Hello,

I just recently came into owning a 1984 Cadillac Coupe De'ville with the HT 4100 engine. It now has around 51k miles on it. I was wondering from those of you who have owned the car for a while with that engine what are some good tips and pointers to help it last for many many more miles? Any help like on type oil to use, or other mods, etc would be great!

Thanks!

Gene

That is the second worst engine Cadillac ever made. You should plan on replacing it.

ehall is sort of correct about it being a not very good engine. Best you can do is change the oil regularly, and change the coolant each 2 years.

51,000 Miles? It's not even broke in yet! It's not a powerful engine, but it will do the job. This engine had some design flaws in the early editions, which were resolved in the later incarnations. Like anything mechanical, it thrives on proper maintenance. Use good oil, change it and the oil-filter religiously every 3k miles and flush the cooling system every two years. Add the required sealant tabs to the new coolant. Get an FSM for the car, if you don't already have one. Keep it in tune/pay attention to any trouble codes and it should get you there and back.

Also, use Diesel 15w40 oil (Shell Rotella / Delo 400) which is higher in ZDDP and will protect the non-roller cams and the distributor gear on this engine. The newer oils have drastically reduced ZDDP content to reduce cost and prolong catalaytic converter life. Higher ZDDP content is not also as crucial on newer engines with roller cams and other reduced friction points.

As mentioned,the 4.1 liter is definitely in the top 2 worst Caddy engines ever produced.Corrections were made in the later produced 4.5 and 4.9 liter.
Do what the other member`s suggested in preventative maintainance.You might get lucky (if the engine was well maintained before you got it) and it may last a while.
Good luck!

I don't want to enter some big argument here, but when it comes to using Diesel oil in a gas engine: I believe it to be bad idea. Diesels and gas engines have much different requirements. Last Dec when I installed a new GM rebuilt 4.1, I too was concerned about the lack of ZDDP in todays' oils. Instead of making myself more stressed, I used regular 30W Penz with a bottle of CompCam engine break-in oil. GM EOS is similar as are other brands. I will continue on that regimen.

my 4.1 has about 280K on it if the title is correct.
lacks pretty much everything my slantback had!

I have an email from Royal Purple Oli Co, and they told me that the diesel oil has more of the good additives than the "normal" oil sold today, but not as much as their oil, which is 1300 PPM (or PPB?) anyway, I have been using diesel as opposed to regular oil for two years in my 4.1, since it ate a cam. Royal Purple is expensive oil though, like $7.95 a qt at the local Advance auto parts store. Their racing oil is a bit over 14 bucks a qt. We are not left with very many options for flat-tappet engines.

The reason I started using diesel oil is because of an article in HOT ROD magazine a couple years back, about the oil problem. They said , at the time, that the diesel oil was a better deal than the regular stuff. But Royal Purple said the the ZDDP has been reduced in diesel oil also, to 1100PPM, as opposed to the old rating of 1300.

The GM design engineering guru who used to post on this board several years ago also recommended the use of diesel oil on these engines as well as the 93-99 Northstar engines. Too many people are experiencing worn out cams and it looks like the problem can be traced back to the lack of ZDDP in conventional gasoline oils.

LOL.....just reading to see if the amount of zddp was listed on the CompCam additive bottle. It isn't, but there is a last-sentence caveat: not for use in vehicles with catalytic converters. OH well! I guess you'd be more damned if you don't use it than if you do. My truck has a bullet-proof 4.9 and the DeVille has a new 4.1, both with CCs and both get the CompCam zddp additive....what, me worry?

I used Mobil 1 10W-30 Extended Performance in ours until an accident caused us to stop using the car. Those tabs recommended are probably the best advice I can give to help keep the water pump from failing. It was the one thing that failed a lot in our car until I found one with a lifetime warranty and realized from reading one of the labels in the engine bay that the tabs were necessary. We have approx. 120k miles and even though the oil leaks, it still ran well following the maintenance schedule in the manual diligently.

51,000 Miles? It's not even broke in yet! It's not a powerful engine, but it will do the job. This engine had some design flaws in the early editions, which were resolved in the later incarnations. Like anything mechanical, it thrives on proper maintenance. Use good oil, change it and the oil-filter religiously every 3k miles and flush the cooling system every two years. Add the required sealant tabs to the new coolant. Get an FSM for the car, if you don't already have one. Keep it in tune/pay attention to any trouble codes and it should get you there and back.

Thaks a lot for the information. My Grandmother bought the car in 84, and pretty much as she was retiring, so it was a grocery getter, and she kept up regular maitinence religiously. Looking under hood, the car has many new parts on it, including new water pump and I remember having all the oil leaks fixed by the dealer.
Could you give me a little more information about the "sealant tabs", I have no idea what they are. Also I do not know what an "FSM" is. I am not up on my lingo I know, lol. THANKS again!

