Question about mixing grades of oil

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Aug 24, 2002
Burlington, Ontario
I have to replace my oil pump on my 95 Golf, and although I'm sure it's not because of the oil grades I was using, I wanted to experiment with something. Currently, all I've ever used is a 5W30 or 10W30 depending on the time of year and always an OEM VW filter, which I understand is made either by Mann or Bosch. Question: Could I blend a 5W50 with a 5W30 to achieve a 5W40 oil grade in effect?? Problem with trying to buy a 5W40 is that no one except the VW dealers have this and it's $12 Cdn a litre!!! Advice, suggestions...
[Welcome!] fellow Ontarian! Just so you know, Walmarts here in Ontario sell 5w40, they have Havoline synthetic which is about $6.50 a liter, or you could go for the Delvac 1 5w40 which is $36 for a 4L jug. The Delvac 1 is an excellent oil, and can last for very long drain intervals. Delvac 1 is a diesel oil, but a lot of people on here use it in their gas engines. [ August 25, 2002, 08:55 AM: Message edited by: BOBISTHEOILGUY ]
Thanks for the welcome Patman! I got referred here from What kind of car do you drive? I'll check Wallymart next time for Delvac, that is exactly what I want.
I currently use a mixture of Mobil 1 15W-50 (1 qt.) with 3 qts 10W-30. I think when you mix you need to stay within the same brand. Welcome to the boards. [Cheers!]
Right, I figured that similar brands would be okay to mix, like Quaker State with Quaker State or Mobil 1 with Mobil 1 etc. I have a Wally Mart near me in Oakville so I will look there for it there. Thanks guys.
Originally posted by Al: I currently use a mixture of Mobil 1 15W-50 (1 qt.) with 3 qts 10W-30. I think when you mix you need to stay within the same brand.
You should NOT mix different multigrades of oil. That additives that give the multigrade characteristics are not always compatible, even within the same brands.
Mobil 1 xW-30 and 5W-50 are formulated to meet different specs. The -30 meets European ACEA spec A1 & A5, and the 5W-50 meets the A3 spec. As already said, 5W-40 Mobil Delvac 1 is the easy answer...or 0W-40 Mobil 1. Check a truckstop for the Delvac, or call a local Mobil distributor to find who retails it. Ken
Originally posted by Red Baron Golf: Thanks for the welcome Patman! I got referred here from What kind of car do you drive? I'll check Wallymart next time for Delvac, that is exactly what I want.
I drive a 95 Firebird Formula (350 LT1 engine) and my wife has a 2000 Civic. I just checked Walmart Square One and I was wrong about the price on Delvac 1. It's a bit cheaper than I thought, it's $34.96 for the 4L jug. Watch for those falling prices eh! [Big Grin]
Just a note about mixing oils, I mix oil wts and have done so for years. I mix about half 20w/50 with half 10w/30 after a vehicle gets about 50k miles on it. I normally do stick with one brand at a time, but even that has only been best effort over the years. Rando
When you mix oils, the negative effect would just basically be that you can't do the extended intervals, since additive clash (even between the same brand) would cause the TBN to drop faster. But if you're changing it out before 5-6k anyways, you should have no harm. I wouldn't mix viscosities and then try to go 10k plus though, not without oil analysis to show that the additives aren't clashing. There is this false rumor out there that mixing oil viscosities (or brands) will cause your engine to seize up, and this is probably coming from the days of early synthetics which did not mix well at all with other oils. The resulting mix would turn to gelatin. This simply does not happen anymore.
Interesting stuff! I typically change my oil out at 5000 km intervals, regardless of what oil is in there (even though it's been either a synth blend or a full synth). I realize I *could* go longer but I feel better just doing it. Plus it gives me something to do every once in awhile [Wink] I guess the whole reason I'm here on this board trying to learn more about oil (and this is obviously the place to do it!) is that I recently had an intermittent oil pressure light. Before you all go running screaming about engine wear or whatever, hear me out. It first happened around March or April, but I figured because I was driving the car really really hard, around a corner I figured I had just caught some air in the pump and it just got momentarily starved. Well happened again about 2 weeks ago. Diagnosed the switches and they were faulty. So I had both the high and low pressure switches replaced. Unfortunately, this didn't solve the problem. (Remember I'm driving a 95 Golf 2.0 with Mobil 1 full synth and an OEM VW filter). So I took the car into the dealer for a pressure test and sure enough, as the car gets warm, the pressure drops off. The tech estimates the pump is working at about 90% of what it should be. Nevertheless, I decided to park the car until the pump can be replaced, which is this Thursday. QUESTION!! Could the fact that I've been running a 10W30 or a 5W30 have ANYTHING to do with the failure of the oil pump? I'm kind of surprised that the pump is faulty...I've had other cars with much higher mileage and no pump promblems at all. (Like an 82 Reliant with 487k kms on it). The car started out life with 10W30 dino oil consistently changed at 5000 kms. Never used anything but a VW OEM filter. I ran Castrol GTX then Valvoline, if that matters. At about 50k kms, I switched to Valvoline synth blend, then switched over to Mobil 1 full synth at about 90k kms and haven't used anything else since.
Oil caused it? I don't think so. My guess is that the oil pump had larger than normal clearances and was leaking oil around the little pump gears, or leaking inside the housing. It could also be the oil pump has a defective internal oil pressure by-pass valve. I would not howver, mix grades. The VII's don't necessarily allow a linear relationship and taking the arithmetic average does not guarantee an oil of xx mixed with an oil of yy equals xx+yy/2 in viscosity.
Ok so when I mix the 10w/30 and the 20w/50 half and half maybe I actually get 16w/43... Not all 10w/30 oils have the exact same viscosity at the low and high reference temps either, the 20w/50 oils are in a range too. I am not trying to make a precision product by mixing oil wts, I just want oil that is about what a 15w/40 would be, and I always have plenty of 10w/30 and 20w/50 on hand. Every oil mfgr that I have called and asked the same question to has said the same thing, It is NOT EXACTLY a mathematical average of the 2 wts, but it is close enough....3000 miles later it comes out and more goes in...that is about as complicated as I let it get. Rando
I hear you Rando, It would be interesting to us anal types if you would send a virgin oil sample of your brew to Terry Dyson to see what the real starting viscosity would be.
hey Molecule, You send in a sample, I lost my job back in takes me a little longer to get those 3000 miles these days. I buy $.97 Havoline and Walmart filters, and drive 55mph just to save gas!! I'm sure the petro-distillers/crackers/blenders spend enough money just testing the major oil wts for the specs that the API/AUTO mfgrs require, they won't blow the money on the intermediate wts that they theoretically could make for folks like us, they can just extrapolate the data, just like we can ourselves.. seriously, I have never had one of them tell me that mixing wts is bad, they just tell me that they make a comparable wt to save me the trouble.. Maybe they would give me a job testing exotic wt oils for us here on these oil pages???? Rando
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