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Imp oil

Date: Wed, 2 Jun 1999 17:35:36 -0400
From: David Oakes
Subject: [imps] Imp oil

>I would very much like to know what oil Ian Carter recommended

Ian was very definite about the type of oil I should use, and even wrote it down for me - I have his note here. It says Motaquip Diesel oil - 15W/40 Winter. API CD/SE. I filled my engine up with oil for the first time last weekend and used Castrol Diesel 15W/40. He told me that a standard diesel engine has to cope with much higher forces than all but the most highly tuned petrol engines. However, I'm a bit concerned as no-one else seems to know anything about using diesel oil in high performance imp engines.

I'll see what happens!


From: Gary Henderson
Date: Thu, 3 Jun 1999 10:24:19 +1200
Subject: Re: [imps] Imp oil

How does diesel-grade lube like the shear-rate of an engine that does 8000 rpm? Nick?


From: Andrew w MacFadyen
Date: Thu, 3 Jun 1999 09:25:32 +0100
Subject: Re: [imps] Imp oil

Time to nail a few misconceptions.
Yes, loads generated by the pistons are higher in diesel engines (but remember also they have bigger bearings and rotate at lower RPM), but comparing the film strength modern high quality oils for petrol engines with equivalent quality diesel oils you will find them exactly the same. It might be different at the bottom end of the market where 20w/50 made from recycled feed stock sells for 3 quid a gallon.

The traditional difference between petrol and diesel engine oils is the amount of detergent additive they contain. Up to about 1960 petrol oils had no or very little detergent in them. When detergent oils were initially introduced some older engines ran bearings because of the build up of black carbon sludge that was clinging to the engine internals was lossened and carried away by the oil only to block the oil ways or filter. This was one reason for the bearing problems suffered by early pre-cross flow Ford Kent engines. However since then every engine petrol or diesel has been filled with detergent oil since new and the problem has almost disapeared.
The volume of detergent additive in quality (petrol engine) oils has steadily increased to cope with the more difficult combustion conditions and extended service intervals found on modern cars. Some of you may remember the black sludge scare in the early 80s.

Look at the specification of most normal engine oils (petrol or diesel) you will also find they meet (for example) SF and CD specifications --- indicating they are suitable for both Petrol and Diesel units.
However specialist diesel oils have additional detergent additive and anti-corrosion additive to allow an additional safety margin in the event of a missed oil change.

Using a specialist diesel engine oil in a new or overhauled petrol engine should cause no problems however using it in an engine which is very dirty inside brings the risk of blocked oil ways.

When buying an engine oil look at the specfication it meets -- the latter in the alphabet the second letter is the higher the specification -- for example cheaper oils might meet the SE specification for petrol engines SE was an early 80s specification introduced in response to the black sludge problem and has been superceded several times whereas the container of Duckhams sitting in my garage proudly proclaims it meets SJ specification.
The difference between these specifications doesn't mean a great deal - mainly refering to the amount of detergent, anti-varnish and anti-corrosion additives in the oil. However they are a fairly good guide to how on the ball the manufacturer is.

In terms of rubbing speeds diesel engines are not too disimilar to normal petrol engines; although on diesels the RPM is lower the crank journal are of a much larger diametre.

Incidentally at least one major lubricant producer sold exactly the same oil under different names and vastly different prices to the high street market and mixed fleet/agricultural users.


From: Tim Morgan
Date: Thu, 3 Jun 1999 10:59:10 +0100
Subject: Re: [imps] Imp oil

Hi Andy,

I'm not going to argue one point of this, as you obviously seem to know far more than me.

One point I'll make, concerning the 'cheaper' oils.....

If you don't mind changing the oil and filter at lower intervals, there is no reason why you can't use the cheap £2.99 oils you get at the Motor Factors. To be honest, I change my oil & filter possibly a little prematurely at 3000 mile intervals, and am fairly broke at the moment.
Therefore, if it is a choice of using a 3000 mile+ old oil & filter or using a cheap £2.99 oil and fresh filter I know what I'd choose.

