Engine pre-heaters

[phuston]

You will see small Rotax engined aircraft sitting round clubhouses for minutes with their engines running at 2000rpm. They are waiting for the oil temperature to reach 50 degrees C before using full throttle for take off and climb out. Treated this way the engines will last for at least 3000 hours. There does seem to be something to the idea of getting the oil within it's operating range before using all the engine's power, very few road cars will ever use full throttle and maximum rpm (when under load) from cold.

How many of our race cars have oil temperature gauges?

I have never had an oil temperature gauge on a car, and would have only looked at the top of the scale if I had one.

[samier]

Good point, but I have always run my cars for about 10 mins until the oil gets to normal operating temp, but also making sure the water does not boil over. I would switch it off at around 75 degrees water temp.

[tristancliffe]

I have been trying to figure this out, I have seen a few cars if on stands, you can freely rotate the wheels with out any effort at all, while some you need you put a bit of effort. Not sure exactly what they are doing to reduce the friction. Are you saying they run no oil? or maybe a different grade or engine oil?

some teams runs with no gearbox oil at all, and some even remove the grease from wheel bearings and tripode joints to reduce drag. Of course, this only works if you can afford to replace those items every session/race/meeting as applicable. I wouldn't recommend that most Mono people try it.

[tristancliffe]

Good point, but I have always run my cars for about 10 mins until the oil gets to normal operating temp, but also making sure the water does not boil over. I would switch it off at around 75 degrees water temp.

Without driving the car reasonably hard, the engine oil temp will not reach half of normal operating temp. 30 degrees max really.

[samier]

I guess the other thing is as we dont go out of the pitlane and around thw whole lap to form on the grid, we lose 1 lap to put enough load into..so all the warming up is done on the actual green flag lap.

Out of interest what grade oils are people using? Surely something like a 15w50 would take longer to heat up than a 10w50?

[Tailgate]

I'm in the Dermot camp...mostly production engines with more forgiving tolerances...I'm not saying it shouldn't be warmed up but a good fast idle for as long as the cooling system can stand it then shut it down to let it heat soak, I would have thought doing this 30 mins before heading off to the assembly should get sufficient heat into everything ?

In my opinion a more worthwhile pre-start activity would be removing the plugs and spinning the engine over to get the oil pressure up, this ensure all the oil galleries are charged and all the components get an oil supply, removing the plugs also eases the load on the starter/battery considerably.

Pre-heating the oil is no bad thing but it seems like a lot of effort for not a lot of gain...but I may be wrong, wouldn't be the first time !

[tristancliffe]

Heatsoak has no effect on oil temps if the oil tank is separate from the engine - in a Dallara the tank is in the gearbox casing, a long way from the warm engine. On a wetsump engine heatsoak works quite well.

Building the oil pressure by cranking is pointless really, unless the engine hasn't run for months or has only just been rebuilt. As our engines are run fairly regularly, we gain nothing by spinning the engine on the starter.

Most race engines don't have pressure relief valves on the scavenging side of the system, so cold oil is forced around at high pressures until it is warmed. It's quite common for engines to burst oil coolers and filters on scavenge systems if the oil is cold, or you ask a lot of the pump, or the drive mechanism for the pump (belt, chain, shaft).

Production engines designed for cold climates have additional protection - relief valves, clutches on pumps, and a thinner oil specification.

Preheating the oil somehow (heatsoak if possible, external heater if not) will massively reduce the strain on parts of the engine.

[guilleracing]

Just thought I would mention my plan to use a little 12v heater for the oil tank. ( When it arrives.)

The operation for this would be as follows.

Open filler lid, put the heating element into the oil in the tank. (It is about the size of a small bread knife.
Battery connections would be with crocodile clips or similar, inline switch from B+Q home lighting range.)

Turn the heater on and leave it until the temperature gets to about 50 degrees and then turn it off.

Remove and wipe with cloth, close filler lid.

In the intervening time you could do all the other things you need to do, tyre pressures etc.
(consumption of Bacon Rolls optional!)

Some consideration should be given to the temperature of the oil resting in the sump and pipework, but in principal this is how I imagine it would be operated.

[samier]

Just a thought, if people are concerned about getting the engine oil heated up, why not use a thinner oil at cold weight, instead of using a 10w or a 15w, perhaps a 5w? That should circulate a lot faster and heat up a lot quicker and reduce wear during the first few minutes. Maybe I am wrong here.. Ok the 0W20 is probably an overkill and more suited to those who rebuild their engines very often. Surely a 5w40 would be a better option? Maybe some of the XE engines with a higher ring /shell clearences would need a thicker oil, but Zetecs, Toyota engines could use a thinner oil?

