Oil for '84 Caddy w/HT-4100

[StillLearning]

I recently inherited an '84 Cadillac Biarritz convertible and was wondering what oil you would recommend for the HT-4100 engine, which I am told has "flat tappet" lifters and requires an oil with a decent dose of zddp. I was told that the car was run on 10w-30 conventional with an STP zddp additive to protect the cam because there is not enough in the "modern" oil formulations. Apparently this motor is notorious for being problematic, so I am keeping my fingers crossed with it.

I am not wild about running an additive like that if I don't have to and was hoping there might be some good options that won't require the additive. I was thinking a diesel engine oil might be more inline, something like a Rotella T4 10w30. I also have 5qts of Formula Shell 5w30 I picked up on clearance if there is any chance that might be a reasonable option.

The car has about 55k miles on it and will likely be driven about 1 or 2k miles a year. It is a cruiser, not a race car (with only 135 laughable hp), though it does have to rev that under powered engine sometimes to pull hills in my area without holding up traffic.

I am not committed to conventional either, if a synthetic or blend might be a better option, that is what I will likely go with. We intend to keep the car in the family for quite some time, as my FIL wanted my daughter to have the car, and she is still at least 10yrs from driving age.

Any input appreciated. Thanks!!

 

[dave1251]

If there has to be over 1500PPM of ZDDP to protect a daily driver it's not worth keeping. So skip the STP The Rotella will work well.

 

[StillLearning]

I am honestly not sure how much ZDDP is required to protect sufficiently. How much ZDDP does the Rotella have, or is there more at play than just the levels of that particular additive?

Just for reference, does anyone know about how much ZDDP used to be present in mainstream automotive oils available when this engine was put into production?

 

[ka9mnx]

At 135hp it's a very mild EPA engine. Meaning no high lift/high spring pressure camshaft. Anything over 700ppm (actually 600) ZN is all that is needed. Being a Caddy it's not a high revving engine (5,500+). Any modern oil will work but "I" would choose a HM oil and one with an ACEA A3/B3 or A3/B4 cert.

 

[StevieC]

I think much higher ZDDP levels were called for because the general additive package in oils of yester-year weren't up to the task as they are now.

 

[ka9mnx]

Originally Posted by StevieC
I think much higher ZDDP levels were called for because the general additive package in oils of yester-year weren't up to the task as they are now.


True. And the ZN today isn't the ZN of 1984. Moly has also replaced the need for high ZN.

 

[passgas55]

Conventional 10/30 Chevron Supreme
Semi 10/30 Delo
Full 10/30 M1 HM

Those would be my choices

 

[dave1251]

Originally Posted by StillLearning
I am honestly not sure how much ZDDP is required to protect sufficiently. How much ZDDP does the Rotella have, or is there more at play than just the levels of that particular additive?

Just for reference, does anyone know about how much ZDDP used to be present in mainstream automotive oils available when this engine was put into production?


Studies have shown around 800PPM to be better than sufficient. Around 1300PPM it starts to cause damage. Rotella will have 1000-1100PPM.

 

[kschachn]

Originally Posted by ka9mnx
True. And the ZN today isn't the ZN of 1984. Moly has also replaced the need for high ZN.

I don't understand, you're saying they used some zinc compound other than ZDDP in 1984?

 

[FlyNavyP3]

I see no reason not to just run Rotella T4 10w30 year round. I've had the (dis)pleasure of rebuilding a couple of these 4.1L disasters in a shop I used to work in. One came back at about 14,000 miles with a flat camshaft. Owner had been taking it to quick lubes for service. New cam lifters bearings and rings got it back on the road. Advised the shop installing the engine and owner of the vehicle to use Rotella T4 10w30 to avoid further problems, never saw the engine again so I assume no news was good news.

For non race applications with flat tappet camshafts we always recommended Rotella T4 10w30 as the average customer wasn't going to seek out a Joe Gibbs or Brad Penn oil from us or another race shop for routine oil changes but they can get Rotella anywhere.

 

[Garak]

Another option to consider would be Valvoline VR1 in 10w-30.

 

[BrocLuno]

VR-1 would certainly do the job just fine. It has been keeping flat tappet engines happy for more years than most of us have been alive. But any decent HDEO will have at least 800 PPM ZDDP, and many will have more. So something like an oil from Tractor Supply stores, or Farm & Fleet stores will do just fine too. And it may be a whole lot cheaper

 

[StillLearning]

Thanks for the replies and suggestions. I will most likely go with the Rotella T4 in a 10w30 for ease of acquisition, which also seems to work out well for cost.

The Valvoline VR1 also sounded like an interesting option, but I can't find it locally in that grade. If I wanted a 20w50 it would be no problem, but shipping and markup on that grade over the other grades of VR1 tend to make it cost prohibitive. Even Walmart wants over $20/qt!

Just out of curiosity, can anyone tell me how the moly in today's oils compares to the zinc in the oils of the past? It seems from what I have understood that moly has sort of "replaced" zddp in oils because it is less harmful to emissions equipment. That said, would a high moly, low zddp oil of the correct grade protect protect parts in boundry as well as the same grade with low moly and high zddp content?

 

[dave1251]

Originally Posted by StillLearning
Thanks for the replies and suggestions. I will most likely go with the Rotella T4 in a 10w30 for ease of acquisition, which also seems to work out well for cost.

The Valvoline VR1 also sounded like an interesting option, but I can't find it locally in that grade. If I wanted a 20w50 it would be no problem, but shipping and markup on that grade over the other grades of VR1 tend to make it cost prohibitive. Even Walmart wants over $20/qt!

Just out of curiosity, can anyone tell me how the moly in today's oils compares to the zinc in the oils of the past? It seems from what I have understood that moly has sort of "replaced" zddp in oils because it is less harmful to emissions equipment. That said, would a high moly, low zddp oil of the correct grade protect protect parts in boundry as well as the same grade with low moly and high zddp content?



Boron and moly are a couple of fricton modifiers or antiwear additives. Neither replace ZDDP fully.

 

[Linctex]

You need to really watch the condition of your coolant with these engines. I'm really surprised yours is still alive - it has to be one of the last running examples.

 

[Garak]

Originally Posted by StillLearning
The Valvoline VR1 also sounded like an interesting option, but I can't find it locally in that grade. If I wanted a 20w50 it would be no problem, but shipping and markup on that grade over the other grades of VR1 tend to make it cost prohibitive. Even Walmart wants over $20/qt!

Good grief. Our Walmarts only have it in 20w-50 (so useful in Saskatchewan), but it's very cheap, relatively speaking. As for how much moly, you'll want a lot of moly to venture into the anti-wear regime.

 

[Gasbuggy]

The cam in that engine is barely moving the lifters. I wouldn't bother running anything special in it.

 

[DGXR]

Originally Posted by Linctex
You need to really watch the condition of your coolant with these engines. I'm really surprised yours is still alive - it has to be one of the last running examples.



Makes me want to suggest the OP get rid of this car... unless it has sentimental value, the will/trust prevents unnloading it, or if the family would disown you for doing so. Definitely off-topic, I'm just saying an inherited item does not have to be cherished as the previous owner may have done.

 

[vssjim]

i would what ever 10-30 you want with a zink additive, don't know what brands you have the the Lucas stuff here is all around. Don't forget to always add the Coolant Tabs, Bars Leak and AC Delco sell them still