LOL.....just reading to see if the amount of zddp was listed on the CompCam additive bottle. It isn't, but there is a last-sentence caveat: not for use in vehicles with catalytic converters. OH well! I guess you'd be more damned if you don't use it than if you do. My truck has a bullet-proof 4.9 and the DeVille has a new 4.1, both with CCs and both get the CompCam zddp additive....what, me worry?

The GM design engineering guru who used to post on this board several years ago also recommended the use of diesel oil on these engines as well as the 93-99 Northstar engines. Too many people are experiencing worn out cams and it looks like the problem can be traced back to the lack of ZDDP in conventional gasoline oils.

I am guessing what to take from this discussion is that I should either use Diesel oil or an additive to add to "zddp" correct? Would either of you kind Gents mind telling me what exactly that is? I have no idea here! Again thanks for the information, I am taking it all down!

--Gene

Dave, its funny you mentioned trouble codes, because the "Service Now" light just popped on in the car. The manual is not much help here as it just says drive to the dealer ASAP. So I guess I will have to do that eventually when I get back to the car...

--Gene

Thaks a lot for the information. My Grandmother bought the car in 84, and pretty much as she was retiring, so it was a grocery getter, and she kept up regular maitinence religiously. Looking under hood, the car has many new parts on it, including new water pump and I remember having all the oil leaks fixed by the dealer.
Could you give me a little more information about the "sealant tabs", I have no idea what they are. Also I do not know what an "FSM" is. I am not up on my lingo I know, lol. THANKS again!

I dug up an old receipt for the "SUPPLEMEN" Part Number: 3634621. Any Cadillac dealer parts department should have it. When you get it there are 6 huge brownish, (I am partially red/green color blind,) tabs and you mash them and just add the whole thing. After talking with the parts guy at my local dealer and seeing just how huge this is there is no surprise to me that the water pump would fail without adding it! While I never had any bad reaction to the stuff, (I used gloves,) please note the caution on the packaging about getting some kind of irritation or something like that.

I think FSM= Factory Service Manual, the one by Helm. I found it somewhat helpful, (it is huge,) but when the car wouldn't pass smog here in CA I couldn't solve the problem with it. But maybe that is just me because I'm not a mechanic.

Mods:
The tranny on our '85 seemed to love the Mobil1 ATF that I put in it. The huge 10.8mm ACCEL wireset and Bosch Platinum +4 plugs made it run better than when I started working on it. I couldn't find 10.8mm anymore but I'm assuming the thicker the wire the better, from experience. No other car in our household has run as smooth after changing the plugs and wires. I can't emphasize enough the importance of using good oil because one time my belt broke about 2 miles from home and I just drove the car all the way home and it didn't break down. (What I love about older cars is you can do the oil change without even lifting it up with jackstands!)

O ok, so this is something i insert into the radiator?

It's the same as this stuff

http://www.barsproducts.com/products/HDC.gif

Don't put too much in or it'll clog things up. All you need is enough for it to fill in any corrosion spots in the coolant channels.

Ok awesome, I will pick some of that up pronto...Thanks

It's the same as this stuff

http://www.barsproducts.com/products/HDC.gif

Don't put too much in or it'll clog things up. All you need is enough for it to fill in any corrosion spots in the coolant channels.

Hmm,

Sorry if I've been misinformed. When I originally saw the package I asked the parts guy, an older fellow who seemed very knowledgeable and honest, if I put one tablet in. His response was to put the whole thing in, but to mash it up into a powder before doing so. The GM packaging specifically says 1#3634621 so I'm assuming he was correct. (I still have two.) I used the whole thing and didn't seem to have any trouble...

The 4100 is the worst Cadillac engine ever IMO. IMO just change the oil at 3000 miles and the coolant at 10k, be sure to use the correct sealent tabs when you change the coolant. When your 4100 does blow up(that is a when, not an if), swap it for something better. I wouldn't hate on the 4100 so much if it had the same grunt as my old TBI 350 in my 1991 Brougham(which BTW is still pretty slow, but its adequate IMO)

The 4100 is the worst Cadillac engine ever IMO. IMO just change the oil at 3000 miles and the coolant at 10k, be sure to use the correct sealent tabs when you change the coolant. When your 4100 does blow up(that is a when, not an if), swap it for something better. I wouldn't hate on the 4100 so much if it had the same grunt as my old TBI 350 in my 1991 Brougham(which BTW is still pretty slow, but its adequate IMO)

I keep hearing this from people, and I'm not surprised people think so with all the water pumps we went through. But I must say following the recommended maintenance for severe usage, (although I'm not sure I remember the coolant change being so frequent,) as Aron has stated keeps the car running just fine. If my mom's accident which caused some difficulty in opening the passenger side door didn't happen, the car would still be in use today. In fact the car is still sitting in our driveway over the past year and a half because we were fond of it and the amount of work I put into it personally.