Fast warm up ideas: Oil to coolant heat exchanger

[Daox]

Just trying to quantify things still...

If the purple vertical line here represents a 1% increase in fuel economy (per the test linked above), then the blue vertical line has to represent around a 3.5% increase in fuel economy. That is only at 60C / 140F. As the temperature drops, the difference in viscosity increases to quite a bit more. Our cSt at operating temps is about 13. An increase of 5 reduces fuel economy by 1%. Obviously it can't be completely linear, but the cSt at 0C / 32F is over 1400 for 10W30 oil. So, I think its safe to say that heating the oil up must have some pretty decent fuel economy benefits.

[ThermionicScott]

Originally Posted by Daox

Found a bit more info. Here is a oil temp vs viscosity chart. If the lines are THAT close together at normal operating temperature (~90°C), then at colder temps they are quite a bit more drastic.

Image from: Oil Viscosity Explained

Stuff like this is why I'm so ga-ga for 0W30 oils these days. Even if we don't often put the low-temperature specs (-35°C, yow) to the test, they'll flow much better after cold-weather starts than 5W_ and 10W_ oils. Just imagine what that chart would look like if extended to include some real cold temperatures.

[gumby79]

The data sheet is not copy ,pasteableChevronTexaco RPM® SAE 15W-40 Heavy Duty Motor Oil
Viscosity

6400 cP @Temperature -20.0 °C
6400 cP @Temperature -4.00 °F

cold crank

[Daox]

So, of course, this begs the question. What are DIY type ways we can use the coolant to heat up the engine oil?

[oil pan 4]

This heat exchanger is about the best idea I have.
I have also seen sandwich type heat exchangers that stack on to where the oil filter attaches. But I have only seen those on 4 cylinder diesel engines.

Actually if I can find a oil filter heat exchanger that is big enough I would just use that instead. I would only have to run coolant lines, as opposed to oil and coolant lines.

[Daox]

I've actually been looking into those sandwich types as well. They aren't super common, but can be found. I think this is probably the easiest ways to do this mod, although there are many other ways.

Honda has used them on quite a few engines including the CRX HF, Civic VX, and Insight (as well as a few others). I went and checked this morning and sure enough, I have one slapped to the block on my Insight.

For others not familiar with these, in the picture the silver thing you see that the oil filter is screwed to is not the block, its a device that circulates coolant through it. Thus, as the oil is flowing through it, it gets heated up.





So, I was like 'cool, I'll get one for my Prius'. Unfortunately, that won't really work. Honda uses a M20x1.5 thread on its oil filters. Toyota like many domestics I'd assume uses a 3/4"-16 thread. I searched ebay and was able to find one of these for a Tundra, but I haven't searched a ton. I assume that other manufacturers have similar parts, its just a matter of finding them. FYI if you're looking, they're typically referred to as an 'oil cooler' as they will cool the oil with the coolant when the oil gets warmer than the coolant. Thus, I believe its also used on the Integra and Prelude engines as well.

Here are a few more pictures of the Honda ones to give an idea of what they are and how they work. I'm really surprised we haven't talked about these before on EM. I searched and was only able to find one really old thread where it was mentioned, but not really discussed in any depth.

[Stubby79]

Until the engine is running, or the oil is otherwise being made to flow, I don't see it heating a lot of the oil. If the engine is running, the oil will get warmed up rather quickly from the already pre-heated block as soon as it gets flowing.

You could flow hot coolant through your oil pan, similar to your idea of installing heater elements in the pan. But if/when they leak, your engine is in trouble.

Can you make the oil flow through a non-running engine somehow? Then the engine block is your heat exchanger.

Spinning the whole engine would waste too much power. Doubt you can spin the oil pump with it still attached to whatever drives it in the engine. So...an external pump with it's own pick-up tube, pumping oil up in to one of the rocker covers? Well...now we're just getting complicated...

[Daox]

Originally Posted by Stubby79

Until the engine is running, or the oil is otherwise being made to flow, I don't see it heating a lot of the oil.

Completely correct.

If the engine is running, the oil will get warmed up rather quickly from the already pre-heated block as soon as it gets flowing.

This is exactly what I thought, but apparently its not really the case. Oil Pan posted a bit ago that his oil pressure doesn't drop until significantly after the coolant is at operating temperature. Temperature testing would be very interesting to see how oil temp lags behind coolant temp.

You could flow hot coolant through your oil pan, similar to your idea of installing heater elements in the pan. But if/when they leak, your engine is in trouble.

Can you make the oil flow through a non-running engine somehow? Then the engine block is your heat exchanger.

Spinning the whole engine would waste too much power. Doubt you can spin the oil pump with it still attached to whatever drives it in the engine. So...an external pump with it's own pick-up tube, pumping oil up in to one of the rocker covers? Well...now we're just getting complicated...

Quite true, if you want to get beyond this point, it starts getting more complex. I do like the idea of flowing coolant through a heat exchanger in the oil pan. This gives us the opportunity to preheat the oil with the block heater, but we'd likely need an electric water pump. IMO this would be a lot easier than trying to flow oil without the engine running, but still not easy or cheap.

Of course, we can also use a pad heater on the oil pan to heat it up as well. But, that only works when you can plug in, and the heat exchanger works everywhere all the time.

[ThermionicScott]

That is a pretty cool find, Daox. I wonder if the main purpose is actually to cool the oil once up to temp, though. Engine wear/longevity is improved if you have a way to keep your 5W30, 5W20, and now 0W20 oils from getting too thin with a hot engine. In the earlier cars you mention, the VIIs of the time may have been one of the concerns driving this inclusion, as high heats are murder on them.

But since oil temps lag coolant temps during warmup, it is a nice way to get a little more heat into the oil sooner. Pretty slick.

[oil pan 4]

You could pressurize the oil with a 12v gear pump. But I don't see any advantage to the expense and complexity involved.

The oil does heat up through the block but it also loses heat through the sheet metal on the oil pan.