I have been looking at the oils by Motul:

Motul 300V 0W20

PERFORMANCES
STANDARDS Above existing standards.
Reference team Toyota Racing Development, Japan GT – Graff Racing, Formula Renault
(open wheel cars, single brand race)

PROPERTIES
Viscosity grade SAE J 300 0W-20
Density at 15°C (59°F) ASTM D1298 0.857
Viscosity at 100°C (212°F) ASTM D445 8.0 mm²/s
Viscosity at 40°C (104°F) ASTM D445 40.1 mm²/s
Viscosity index ASTM D2270 177
HTHS viscosity at 150°C (302°F) ASTM D4741 2.68 mPa.s
Pour point ASTM D97 -39°C / -38°F
Flash point ASTM D92 220°C / 428°F
TBN ASTM D 2896 11.3 mg KOH/g


Motul 300V 5W30

PERFORMANCES
STANDARDS Above existing standards.
Reference team NISMO NISSAN, Japan GT – Coloni Motorsport, Formula 3 (open wheel
cars)

PROPERTIES
Viscosity grade SAE J 300 5W-30
Density at 15°C (59°F) ASTM D1298 0.871
Viscosity at 100°C (212°F) ASTM D445 11 mm²/s
Viscosity at 40°C (104°F) ASTM D445 65 mm²/s
Viscosity index ASTM D2270 162
HTHS viscosity at150°C (302°F) ASTM D4741 3.61 mPa.s
Pour point ASTM D97 -36°C / -33°F
Flash point ASTM D92 218°C / 424°F
TBN ASTM D 2896 11.3 mg KOH/g


Motul 300V 5W40

PERFORMANCES
STANDARDS Above existing standards.
Reference team SUBARU WRT, World Rally championship –
Graff Racing, Formula Renault (open wheel cars, single brand race)

PROPERTIES
Viscosity grade SAE J 300 5W-40
Density at 15°C (59°F) ASTM D1298 0.905
Viscosity at100°C (212°F) ASTM D445 13.8 mm²/s
Viscosity at 40°C (104°F) ASTM D445 80.8 mm²/s
Viscosity Index ASTM D2270 176
HTHS viscosity at150°C (302°F) ASTM D4741 4.51 mPa.s
Pour point ASTM D97 -36°C / -33°F
Flash point ASTM D92 216°C / 420°F
TBN ASTM D 2896 10.9 mg KOH/g


Motul 300V 10W40

PERFORMANCES
STANDARDS Above existing standards.
Reference team SUBARU STI, GT Japan.

PROPERTIES
Viscosity grade SAE J 300 10W-40
Density at 15°C (59°F) ASTM D1298 0.880
Viscosity at 100°C (212°F) ASTM D445 14 mm²/s
Viscosity at 40°C (104°F) ASTM D445 89.5 mm²/s
Viscosity index ASTM D2270 161
HTHS viscosity à150°C (302°F) ASTM D4741 4.19 mPa.s
Pour point ASTM D97 -36°C / -33°F
Flash point ASTM D92 226°C / 438°F
TBN ASTM D 2896 11.7 mg KOH/g

[tombrown]

I had a car once which had a kettle element built into the bottom of the dry sump tank, with the normal kettle plug on the outside.

Looked a neat idea, but I cant say I ever used it!

Tom

[samier]

Now that is a good idea!

[tristancliffe]

I am posting this on behalf of Martin. He has too much sense to register and post on a forum when his life doesn't depend on it. I am more foolish (you don't look surprised), so here I am.

Martin does not claim to know everything about oil. It is quite possible he is incorrect, although this is unlikely given past performances. It is fairly unlikely that copy-pasting some random information from website of an oil distributor (I won't use the word manufacturer, as I doubt Motul actually manufacture the oil, but just add stuff to the oil they buy, which has probably already had stuff added to it as well, etc.) that you don't understand will help anyone, even more so if you don't understand the problem in the first place.

Martin:

Oil


Oil has two functions:- to lubricate the engine and to cool the engine.

