other people heard regarding these add-ons?
My theory is that if it works, don't change it. Cooling systems on the vast majority of modern cars are designed well over capacity. IMHO, you'd probably get better results by doing things to cool the intake air - most of our mods are done to increase boost pressures, which increases intake temps well beyond design limits. Sure, we're asking the cooling system to do more work, but IMHO it's as much of a difference as the increase in intake temps.
 

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Saab made two thermostats, 82C and 89C. The 900 and 9-3 use the 89C and the 9000 uses the 82C because its cooling system isn’t as efficient. The thermostats are interchangeable so you could drop in the cooler one. As far as I know the 82C stat works fine but as Driver Found mentioned the system is complex. Running a cooler engine might decrease it’s efficiency and loose hp. I don’t know what the temperature threshold is. Some test would be great.
 

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ERP said:
Running a cooler engine might decrease it's efficiency and loose hp. I don't know what the temperature threshold is. Some test would be great.
If someone could find out where the ECU's temp sensor is it's pretty easy to find their opening point in a pot of hot water with a thermometer. Then you know your safety point. Assuming it was an open/closed switch and not variable resistance.

Like you said though, it's easy to decrease the temperature of the whole system to a point where combustion isn't happening at the right temp. But I wonder how easy that would be to accomplish during a high-boost run with hot intake air. Again, speaking from experience with boosted VW's, you hit the cold-start enrichment before you decrease temps *that* much.
 

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HNNLIC
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Discussion Starter · #6 ·
My main reason for bringing this up wasn't to just change out stock parts, but because these devices (maybe not so much the radiator cap) help prevent the engine from retarding the timing, by keeping temps low.

As we all know our ECU constantly adjust timing according to our driving, so if we suddenly wanted more power than we normally use, the ECU won't hold back.

I think if we did find out the exact temp that the ECU started to do this, then we could infact keep temps low enough for ECU not to cut back, but for the temps to stay around normal for the fuel mixture to remain balanced.
 

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Blaque_Out said:
I think if we did find out the exact temp that the ECU started to do this, then we could infact keep temps low enough for ECU not to cut back, but for the temps to stay around normal for the fuel mixture to remain balanced.
Ced, I think you'd be much better off trying to accomplish that by lowering the air intake temps, not the coolant temp - unless Trionic monitors water temp and adjusts tuning in response to that? That would be a pretty outrageous thing for an ECU to do, beyond the simple point of cold start enrichment.
 

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The coolant temp is monitored by the ECU but it is not used in the air/fuel ratio calculations. With my OBD2 software I can monitor the coolant temp. With the 89C, 192F thermostat, coolant temps are usually around 210 F. The 82C thermostat is only 12F cooler. I might give it a try. The reason being to decrease engine block temps 10-15 F and decrease heat soak to the intake air. I remember seeing someone test both thermostats in some boiling water and had a picture of it. I think it was on Saabnet.
 

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Lower temperatures also mean worse fuel mileage and worse emmissions.

Having cooler coolant means cooler pistons, cyllinder head, valves etc ... if those are cooler the boundary layer of air that normally insulates them from combustion is thicker. The boundary layer contains the standard mixture of air/fuel like the rest of the cyllinder and doesn't burn. The thicker it is, the more air/fuel doesn't burn, the more emmissions you emiit, the more fuel it takes to move the car.

In the summer I would reccomend the cooler t-stat for power. It will reduce the tendancy to knock, and you should be able to get more boost as a result. In the winter I would NOT reccomend it, as it is not necessary.

For what it's worth, the Toro fuel additive I use has give the car all the power I would normally see in the winter even in the hot summer months. It's a bit more expensive, but if anything the mileage has improved slightly. I doubt a different thermostat would be as effective as ~95 AON.

Adrian~
 

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What about switching to a cooler plug for summer months? Would this provide a similar benefit...maybe running a 7 half the year and an 8 the other half?
 
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