The V8 Owners Forum -

Hi,

I've got a Mazda MX5 with a 3.5 modified Rover V8 which sits pretty comfortably in the engine bay. It benefits from a huge custom radiator and a bonnet scoop. It's generally quite a cool running car, even in traffic it takes a while for the fan to be needed.

This week due to time I dropped it off at the local garage and they put in semi synthetic 10w40. My normal oil is 20w50, any premium type. As soon as the oil was changed I could feel the heat from the engine bay, way warmer than normal. Oil pressure seems roughly the same, coolant normal but the vents on the dash were very warm.

Anyway I swapped the oil back to 20w50 this morning and what a difference. When I took the 10w40 it looked almost like water, I guess there simply isn't enough thickness to pump the oil efficiently.

My SD1 EFI specifies 10/40 in the UK. No idea why the oil grade would make a difference to the heat from the engine - if anything I'd expect a thicker oil to be worse, as it wastes more energy.

I guess there could be many reasons for this phenomenon?
I have always used 20/50 mineral oil in my Rover V8's be they the original low comp 1975 unit in the MGB right up to the 4.6 race engines. When I tweaked the last Rover out to 4.9 litres I did use 15/40 mineral oil to see how it would perform. It was ok for me for racing.

A friend of mine is an analytical oil chemist and I'm sure he would be able to come up with a long explanation about why this could have happened. But the long story short is : If the change back to 20/50 solved your problem then stick with it and have fun

Perry

Interesting. My engine came from a TVR Griffiths 500 donor and it specified Mobile 1 on an engine plate. I thus used this and have noticed that after a short time at motorway speeds my oil temp gets high - 20 degrees above 'normal side road cruising & non-motoring driving'. So much so that I am really limited to 65mph for anything other than short bursts as my water temp increases to probably close to 110 presumably due to the hot oil.

A couple of years ago the recommended listing on Mobil's web site was Mobil 1 Extended Life 0W-40W. Now in Feb 2016 the oil for my engine is now recommended as Mobil 1 Peak Life 5W-50. Obviously fully synthetic. That's what I use.

I've put some cowling around the radiator to help with cooling but not yet had a chance to try this out on motorways. I suspect that the oil will get hot as before and I believe that that is what is making my engine hot.

So, perhaps I should change to quality 20/50?

20W50 is too heavy for a good engine - should only be used in worn out engines.

I normally use 10w40.

garrycol wrote:20W50 is too heavy for a good engine - should only be used in worn out engines.

I normally use 10w40.

I'd agree, given this was specified by BL latterly anyway.
But having been around a lot of high mileage RV8s, the more important thing is the additive package to prevent cam wear. They don't normally suffer bearing problems which would be associated with too low oil pressure.

DaveEFI wrote:

garrycol wrote:20W50 is too heavy for a good engine - should only be used in worn out engines.

I normally use 10w40.

I'd agree, given this was specified by BL latterly anyway.
But having been around a lot of high mileage RV8s, the more important thing is the additive package to prevent cam wear. They don't normally suffer bearing problems which would be associated with too low oil pressure.

I agree Dave!
20/50 is used in many classic car engines 4 and 8 cylinder? The additive package in the oil OR dropped in separately is the key to engine life, along with regular oil changes?
I think that many of us rebuild our 40 year old V8's to much better standards and tolerances than they came from the factory with

Perry

mgbv8 wrote:The additive package in the oil OR dropped in separately is the key to engine life, along with regular oil changes?

Yes, I agree 20/50 is probably not correct for my engine. What additive package do people suggest, then (but I thought most quality oil brands have them added anyway).

richardpope50 wrote:

mgbv8 wrote:The additive package in the oil OR dropped in separately is the key to engine life, along with regular oil changes?

Yes, I agree 20/50 is probably not correct for my engine. What additive package do people suggest, then (but I thought most quality oil brands have them added anyway).

I've always the hi zinc oil additive that Real Steel sell.

Now I was always told by my friends with air cooled Porches that they used 20/50 Dino oil as it was far better at cooling the engine than the modern synthetic oils, if that is correct it could explain the issues that you were getting with the higher temperatures.

According to what I've read, the important additive is ZDDP. It's not found in most modern oils as it's not compatible with catalytic converters. But is the best additive by far for the high tappet/cam loads on a pushrod engine - the load on an ohc design is very much lower.

A Google of '20/50 Dino oil' seems to show them as the Classic oils as per Castrol vintage range and seems they are used a lot in motorbike engines too.

ZDDP additive is also widely available but it too is classed as a Classic oil additive.

Is this correct?

I'm now thinking a quality 10/40 is the best one to try.

I'm using a quality 10w40 and I get no overheating issues cruising on the motorway (In my Dax Rush) and I have an intercooler blocking half my rad. I do have a winged sump which hangs down a little which may help to temperatures at speed?
I haven't used it in anger at speed for prolonged time yet see i'll have to see if I need to add cowling.

Tom.

Having managed a good run including about 10 miles dual carriage way (A3) @ 70mph, my cooling has not improved with the cowling in place. Despite my rad being 70mm thick and designed for maximum cooling, there's still a problem.

In the 10 miles at 70, engine oil increased by 15 degrees and water temp hovered at 110 degrees (and dual speed fan at max as well). Drops to around 95 degrees when 'normal'.

10/40 it is, then.

Can the air that came in through the radiator easily get out of the engine bay?

Rule of thumb you need 1/3 of the radiator surface opening in front of the rad (your cowling in this case) and 2/3 the surface area for air after the rad.

So unless you have gills, open under the car etc can the air get out?

If not you will not get cool

Ian