The first one is complex because you have quite disparate regimes. A plain bearing, a ball bearing, a piston, a piston ring and a cam follower ideally would like different lubricants. Clearly this is impractical, so that favourite word of the engineer, COMPROMISE, is the key to it,

The highest loaded area in any engine is the cam to cam follower interface. If the oil is suitable for this it will stand a good chance of coping with anything else that a well designed engine in good condition being operated in a sensible manner will cope with it. Zinc dithiophosphate additives are necessary. Unfortunately these are being reduced or eliminated to help with emissions, so modern oils are getting worse in this respect.

Main bearings or rod bearings are easy to lubricate (but much less easy to design). Oil pressure is generated by the hydrodynamic effect of the oil film and has little to do with the oil pump. Oil pressure is necessary to persuade the oil into the crankshaft main bearings against the effect of centripetal force. For a 7000 RPM engine I think that only about 35 psi is necessary. This could be almost zero on an end feed crankshaft.

Oil pressure is not controlled by the oil pump, but by the bearing clearances. Think of putting your thumb over a tap. There is no pressure until the flow is almost completely reduced.

The sheering effect of the oil generates head and there has to be enough flow to carry away this heat. An aluminium engine relies on oil to cool it much more than an iron engine.

The designer has to juggle oil pump specifications with bearing clearances.

Most damage to an engine occurs in the first few seconds after a start up before oil is circulating. The oil pressure is typically measured on the pump out put, or the main oil gallery. It can take much longer for the oil to start circulating in remote areas like head or cam oil galleries. This is worst with thick oils and cold ambients. Cranking the engine to build pressure on the starter with the plug leads off barely reduces this.

An oil has to be thin enough to circulate quickly in cold climates, yet thick enough to keep bearings separated. Clearly a duty conflict. In ancient times single viscosity oils were hopeless. Multi grades made a huge difference. Contrary to popular opinion they get thinner with increasing temperatures, but not as quickly as a straight oil.

Cold start conditions can generate enormous oil pressures that even the pressure relief valve cannot control. Burst oil filters and oil coolers are not unknown. Dry sump systems are much worse because there is seldom a relief valve on the scavenge circuit. Slipping clutches are sometimes employed to mitigate this.

Luckily racing cars are only operated in a very narrow window of ambient temperatures but I expect winter rally cars have a hard time coping. Don’t forget that aluminium has a high coefficient of expansion. Bearing clearances at operating temperatures can reduce to such an extent that the engine is impossible to crank. Planes or trucks operating in arctic conditions sometimes never stop the engines as they cannot be restarted.

[samier]

Very good article.

Martin mentions about cold start, thicker oils being harsh during start up. In our colder climate, surely a 0w or a 5w oil would be better than say a 10w or a 15w oil?

Regarding the hot weight, ie 30, 40, 50 something like a 40 should offer adequate protection at 100 degrees? I know modern engines usually run a 30 weight such as Duratecs etc, I am guessing this is due to narrower bearing anf ring tollerances?

[tristancliffe]

Very good article.

Martin mentions about cold start, thicker oils being harsh during start up. In our colder climate, surely a 0w or a 5w oil would be better than say a 10w or a 15w oil?

Regarding the hot weight, ie 30, 40, 50 something like a 40 should offer adequate protection at 100 degrees? I know modern engines usually run a 30 weight such as Duratecs etc, I am guessing this is due to narrower bearing anf ring tollerances?

Our climate isn't considered cold, especially during the racing season.

Modern oils retain their ability to lubricate and generate hydrodynamic films well into the 130° range.

Thinner oils are used to promote economy - this would obviously also promote power if that's what you're after (and in racing, it is), but at the expense of lubrication. Then modern cars are given silly service intervals that aren't actually good for them... it's a wonder that they last as long as they do.

And do try not to use the term weight with oils. Sure, they all weigh something (mass under the influence of gravity), but the term weight when discussing viscosity is a horrid Americanism made popular by stupid people.

[Dermot Healy]

"........Dry sump systems are much worse because there is seldom a relief valve on the scavenge circuit. Slipping clutches are sometimes employed to mitigate this....."

I had hoped to keep clear of this... however

(a) i'm not sure i follow the quote above as surely the scavenge circuit consists of one bit sucking (ooooooh what fun) and another bit just squirting (aaaarrrrgh) the oil through largish pipework into the tank. Can't really see how under any circumstances there could be a significant build up of pressure in a scavenge circuit.....hence no need for relief valve..and i'd be interested in the examples of the slipping clutches you talk of 'cos i've never encountered any.

(b) Also, the issue of appropriate oils in production derived engines perhaps also needs to take into consideration the tastes of hydraulic tappets which can be fussy about what they are fed & perhaps might pump up if they find it too indigestible.