160F Thermostat On 996 3.4 With California Smog

[JFP in PA]

So why isn't anyone discussing the radiator fans involvement here? While the thermostat regulates the minimum temperature coolant parameter, the cooling fans regulate the maximum temperature parameter, which is what most people are concerned with.

The coolant temp sensor signals low speed fan operation to begin at 206 deg F. and high speed is triggerd at 216 deg F.

With inadaquate airflow over the radiators like you would experience in slow traffic or worse yet a smog test, both thermoststs will be fully open and dependant on fan airflow to control engine temperature.

Have you ever had your electric fan fail? I have. Even on a cool San Francisco winter morning, you won't last 5 to 10 minutes in traffic with a failed electric fan before your coolant temp light goes on.

However, if you were not stuck in traffic and you were moving along with sufficient airflow over the radiators, the 160 deg F thermostat would lower engine coolant temperatures below the stock thermostat. And that bothers me. I would rather see my motor have a consistent coolant temperature than one that swings from 170 to 216. Is that wide band good for the motor?

In my opinion the only way the 160 deg thermostat can be helpful is if the fan sensor temps are changed to signal operation at lower temperatures. But new sensors are just part of the solution, you also need that 3rd radiator, otherwise the fans will be on all the time leading to premature fan wear or worse, potential fan failure.

So what is really needed is a kit that includes a reduced temp thermostat, new coolant temp sensors that operate at lower coolant temperatures and a 3rd radiator to reduce the load on the cooling fans.

To my knowledge, on the M96, the fans are triggered by the DME software when the coolant reaches pre set limits; so to change the temps you would need to alter the programming. As for the fan's run time, if you read the post from Australia, the fans tend to run less frequently and for shorter periods on cars with the 160F stat. We have also noted similar observations on both two and three radiator vehicles. The addition of the third radiator on cars only equipped with two would increase both the total coolant volume and total heat exchange surface area, both of which would further reduce fan run time even further (being aware that the third unit does not have a fan of its own, so its impact would become more important when air flow over the radiators returned).

[Stefan]

If the stock 185° thermostat is fully open at 200° (by your previous statement) and the fans turn go on low at 206° then both thermostats would be fully open before the fan came on. So with the exception of sudden temperature increases (not typical of stop-and-go traffic), if the fans are going on with the stock thermostat, they will also go on with the 160° thermostat.

[JFP in PA]

If the stock 185° thermostat is fully open at 200° (by your previous statement) and the fans turn go on low at 206° then both thermostats would be fully open before the fan came on. So with the exception of sudden temperature increases (not typical of stop-and-go traffic), if the fans are going on with the stock thermostat, they will also go on with the 160° thermostat.

Never said that they would not go on at the DME's preset temp, only that observations have been that it appears to take longer for the car to reach the first fan speed trip point temperature after becoming mired in traffic (which you would expect if the car was running at a lower base line temperature), that the fans do not appear to run as long a period of time before they shut off, and do not appear to run as frequently. Again, these are observations by multiple drivers, and have not been confirmed by any type of controlled experiment that I am aware of.

[pk2]

JPK,

Your methodology is quite thorough, extraordinary and has all the makings of a bid for a PhD. Add to that, all the time spent here defending it here leaves me with a more practical question; Exactly why the effort?

Regards, PK

P.S. Smog, why would someone with all the acumen of you and yours not be able to borrow some quality time on someone elses smog machine or cob together one yourselves with a dyno and some slightly obsolete (no longer certified…worthless) machine modules?

Edited April 5, 2010 by pk2

[Cefalu]

OK, so the time for the first cooling fan to actvate once you hit traffic is delayed with the 160 deg thermostat. I can see that, as you have the reduced thermal mass of 20 or so liters of coolant helping you out. However, once you are sitting there stuck in traffic, either thermostat ceases to play a role in controlling coolant temperature, as the car goes into a different mode. That mode being prevention from overheating as opposed to prevention from running too cold. The prevention from overheating aspect is controlled by DME fan programmimg. The prevention from running too cold is controlled by the thermostat. Actual operating temperatures fall in between these two controls.

It would make sense for the DME's preset programing to trigger fan activation. Then, all that is needed is to reprogram the fans to activate at a lower temperature, and the car could actually take advantage of the 160 deg thermostat when encountering a reduced airflow situation.

That said, I am fully in favor of finding a way to reduce coolant temps a bit. But it doesn't look to me that a 160 degree thermostat is going to help you once you are stuck in traffic, or have found yourself in a situation that has caused airflow over the radiator to be reduced. And, my guess is that most people who would be interested in lowering coolant temps would specifically expect them to be better controlled in a traffic situation, which for the most part won't be helped unless the DME is reprogrammed to activate the cooling fans at a lower temperature.

[JFP in PA]

JPK,

Your methodology is quite thorough, extraordinary and has all the makings of a bid for a PhD. Add to that, all the time spent here defending it here leaves me with a more practical question; Exactly why the effort?

Regards, PK

P.S. Smog, why would someone with all the acumen of you and yours not be able to borrow some quality time on someone elses smog machine or cob together one yourselves with a dyno and some slightly obsolete (no longer certified…worthless) machine modules?

