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Triumph TR6 - Carb Dashpot Oil

Over the winter I'd been pretty happy using 10W-40 in the dashpots. The acceleration was really good on the triple Z-S setup.

Then on the first really warm day I went downtown and got into some traffic. When it finally cleared up, the acceleration was definity off some. I attribute it to the carbs heating up and the lower viscosity of the oil at those conditions. It took about 20 minutes of driving before it ran right again.

So then I decided to experiment (again). This time I started measuring the dashpot oil temp just after a drive, and looked at oil viscosities at different temperatures (a good on is found at

First off, under normal conditions on a 85 deg F (30C) day, the oil was 105 deg F. It's probably not unreasonable to figure it reaches 125F on a really hot day, or with traffic. so I used those as the viscosity "bounds"

The 10W-40 was replaced with straight SAE 40 to see how it would handle warm conditions. It only lasted a weekend - it's much too thick for my set-up and gave poor acceleration even at 105 deg F. The chart shows a viscosity of 200 cSt at that temp, but about 80 cSt with 10W-40 (you have to draw your own lines for multi-weight oils)

So out went the SAE 40, and in went some Mobil 1 15W-50. At 100 deg F the viscosity is around 115 cSt. That oil seemed better when warm, but the acceleration was still too rich. (I judge that by plug condition, and the deeper "note" of the exhaust sound).

I ended up making a 50-50 blend of the 10W40 and 15W-50 - a 13W-45, if you will. This gives a viscosity of about 100 cSt at 100F, which is less than that of SAE 30 (130 cSt). This seems to work very well for now.

An oil with the viscosity of a 5W-60 looks like it would work very well, but I doubt it exists. I did not try SAE 30 because the viscosity is so much higher than both 15W-50 and 10W-40 below 100F. Again - what works for me may not for you.

Brent B

May I ask why you didn't try the DASHPOT oil that Moss and the others sell. Don't know what the viscosity is but I was just thinking that that oil was made for the carbs. Just wondering. Maybe someone knows something I don't. I run it in my 73 TR6 with dual Stromberg and it seems to work fine.

JW's question is a good one. There have been other threads about using engine oil in the carbs, but it has never been clear to me why, except for the comment "keep it simple" which I like a lot.

But why not use what they sell for the carbs?

JL Bryan

The very expensive "special dashpot oil" sold in the tiny bottle is 20 weight.

Rick O.
Rick Orthen

Another good question: What is the weight of "official" dash pot oil? Lets face does have a weight value. But are they willing to tell you this top secret info?
Maybe dash pot oil is sold as "official" dash pot oil for those who are not willing to experiment and gather experience and self taught knowledge.

Good info Brent. I invite you to come north where the goose now resides and experiment with our, shall I say, milder climate. We unfortunatly have a wide spread of temperature from Spring, Summer, and Fall.
Rick C
Rick Crawford

JW - A good question. I didn't use the "special oil" because I didn't have any, and I've heard like Rick that it's essentially SAE 20.

Rick - In your climate the Redline 10W-40 would probably be what I'd stick with as it has a narrower viscosity range than a straight weight. Provided I didn't drive at -20 dergees, that is...

Brent B

The callout to using "Zenith Lube Pack" SAE 20 oil in the dashpots is from an emissions testing document issued by BL's Rover Triumph division in 1973. I believe "3 In One" oil is close to this weight and was specified to reduce CO emissions compared to the relatively rich acceleration mixture produced by heavier weight oil.

Rick O.
Rick Orthen

I don't know if this is "very expensive", but I use Penrite Damper Oil, for SU/Strombergs. costs about $6 for 125ml. Don't know if available in USA.
Works fine.

Eric de Lange

My car developed a high speed missfire between 4500 and 5000 rpm.

I changed plugs, wires and finally checked the dashpot oil and found the levels to be too low.

So I grabbed my oil can from the work bench - can't remember what kind of oil is in that can - and topped up the carbs.

No she runs beauty and burries the tach through 6000 rpm with no hesitation.

I guess this old british stuff isn't too scientific.

My problem was just a lean condition as the carb openings got too big too fast with low dashpot oil levels.

The thicker the oil, the more rich condition is created.

73 5 speed.
John Parfitt

How can the "special dashpot oil" sold in the tiny bottle be expensive? I've only had to fill my carbs once so far and the bottle still has plenty left. Are people changing their dashpot oil as part of a maintence program? The only other reason I could see it being expensive is if the carbs were leaking and you had to continully put oil in. I just felt that with the amount of problems people say they have with Stromberg carbs that I would use what was recommended instead of trial and error. With my luck something would go wrong. Oh well, just thought I would put in my 2 cents worth. Hope this doesn't start a posting war. lol

Here's some interesting info about dashpots by Dan Masters that might help this discussion.
Charlie Ballard

You are absolutely correct. From the stand point of not changing it every year and the bottle lasting for years. I asked the question of what is the weight of "official" dash pot oil and my question got answered before I asked it (thanks Rick O:). Simply if you can buy the exact same weight oil for a lot less, then why buy the more expensive "official" stuff.
If you do not really think it is expensive then do the math from Erics' post. MAN!!!! that is expensive!!!! Maybe you paid around the same price.
Our LBCs are like boats. You put the name "boat" infront of a product and wammy! triple the price!
JW, what you are doing is not wrong. The points made here are simply that you can get the same stuff that does exactly the same thing for a LOT less.
Brent, thanks. I am currently using 10W30 ( Castrol) in my little squirt can. I think I can afford a dash pot oil change to 10W40 at a cost of $0.04:)
Rick C
Rick Crawford

This thread was discussed between 03/05/2004 and 05/05/2004

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