How do you determine the proper HTHS rated oil?

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I was simply curious, had this discussion on a Jaguar board. Another member suggested a hths of 3.5-4.0 for the v8 motors.

Ive got several different types of engines, ranging from MG 4 cylinders to Jag v12s and Volvo 5 cylinders. I do tend to split hairs and it seems these numbers are not shared by manufactures.

It was also mentioned that there are no oils which a rating above 4.0, I wasnt sure what he meant by that?
 
Generally speaking, look at what a manufacturer specifies, and see what the typical HTHS of that oil would be. If something is specifying an ILSAC 30, it's almost certainly going to have an HTHS of 3.1 +/- 0.1. Something calling for an A3/B4 or CJ-4 rated oil is looking for 3.5 or higher. And, there are many oils with an HTHS higher than 4.0. Red Line's 20w-50 has an HTHS of 6.1.
 
Ok thanks!

The reason why I was asking was because of the MG's odd oil recommendations. They used to recommend 10w/30, but 20w/50 was sort the national standard in England because of the popularity of the Austin Cooper shared sump engine. There were some reports of increased bore wear in these engines where 20/50 was used. Still a majority of MG guys use that grade. I used 10/30 before I knew of this, and after I switched to what everyone was using. A popular MG club member told me about how MG designed their motors from Moog tractor motors. 20/50 was added to tractor engines in case the operator walked away, and the water overheated, maybe a thick oil film would save the engine. I personally do not idle engines, only doing so in traffic, I warm the engine by driving slowly.

However, 20/50 made a noticeable difference in engine performance, its as if 10 hp was taken away. Now, I think this would cause a major oil overheating problem, so now I'm thinking about going back to 10/30. Maybe I should add an oil temp and pressure gauge to compare.Future post coming soon.
 
Originally Posted By: tig1
How do you determine HTHS? Use the wt oil the manufacture recommends.

As I said, it's fairly simple to make a reasonable estimate of what the manufacturer has in mind, based upon their recommendations. When Ford is recommending a 5w-20, you know it's an ILSAC 5w-20, and not a Red Line 5w-20, which will be significantly different based upon HTHS. When GM calls for a 5w-30 dexos1, you know that a 5w-30 A3/B4 will be significantly thicker at operating temperatures.

Look at the trouble VW/Audi service departments have gotten into over the years by not being able to understand the difference between a 0w-30 or 5w-30 ILSAC versus a 0w-30 or 5w-30 A3/B4.

FordCapriDriver: There probably are some racing oils with higher HTHS that you could track down, but that Red Line 20w-50's HTHS of 6.1 is pretty high.

79sunrunner: Depending upon application, one has to be careful, particularly when looking at some older engines. An engine that specified a 10w-30 back in the 1970s wasn't necessarily expecting one with an HTHS of 3.1. It may not be a problem. However, a lot of engines back in those days specified a range of viscosities, so it's worth paying attention to that.

It's much easier to estimate what the OEM had in mind nowadays, when they specify one grade, and even with them having a chart from other parts of the world, with SAE J300 having been tightened up on the HTHS front. For the MG, if it were me, I'd probably consider a 10w-30 HDEO, rather than a 10w-30 PCMO.
 
Garak,
Most of that is smoke and mirrors for internet argument. Almost no one (percentage wise)uses Red Line oil. We all know that most 5-20,5-30 SN oils recommended by a manufacturer will have a comparable HTHS.
 
Ahh Garak is right here. There is a sizeable difference between a ILSAC GF-5/ Dexos approved oil and an ACEA A3B4 oil in terms of operating viscosity. That's why Dexos has the much lower HTHS is for the fuel economy difference. Nothing wrong with Dexos approved oils or ILSAC GF-5 ones.
 
Originally Posted By: bbhero
Ahh Garak is right here. There is a sizeable difference between a ILSAC GF-5/ Dexos approved oil and an ACEA A3B4 oil in terms of operating viscosity. That's why Dexos has the much lower HTHS is for the fuel economy difference. Nothing wrong with Dexos approved oils or ILSAC GF-5 ones.


How much difference? 3.? compared to 3.? for 5-30 oils.
 
Hi,
79sunrunner - the "A" series Austin-Morris (BMC) engine ran very well on SAE20W-20 (Castrolite), SAE30 (Castrol XL) and 10W-30 lubricants when new - depending on Climate!

The 20W-50 lubricant was developed in '58/59 by Duckhams (Q2050) especially for the shared lubrication requirement in the Mini. Castrol followed with their 20W-50 soon after in 1959. It sadly became a "default" lubricant viscosity for all and sundry!!!

Depending on your Climate I would use a 10W-30

As to determining the correct HTHS viscosity some long term posters have offered great comment. In reality only the OEM knows the real requirement of the engine
 
Originally Posted By: tig1

How much difference? 3.? compared to 3.? for 5-30 oils.


Typically 2.9-3.1 for GF5 vs 3.5-3.6 for A3/B4. The lower number is the minimum set by the specification.

Ed
 
Originally Posted By: Doug Hillary
Hi,
the "A" series Austin-Morris (BMC) engine ran very well on SAE20W-20 (Castrolite), SAE30 (Castrol XL) and 10W-30 lubricants when new - depending on Climate!


I remember we used to use Castrolite and XL, but couldn't remember what viscosity they were. Our Caltex oils were of similar grades. We didn't use any special oils more Minis, or any other of the BMC fwd cars...but they were on 1,000ml oil changes anyway.
 
Originally Posted By: edhackett
Originally Posted By: tig1

How much difference? 3.? compared to 3.? for 5-30 oils.


Typically 2.9-3.1 for GF5 vs 3.5-3.6 for A3/B4. The lower number is the minimum set by the specification.

Ed


As I know it won't sink in, 3.6 versus 3.1 is 15+%...it's significant
 
Originally Posted By: tig1
Most of that is smoke and mirrors for internet argument. Almost no one (percentage wise)uses Red Line oil. We all know that most 5-20,5-30 SN oils recommended by a manufacturer will have a comparable HTHS.

It's true that Red Line is a niche product. And yes, that was my point, we know almost exactly what HTHS we're getting with an ordinary SN/GF-5 30 or 20. And, the same applies with an A3/B4 30 grade, which will be thicker at operating temperatures by at least 10%, and that's comparing the thickest 10w-30 ILSAC I can think of versus a bare minimum 3.5 HTHS A3/B4. HTHS winds up being part of a lot of specifications.
 
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