Using engine oil to heat car cabin

[azmaway]

I am a relative newcomer to the 911 community and I thought I would put this out there for consideration and discussion. As a Mechanical Engineer having worked in the steel industry, specializing in the design and commissioning of large recirculating lubrication systems, I was intrigued with the engine lube system on my 1979 SC. I will save any critique regarding the actual lubrication system design for another thread. Right now I would like to ask if anyone has ever come across a modification for heating the car using the engine oil via a heat exchanger; just like on a water cooled engine?

It seems to me that heating air via the exhaust manifold and then diverting it into the car is a very cumbersome and inefficient way of doing things; the air pumps/motors; exhaust heat exchangers; hoses and ducting occupy huge amounts of space and the control system is overly complex for what it does.

Using hot oil is not a great deal different than using water on a water cooled car for heating. Having the luxury of a large oil reservoir on the 911’s enables you to take oil from the tank via a small, electrically driven pump (possibly just one GPM) and send it to a heat exchanger located somewhere on the trunk side of the bulkhead. The oil would then be pumped back to the oil tank. A fan can then send warm air into the usual heater hoses, into the cabin. Taking oil directly from the tank safely isolates the heating system from the engine lubrication side of the system.

I know it takes the car considerably away from original and I personally wouldn’t do it to my79 SC. However, I was just curious if anyone has ever done this before, and if so, how was it done. It is relatively simple to work out oil flow requirements; heat exchanger sizes etc. and arrive at a kW value of heat power available for the cabin.

Any comments would be more than welcome.

[ClickClickBoom]

Pretty sure the good Dr. had batted this one around. Removing heat from the oil, might not be the best, not all heat is waste, if you cool the oil too much you have to heat it back up and that could cause the Law of Unintended Consequences to be invoked. Generally the only time the oil has excess heat is when you would like it least, ie hot days. While almost all heat coming off of the exhaust is waste/unneeded/undesired. Most everything downstream of the exhaust valve has little value, unless you are turbocharging, and that's a fish of a different color.

[Hil911]

I wonder if there are perceived safety issues? Didn't they ban direct-feed oil pressure gauges for that reason?

And ClickClickBoom is right: just like heating with reverse-cycle air-con: it would be great right when you didn't want it!

[82 SC]

When all the stock heater parts are there and working correct the heat from the stock heater boxes work pretty well. Way better than my heat for my old vw buss but heating an entire bus is harder with a little 4 cylinder motor vs a tiny interior with a 6 cylinder motor. Now if you live in a very cold climate they do make gas powered auxlieray heaters like the ones from eberspaecher. Eberspächer - Exhaust Technology, Vehicle Heaters, Automotive Electronics
VW has been using eberspaecher for a long time and I would think Porsche does too.

[Jp-oh]

Where I live it's cool enough a lot of the year that I'm often wishing to add heat to the oil :s

[82 SC]

Jp-oh do you use a engine block heater to keep your cars warm to start them in the winter?

[GH85Carrera]

You did not give your location. That oil heat might be OK on a cool humid day in the 50s.

I drove my 911 on ZERO degree temperatures last winter. I drove for two hours and the oil temperature never got to even warm. No way would you get the engine hot enough to open the thermostat to send oil up front. I don't think I got my oil temp up to 160 degrees and that was after a lot of driving.

[sc_rufctr]

Good idea but it's less than ideal. A better solution IMO would be to modify the air conditioning so it runs in reverse cycle just like in a house.

This is more doable now than ever before because you can buy electrically driven compressors instead of the traditional kind that are driven off the engine.
I'd imagine it wouldn't be that hard to find room for it in the "frunk".

These still are from Chris Harris, "Chris on Camera - YouTube" in the UK. This is his own car with custom modified climate control.





As mentioned above the OEM system can be very efficient when it's in good order.
FYI... A friend used to heat cans of food next to the floor vents in his early 911. This was when I was in my 20s and it worked very well.
That car was either blast furnace HOT when it was fully warmed up.

