Pre-heating: Oil vs Water

[oldtamiyaphile]

(Questions in bold for people who don't want to read the whole thing )

The next project I want to do on my van is some sort of engine pre-heating.

I notice most of the threads on here are about people fitting water/ block heaters.

It's well known that water has a much lower heat capacity than oil and that therefore oil temps take longer to reach optimal than oil temps.

I have a 1.6 turbo diesel, there's not much waste heat - plus the oil pan holds a massive (for a 1.6) 7.4l (7.8 quarts). I know in my old VW that was leaking fuel into the oil it used to take a good 10km (6miles) to get the water up to temp (when I drained the oil and found 11 litres in there I found my problem). Just shows the heat capacity of oil, once drained and filled to half way on the dip stick warm up was a normal ~2km. Another time I got an old Suzuki/Metro and the oil was thick and disgusting - hadn't been changed in years. Took for ever to warm up. Change the oil and it was one of the fastest to warm up cars I'd ever owned.

So my plan is to buy a stick on Wolverine oil pan heater, as they come in 240v models (normal mains power here).

The plan is to run off my van mounted solar panels, off an inverter.

My thought is to just connect the inverter to the solar controller out put, so when ever the sun shines the oil is being warmed.

Other than possibly burning out the heater pad sooner, would there be any reason not to have the oil warmed, even when not being driven?

I like the idea of the oil being warm and ready to go whenever I am. I can still have an automated timer or kill switch for when I know it's really not going to be needed, but if I can leave it on all day it would be really convenient.

Since I'm stepping up the voltage from 12v to mains voltage I can choose either a 110v or 240v inverter - I know 240v is theoretically more efficient, but I think the inverter becomes less efficient, as well as bigger and more expensive?

I also see these 12v units that would do away with inverters:

https://www.aliexpress.com/item/100X...80e2b74c8b30-0

Fairly cheap too -and I like the in built thermostat. Even with 360W of solar panels I think any pre-heater will have to be switched off once moving - or at least once warm.

Based on other people's tests, I'm aiming for 250W - in reality that's more than my panels would normally produce but I don't think that matters. I'll probably warm the trans while I'm at it. My primary reason is because I really want this vehicle to last me 20+ years, so no cold starts

Finally, given that oil pan heaters are so much easier to install, and can't possibly cause a leak of vital fluids, why are most of you heating water rather than oil?

[Daox]

Originally Posted by oldtamiyaphile

It's well known that water has a much lower heat capacity than oil and that therefore oil temps take longer to reach optimal than oil temps.

I think you have this backwards. Water holds 1 cal/gram°C. Oil hold from .4 to .5 cal/gram°C depending on the oil. That means if we have both fluids of equal volume that are heated at the same rate, the oil would heat up roughly twice as fast.

https://www.engineeringtoolbox.com/s...ity-d_391.html


That being said, heating your oil is a great idea. It will reduce oil pump losses which have to be pretty high with real thick oil, and they reduce engine wear.

Personally, I would try to find a 12V pad heater if solar is the only way you're going to power it. It just makes the system way more simple, and less components to break in the future. I know we like to think all electronics should last forever, but they don't sadly.

I think more of us don't do this, because we can get much more powerful block heaters. Standard block heaters are 300-400W, and more is better IMO. If you can warm the block, it'll warm the oil. If you warm the oil, but the block is cold, it'll cool down the oil. Ideally, you really want to do both.

I also see no reason not to run the heater all the time. As long as you don't overheat the oil its not going to hurt anything.

[oil pan 4]

The stick on ones kind of suck.
You can not connect a stand alone inverter directly to solar panels. The panel ocv is too high for the inverter, then under load it will likely undervolt fault.

I have several posts on heating oil. None involve stick on heaters.

[redpoint5]

Coolant temp affects engine warmup, and a faster warmup means less time running a high idle speed. Also, cabin heat comes from coolant temp, so this improves cabin comfort.

I suppose warming the oil from the PV panel is better than not using it at all, but my preference would be to feed the energy back into the grid.

[oldtamiyaphile]

Originally Posted by Daox

I think you have this backwards. Water holds 1 cal/gram°C. Oil hold from .4 to .5 cal/gram°C depending on the oil. That means if we have both fluids of equal volume that are heated at the same rate, the oil would heat up roughly twice as fast.

Indeed I was possibly confusing with boiling point.

Personally, I would try to find a 12V pad heater if solar is the only way you're going to power it. It just makes the system way more simple, and less components to break in the future. I know we like to think all electronics should last forever, but they don't sadly.

The conundrum is that the inverter could be used to run the odd mains powered tool or charger. I feel that the probably higher quality mains heater is likely the more robust solution, but also the more expensive.

I think I'll try the cheap 12v heater first - the 80*C thermostat is a major draw card. I can't imagine that temperature ever harming the oil.

Originally Posted by oil pan 4

The stick on ones kind of suck.
You can not connect a stand alone inverter directly to solar panels. The panel ocv is too high for the inverter, then under load it will likely undervolt fault.

I have several posts on heating oil. None involve stick on heaters.

I have solar controllers of course. The inverter would be running off that, or failing that off the battery via a relay connected to the controller load.

Bare in mind factory warranty - stick on is about my only option for the moment. I accept it's not the most effective option, an immersion heater will have to wait.

[oldtamiyaphile]

Originally Posted by redpoint5

I suppose warming the oil from the PV panel is better than not using it at all, but my preference would be to feed the energy back into the grid.

I've only got 360W of panels, so there's really not much energy to plug out -most of it's already used inside the vehicle.

I'd say a plug out conversion makes little sense- assuming you leave home in the morning and come home in the evening. I'd get about 2kWh per week- about $20 a year saved - vs the cost of a grid tie inverter and the hassle of plugging in, and you know one day you'll drive off with the plug still attached.

[cRiPpLe_rOoStEr]

Maybe an oil heater is not so bad to make it flow easier right after the start, but a coolant heater still seems to be the safest option for engine pre-heating and shouldn't be disconsidered.

[gumby79]

Turbo diesel may alredy have a coolent /oil heat exchanger. My stock block heater is installed as close to the internal oil cooler(heater)as possible warming the filter slightly before starting. I've seen 117°f water temperature drop below 100°f (lowest value displayed) on startup within a minute, fom the sub 0 oil pulling heat out. Point is both is best.
Run a Bunn quick thermos type coffee maker to heat and store hot water for the next go.

[oldtamiyaphile]

Originally Posted by gumby79

Run a Bunn quick thermos type coffee maker to heat and store hot water for the next go.

Not quite sure what you mean by this bit?

[gumby79]

This modded in
https://homecatalog.bunn.com/product...CUP/38300.0068 it has a 12-cup thermos in the back of it where is stores the hot water to make next pot of coffee in only 3 minutes after adding the cold water.