Oil light on when engine hot and idling

[maddave2000]

1972 1200 standard Beetle with 1600 engine (located in the UK).

Went for a longish drive yesterday in 25 degree C heat. Everything was running fine with engine temp from a VDO oil dipstick sender sat at 110 degrees C (230 f). When I was nearly home I stopped at some traffic lights and noticed the oil light was on, flickered quickly at first then on solidly. I thought the worst, but when revving the engine, it went out and would only come on when sat idling.

I realise this is low oil pressure, but what are the reasons for only happening at idle when hot and what are my options to rectify it? I've not had it happen before since owning the car since September last year and have completed some other long drives with no issues.

Engine oil is Valvoline VR1 Racing 20w-50 which was replaced just 600 miles ago. I did happen to top it up just before the drive, so not sure if that had any bearing on things. When I checked the oil yesterday it was still at the top mark of the dipstick. Engine is pretty much stock, with all fresh air hoses, genuine VW heat exchangers and tin correctly fitted.

Any advice would be great.

[viiking]

It is NOT abnormal for the oil light to flicker at idle and the engine is hot VW actually mentioned this in their documentation and said it wasn't of concern.

The oil pressure to initiate the light is so low and on the low end of the sender's capability that it only needs to be a little out of calibration and the light will remain on at idle.

Let's say the oil pressure light is on at idle at say 850 rpm, does the light go out when you raise the revs to say 1000? If so, I don't think you have a problem.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[viiking]

Here's the link to the 1972 Owner's Manual.

https://www.thesamba.com/vw/archives/manuals/72bug/1972_Beetle_Owners_Manual.pdf

If you go to Page 30 it states...

"AN OCCASIONAL FLICKERING OF THE OIL PRESSURE WARNING LIGHT WHEN IDLING AFTER A LONG HIGH SPEED TRIP IS NO CAUSE FOR CONCERN IF THE LIGHT GOES OUT ON ACCELERATION".
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[maddave2000]

Thanks, that's good to know.

It did go out on revving the engine, but it was flickering and then permanently on when idling. Does that count as flickering?

Also, doing some searching on the forum, is 110C/230F an ok temp for the oil? It seems this may be a bit high. I wasn't doing motorway/high way driving, just pootling around the country lanes at a max speed of 50 mph for an hour, so the engine wasn't being really stressed. Would using an oil with a lower grade help with increasing pressure, and lowering temp such as using a 10/30 oil, (as recommended on the oil sticky), rather than the 20/50 I'm using?

[bsairhead]

[mukluk]

A couple notes:

If your 1200 has a solid/unvented decklid, this can lead to above normal engine temps when a 1600 is installed. VW saw the need for more cooling airflow into the engine compartment with this larger engine and used a vented decklid on all 1600 equipped Bugs.

The stock VW oil pressure switch is designed to illuminate the warning lamp somewhere between 0.15-0.45 bar (2.2-6.5psi). It's been noted that some aftermarket switches cause the lamp to come on at higher pressure than stock spec, so that's something to be aware of -- you may be getting a false indication.
_________________
1960 Ragtop w/Semaphores "Inga"

[baldessariclan]

[maddave2000]

Thanks all. Interesting, some definite food for thought.

The previous owner of the car had added additional vent holes in the deck lid under the number plate, so it does have some further ventilation. It does make you wonder why they felt they needed to do that though... I used to drive a 1200 with a 1600 TP when I was a teenager, with no additional vent holes and never experienced the engine being too hot, or the oil light ever coming on, so this is a little unusual for me for this car.

I've taken the action to swap out the oil for 10/40, and also to fit an oil pressure gauge. I think I'll see if that helps with temps, but also allow me to monitor the oil pressure too. I might fit the latter before dumping the current oil and that should allow me to compare the difference in pressure to the thinner oil.

[Cusser]

[Starbucket]

You may want to check your timing as too much advance will cause over heating.

[viiking]

The discussion of oil temperature of a running engine is a complex science in itself. It is quite difficult for the layperson to determine what is best.

One of the things that people possibly are not aware of is that "oils ain't oils".

The specification of Product A's 10W50 is not necessarily the same as Product B's. Yes at two certain temperatures they may be as per the Society of Automotive Engineers (SAE) method but in between they may be different.

I would encourage everyone to look up the SAE method and see how it is actually measured and how the W number viscosity is determined.

A third measurement the "High temperature/high shear" viscosity also has to be met. This is the viscosity that must be achieved in a simulation where the temperature and pressure between engine parts under extreme stress at 150 degrees C must be maintained. If the viscosity of the oil is too low at this temperature then the oil film between the parts may be insufficient to provide lubrication leading to failure. Read spun bearing for example.

Also what is really important is the "Heat Capacity" of the oil. That is depending on its composition, different oils of the same viscosity may require more heat to raise the temperature of oil by one degree than others. That is, oil of the same grade may in fact run hotter than another company's same grade for the same heat input.

So in short, if you really want to know if one oil is better than others, you need to look at the technical data sheets of the manufacturers not just the 10W50 number.

The problem however will always be that all of the scientific data will have been done to a standard and controllable. The biggest problem we have is that people comment that when I run my car on oil X it runs cooler than oil Y. In general they use "I reckons", know nothing tangible about the amount of heat being produced by the engine, temperature and humidity of the day, haven't got a calibrated and accurate measurement of temperature, drive on different roads and altitudes etc.

The last comment is not to insult people or suggest that they don't see a difference but very often the conditions that one person see are not the same as another's and therefore not transferrable. Even from day to day.

Finally using "racing oils" in daily drivers may not necessarily provide the right protection for normal cars. Racing cars rarely need excessive cold start conditions and have been specifically formulated for very high temperatures and shear loadings. But the specifications would be interesting to read.
_________________
1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[Buggeee]

The vw oil cooler is accessed by the lower oil pressure of hot oil. Because of this design, the higher pressure of thicker oil will push down the spring longer, delaying access to the oil cooler. I use VR1 10W30 in my beetle, which calls for that lighter weight. I use VR1 20Ww50 in my 88 Vanagon, which calls for that heavier weight. The springs are designed with a particular weight oil in mind, expecting the thinning to equate with a specific temperature of warming, allowing access to the oil cooler at a specific range of tempurature. A high pressure oil pump interjects the same variable, delaying access to the oil cooler. Basically the higher pressure tricks the oil spring into thinking the engine is colder than it is, resulting in it running hotter.

The flickering light is something that I experience as well under the conditions described. The steady on at idle is something I might see in a hot summer day after a long run on the highway, but is not as common to me.

Also, some replacement oil pressure sending units, particularly the dual pole units that also feed a pressure gauge in addition to the light, are calibrated with a bottom range that is like 7 psi instead of the 3 psi of a stock one, so they flicker and light up even more at idle.

Just some random thoughts, enjoy the car
_________________
Big Time 1988 Vanagon Westy
Release the Krankenwagen! 1966 Sportsmobile Camper
Dr. Kompressor 72 Super Duper
61 Turkis Pile (adopted out)

[Cusser]