Modern oils are all very well; Andy makes the point that they are designed for longevity due to the increased periods between changes in modern cars, but if you are changing the oil far more regularly than that, do you really need oil that costs the earth?

There is a lot of Y-Fronts spoken about oils these days - bear in mind the quality of the oil the average motorist used in the 60s & 70s, and those engines are still in the back of YOUR cars including some of the higher performance cars (mine included). Synthetic this, and High Performance that... sorry, but after studying the psychology of marketing that sounds like money in the bank for someone.

I'm sure that there are properties in some of these oils that are useful to those who have Turbos, fuel injection, engine management and 12,000 mile service intervals on their GTis etc, but the Imp engine is an old design, and you aren't going to gain much from spending three times as much as me on oil.

One final point - Ian Carter seemed to change his mind regularly about engine oil. He's told David O to use Diesil oil in his 998, he told a mate of mine to use Castrol GTX (too thin) in his 930, he told another friend to use Duckhams Hypergrade in his 998 - perhaps he didn't believe in the marketing hype too :-)


From: Andrew w MacFadyen
Date: Thu, 3 Jun 1999 19:38:36 +0100
Subject: Re: [imps] Imp oil

Yes, for a non tuned engine or a high mileage one a cheap oil changed often is a good thing. In any case, most budget oils meet at least SE spec which was just brought out circa 1984. But for a tuned unit I will always favour synthetics --- Castrol RS.
Incidentally I bought 6 litres of Duckhams Hypergrade for 11 pounds last week.


From: Robin Human
Date: Thu, 3 Jun 1999 20:59:22 +0100
Subject: Re: [imps] Imp oil

I had extensive discussions with Ian Carter on the subject of oil and he would always recommend Duckhams Q. He warned me that under no circumstances should I use Castrol GTX as the molybdenum powder had a tendancy to block small oil galleries with catastrophic results.

As for 'diesel' oils I know that they contain additives to neutralise the acids that diesel engines produce and additional detergents.


From: Alan
Date: Fri, 4 Jun 1999 09:07:20 +0100
Subject: Re: [imps] Imp oil

Robin, et al... let's keep things in perspective here... Ian Carter built mostly highly-tuned engines, so for the most of us, all this high-tech stuff is irrelevant... as long as the SAE rating is as Rootes/Chrysler intended, and conforms to good current specs., then it's no big deal.

I fitted a 998 to my Sunbeam about 1985, and it's never been opened-up since, having been used for both normal driving and sprints/hillclimbs... all the time I've used GTX !
No catastrophes with me... so, Ian Carter was wrong, shock-horror?!!

Dundee United will have won the SPL before you have problems with molybdenum powder !!!


From: Andrew w MacFadyen
Date: Fri, 4 Jun 1999 13:21:33 +0100
Subject: Re: [imps] Imp oil

I had great faith in GTX in the seventies until I raced Imps, after that Valvolene and Duckhams got my vote. Now in the late 90s modern GTX seems much better than it was 20 years back.


From: Robin
Date: Fri, 4 Jun 1999 21:15:21 +0100
Subject: Re: [imps] Imp oil

Ian had trouble with the racing version of GTX when he was paid to put it in his engines. The powder was found to block the oilways with catastrophic results. With this in mind Ian advised customers not to use GTX, just in case.

Castrol were not interested in the problem with the oilways and legal action commenced, I am not sure of the outcome. I will investigate further and report back.

I realise that Ian built predominantly racing engines but the principles of good lubrication apply to all engines. an an oil be too good for your imp engine?


From: Nickcleak@aol.com
Date: Fri, 4 Jun 1999 16:48:15 EDT
Subject: Re: [imps] Imp oil

> all the time I've used GTX !
> No catastrophes with me.......

well, i have used GTX for 30 years too .. only road use though
However Valvolene 20 / 50 seems one of the best for everyday use ..



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