[boyt911sc]

Originally Posted by GH85Carrera

You did not give your location. That oil heat might be OK on a cool humid day in the 50s.

I drove my 911 on ZERO degree temperatures last winter. I drove for two hours and the oil temperature never got to even warm. No way would you get the engine hot enough to open the thermostat to send oil up front. I don't think I got my oil temp up to 160 degrees and that was after a lot of driving.

Azmaway,

Get to know your car. Your idea is an interesting concept but will not work in air cooled 911. Driving your SC in the winter when temperature is in the 30's will not get your engine oil temperature hot enough for sufficient heat transfer. Demonstrate the feasibility of your idea by doing some initial testing and experiment. Good luck.

Tony

[cgarr]

What about a gas heater? My 912 still has one in it.

[sc_rufctr]

Originally Posted by cgarr

What about a gas heater? My 912 still has one in it.

Gas heaters are brilliant. The problem is original 911 gas heaters in good condition are expensive.

[82 SC]

which model does heater your 912 have? if it is like the vw crowd the price is not too bad for a gas heater but finding the duc work might be interesting for a 911. I use to have a VW thing and it only had a BN4 eberspaecher heater for heat, it was kind of quirky but did a great job since the VW think has no insulation at all to keep you warm.

[chris_seven]

Despite there being plenty of heat in the oil (30% of engine power?) I would think it very unlikely that you would find an oil cooler with sufficient heat dissipation to do the job.

There are several new Petrol Burning heaters available to do the job and modern units are Intrinsically Safe and Microprocessor controlled.

We are just about to fit one to a 1979 911SC and it cost around $1000.

[McLaren-TAG]

I think to answer the question in the OP you have to think about the original design of the car. When you backdate heat, you lose a lot of the cumbersome stuff in the engine bay and a lot of people go as far as removing the footwell blowers as well.

Adding the complexity of additional oil piping in the end, isn't that much more efficient. You still need the engine fan to cool the engine, what's being added it simply the shielding around the headers which doesn't weigh that much and routing the air though existing chassis structure support.

If you ask me, it doesn't get much more efficient and light weight than what was originally there when the car was designed.

[wwest]

Could get....MESSY!

I would encase the front fender oil cooler with a water/coolant jacket and then pump the coolant to a cabin heat exchanger.

But you would likely need a thermostatically controlled louver system in the rear lid grille airflow path such as used in many diesel freight hauler trucks to keep the engine temp elevated to the proper operating temperature.

With stock heating system my '88 can just barely keep the windshield defogged in the wintertime over our mountain passes let alone heat the cabin to within a reasonable comfort level.

[Trackrash]

I considered doing this to my hot rodded VW Baja bug. I have headers, so no heat as it is.

I think it would work for me. My VW only has one oil cooler, which is mounted outside above the motor. My factory cooler that used to be in the cooling fan has been eliminated.

I would add a second oil cooler in the trunk above my knees, with vent holes and a fan to direct the warm air into the cabin.

I would have a valve in the oil line to direct the oil flow to the cooler in the trunk and NOT the other cooler during cold weather.

In a 911 if you could block off the engine oil cooler, maybe an in-cabin cooler could work for heat?

[Jp-oh]

Originally Posted by 82 SC

Jp-oh do you use a engine block heater to keep your cars warm to start them in the winter?

I had an oilpan heater on my V8 S4 that worked well. It had about 10 l of oil in it too so it took foreve to heat.

I tried a zero start magnet heater for tha 911s oil tank but the shape of the tank made it too awkward. I may still look into a pad heater for the 911; they are available in a variety of sizes and shapes and basically glue on.

Every new car in alberta more or less comes preordered by the dealer with a block heater. My Tundra sits outside so I plug it in periodically when it's stupid cold otherwise I'll still be frozen by the time I get to the office.