Strange as it may sound, because I am in the automotive trade, and have been during my corporate career prior to going into business for my self, I developed an inherent "need to know" concerning just about anything and everything. I read about low temp stats for the M96, and decided to test how they compare for myself. Not that I mistrust vendors as much as some posters seem to, but I do firmly believe in "trust, but verify". And I run my shop this way. So when I read about opening rates and temperature differences, I looked up how stats are tested, built a similar test stand and ran some evaluations. When customers asked me to install them in their cars, it provided an opportunity to put a data logger in their car and see how both the units worked in the real world. Now, when a customer asks, I can give him an answer that I know I can support. If you think I'm nearly anal retentive over thermostats, don't get me started on what brand and weight oils and filters we recommend for the M96; because our choice is based upon literally hundreds of UoA's over many years, and more cut up oil filters than you could imagine...................

In the age of the internet, there are lot of questionable to unsupportable product claims bantered around almost daily. I like to sleep at night and not have to worry that the shop gave someone a "bum steer"; so we do more than a little leg work on our own...................

As for "smog", we do have a non-certified "sniffer" of our own, and we do have access to a nearby state licensed "smog shop" that does the state mandated emissions for our customers. I chose not to get my shop state certified simply because of the expense and paperwork involved; we can test, we just cannot certify compliance. We also do not do A/C systems recovery and recharge for the same reasons. We can test a system to see if it is up to snuff, but discharging, Freon recovery and recharge means submitting records to the state and federal authorities for every car, regular shop inspections, etc., etc. Too much trouble, and my approach allow me more time to focus on working with customers to keep them both happy and on the road.

Edited April 5, 2010 by JFP in PA

[Cefalu]

You will have a hard time getting any useful data while hooked to a smog machine. Here in CA they use a treadmill with a tailpipe probe and an OBD connection. They run the car at 25 mph on a treadmill. No airflow over the radiators, but the engine running at 25 mph and the vehicle at a dead standstill. Your cooling fans will be running and engine temps will be controlled by the DME fan controls, not a thermostat.

You would need to rig some sort of external cooling supplement to get coolant temperatures low enough while on the treadmill to see what effect the 160 degree thermostat has.

My only point here is everyone should understand that the 160 degree thermostat isn't going to help keeping coolant temps low once you stuck in traffic. At that point either thermostat is wide open and coolant temps are controlled by DME fan programming.

[JFP in PA]

You will have a hard time getting any useful data while hooked to a smog machine. Here in CA they use a treadmill with a tailpipe probe and an OBD connection. They run the car at 25 mph on a treadmill. No airflow over the radiators, but the engine running at 25 mph and the vehicle at a dead standstill. Your cooling fans will be running and engine temps will be controlled by the DME fan controls, not a thermostat.

You would need to rig some sort of external cooling supplement to get coolant temperatures low enough while on the treadmill to see what effect the 160 degree thermostat has.

My only point here is everyone should understand that the 160 degree thermostat isn't going to help keeping coolant temps low once you stuck in traffic. At that point either thermostat is wide open and coolant temps are controlled by DME fan programming.

I agree with your point completely. Areas in PA that require sniffers (usually larger metro areas) are not required to use rollers, the car is warmed up (often by taking to for a short drive), then connected to the sniffer. Shops like the one we use for state emissions have a four wheel chassis dyno with an airflow fan that they use to prevent unfortunate problems that occur when the 17 year old shop low-man takes a customer's year old Ferrari out to warm it up.

What the 160 stat will do for a car stuck in traffic is to take longer for it to get hot, and then allow it to cool back to the lower base line temp when it gets moving, which is were most cars spend the majority of their time...........at least those outside of the Bay area.................

Edited April 5, 2010 by JFP in PA

[Cefalu]

You will have a hard time getting any useful data while hooked to a smog machine. Here in CA they use a treadmill with a tailpipe probe and an OBD connection. They run the car at 25 mph on a treadmill. No airflow over the radiators, but the engine running at 25 mph and the vehicle at a dead standstill. Your cooling fans will be running and engine temps will be controlled by the DME fan controls, not a thermostat.

You would need to rig some sort of external cooling supplement to get coolant temperatures low enough while on the treadmill to see what effect the 160 degree thermostat has.

My only point here is everyone should understand that the 160 degree thermostat isn't going to help keeping coolant temps low once you stuck in traffic. At that point either thermostat is wide open and coolant temps are controlled by DME fan programming.

I agree with your point completely. Areas in PA that require sniffers (usually larger metro areas) are not required to use rollers, the car is warmed up (often by taking to for a short drive), then connected to the sniffer. Shops like the one we use for state emissions have a four wheel chassis dyno with an airflow fan that they use to prevent unfortunate problems that occur when the 17 year old shop low-man takes a customer's year old Ferrari out to warm it up.

What the 160 stat will do for a car stuck in traffic is to take longer for it to get hot, and then allow it to cool back to the lower base line temp when it gets moving, which is were most cars spend the majority of their time...........at least those outside of the Bay area.................

It could be worse, you could live in LA. It's just one giant traffic jam down there. The Bay Area is bad traffic wise, but it's a smaller area.

Your comments make sense to me. I am on the fence about the thermostat, but I think I understand better now what it will and won't do for me.