: Oil for 4100

84 Eldo TC
04-09-11, 11:06 PM
Hi all, the 4100 engine in my 84 Eldo has that thumping noise which is still very minor. Which leads me to two questions,

1. I am running 10w40 conventional oil, can I run something a little thicker which would hopefully get rid of the noise, or would that cause the motor to fail faster?

2. Once these motors start making noise, are they in danger of self destructing soon, or are they still fine to drive?



04-10-11, 11:07 AM
I used 15/40 DELLO or ROTUNDA oil specified for diesel applications for years. The faint thump noise is generally the front crankshaft to bearing clearance. This noise has no effect on engine life.

84 Eldo TC
04-10-11, 04:48 PM
Thanks for the reply. Good to know that it's just a noise I can ignore, unless of course it gets really loud. I will try that weight oil to see if it gets quieter. Would 20w50 be too heavy? Also, do I need to use ZDDP additive in these engines? Thanks again.

04-10-11, 06:28 PM
Motor oil already has zddp in it, just in lower percentages than in the past. I would only use a zddp additive in an engine that has flat tappet lifters. My thunderbird has flat tappets and I use Comp Cams break-in additive in the oil. I could be wrong, but I believe the 4100 has hydraulic roller lifters like the rest of the 4.x series..

04-10-11, 09:28 PM
The 4.1 has flat tappet lifters and needs ZDDP

04-10-11, 09:42 PM
Wow I would not have thought that any engine made in the 80's would have flat tappets! What a dinosoar... This is what i use in my Thunderbird which is 15 years older and has hydraulic flat tappet lifters: http://www.summitracing.com/parts/CCA-159/

04-11-11, 09:02 AM
The Jeep 4.0 was still using flat tappet lifters until production ended in 2006.

04-11-11, 10:33 AM
4100's went to roller lifters in 1985. The Allante used roller lifters from the beginning.

04-11-11, 01:25 PM
Everything I've read says roller lifters didn't come until the 4.5. And although I haven't my engine that far apart, nothing in the FSM for my 85 4.1 looks like a roller lifter

04-11-11, 01:54 PM


Or this?

http://t3.gstatic.com/images?q=tbn:ANd9GcQKdeYOen5K2lsFYOvHmUBjaE30DccsT YTorsgBYUnSEgVn2DrsDw

04-11-11, 04:27 PM
Sorry shouldn't have said rockers. All of the 4.x use the same interference rockers (no rollers) like these (http://www.captfiero.com/cadero/imagepages/Valvetrain%20Caddy%204.9.html)

We're talking about the lifters (your bottom pic)

04-11-11, 04:56 PM
Which makes me wonder.... Are there any engines with factory roller rockers?

84 Eldo TC
04-11-11, 11:13 PM
Thanks for the feedback. I have ZDDP additive from Cam Shield and will add that to the oil.

04-12-11, 07:26 AM
I think any regular 15-40 truck oil has enough zdpp for the old flat tappet engines without having to buy an additive.

06-18-11, 07:45 PM
I Use Halvoline 10-40 and when I put this Prolong stuf in the oil 3 the noise from the lift var mutch more quiet on my Eldorado 1983

06-19-11, 03:02 AM