Oil Change on a 403

boybach

boybach

Well-known member
Dec 9, 2020
1,033
195
63
Planning on doing an oil change on the coach in the next few days and wondering what grade of oil to use.

The 403 engine seems to be in good condition and doesn't really burn a lot of oil, mileage is 40,000 and the last 10,000 miles of that were done on
long cross-country trips.

I was thinking of using Castrol GTX 5/30 but my pals with higher mileage coaches and Olds Toronados both use Rotella 15w40. I know oil selection is a
very personal jar of worms subject, but as the coach is still in the fairly low mileage category, I could use some advice.

I've glanced at the rat blog BTW

TIA

Larry
--
Larry - Victoria BC -

1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
operational Onan genset, R134A A/C, New fuel lines
 
If you have peeked at the "rat blog" then you probably noticed that the Rotella 15w40 you are asking about is ranked #185 out of 242 oils listed. The
#1 oil is Quaker State 5w30 Full Synthetic and is selling at Walmart for under $20/5qt. If you are looking for something in a 40w there is also 0W40
Mobil 1 “FS” European Car Formula selling under $25/5qt. JWIT
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Unfortunately, Walmart Canada doesn't have that oil.

Larry
--
Larry - Victoria BC -

1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
operational Onan genset, R134A A/C, New fuel lines
 
> Unfortunately, Walmart Canada doesn't have that oil.
>
> Larry

Either one?
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Well I can see all the plusses using synthetics, but if I were to choose a conventional oil instead, what would be a good weight to choose? I intend
to change the oil fairly often. I use Castrol GTX 20-50 in my cars, what would be a reasonable weight to use in the 403?

Larry
--
Larry - Victoria BC -

1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
operational Onan genset, R134A A/C, New fuel lines
 
I have a high mileage 403. It uses a couple of quarts between 3500 mile
changes on 10w-30 Valvoline. So, I switched to 10w-50 Valvoline Dino oil.
Oil consumption dropped to 1 qt between changes. Better idle oil pressure
to boot. I am not a fan of Synthetics in these 40 year old engines. But,
your opinions WILL VARY.
Jim Hupy
Salem, Oregon

> Well I can see all the plusses using synthetics, but if I were to choose a
> conventional oil instead, what would be a good weight to choose? I intend
> to change the oil fairly often. I use Castrol GTX 20-50 in my cars, what
> would be a reasonable weight to use in the 403?
>
> Larry
> --
> Larry - Victoria BC -
>
> 1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything
> working but forgot the word NOT. New wiper blades, New SS exhaust system,
> operational Onan genset, R134A A/C, New fuel lines
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
FWIW - I run conventional Rotella 15W40 in my 455. I also run it in my oil-cooled BMW R1200R - but run synthetic in most of the other vehicles.

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> Planning on doing an oil change on the coach in the next few days and wondering what grade of oil to use.
>
> The 403 engine seems to be in good condition and doesn't really burn a lot of oil, mileage is 40,000 and the last 10,000 miles of that were done on
> long cross-country trips.
>
> I was thinking of using Castrol GTX 5/30 but my pals with higher mileage coaches and Olds Toronados both use Rotella 15w40. I know oil selection is a
> very personal jar of worms subject, but as the coach is still in the fairly low mileage category, I could use some advice.
>
> I've glanced at the rat blog BTW
>
> TIA
>
> Larry
> --
> Larry - Victoria BC -
>
> 1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
> operational Onan genset, R134A A/C, New fuel lines
 
I've decided to go with either dino GTX 5w30 or GTX 20/50, probably the 5w30 - thought about the rotella, but because of rat's shitty rating, decided
against it. YMMV

Larry
--
Larry - Victoria BC -

1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
operational Onan genset, R134A A/C, New fuel lines
 
Most definitely YMMV - I do run Castol GTX 10W30 in my Onan!

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> I've decided to go with either dino GTX 5w30 or GTX 20/50, probably the 5w30 - thought about the rotella, but because of rat's shitty rating, decided
> against it. YMMV
>
> Larry
> --
> Larry - Victoria BC -
>
> 1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
> operational Onan genset, R134A A/C, New fuel lines
 
> I've decided to go with either dino GTX 5w30 or GTX 20/50, probably the 5w30 - thought about the rotella, but because of rat's shitty rating,
> decided against it. YMMV
>
> Larry

You can always mix the two viscosities and end up with something closer to 10w40.

BTW, why not synthetic?
I always wait for sales and stock up, makes the price difference less of an issue, it's all expensive.

Oil is one of the things that can be debated upon forever and motorheads will never agree. For the most part, motor oil is pretty good nowadays,
some are just better than others at particular applications for whatever reason.
Plus, new products and data come up, gotta keep up to date on the latest snake-oil
--
Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model
 
I bit the bullet and bought the GTX 5w30. After reading through rat's analysis, there appeared to be no advantage to using synthetic as I'm not going
for long periods between changes.
I'll be doing an oil change either at 5000 miles or once a year- very doubtful I'll put 5000 miles on the charabanc in a season just hanging around
the island and lower mainland even of I go back up to the interior, 5000 miles would be pretty hard to clock in a season.
Plus engine wasn't really designed for synthetics and I don't fancy testing the extra leak theory either.
I was going to run the 20/50 but as most wear is at startup I thought going with the 5w would be better in the flow dept when cold.

Larry

--
Larry - Victoria BC -

1977 Palm Beach VIN TZE167V101295 - 40,000 miles, PO said everything working but forgot the word NOT. New wiper blades, New SS exhaust system,
operational Onan genset, R134A A/C, New fuel lines
 
In my case - I don't run synthetic oil in any of my older engines. But I do
run it in my newer engines... That's probably due to listening to old
wives' tales years ago.

So for the GMC - years ago I went looking for a conventional oil with high
ZDDP and have always been happy with the Rotella oils (conventional &
synthetic). I never looked back...

Rob
76 Royale Twin Beds, Dry Bath
Victoria, BC

> BTW, why not synthetic?
> I always wait for sales and stock up, makes the price difference less of
> an issue, it's all expensive.
>
>
> --
> Burl Vibert
> Kingston, Ontario
> 1976 GMC 26 foot, Sheridan reno, don't know original model
>
 
This is really annoying.....

I started to read Rat540's oil blog years back and then with several computer crashes the link was lost and I did not succeed in finding
https://540ratblog.wordpress.com/ until now. They guy is right, and I wish I could meet him. His results, both positive and negative, very much
agree with what I witnessed working in engine testing all these years.

Now that I have finally recovered the link, I have to restart digesting his 400+ page blog.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
Matt,

Based on the blog, Quaker State Full Synthetic 5W30 wins hands down. He states it the best for any water cooled engine.

Thanks for posting.

Everyone enjoy this holiday weekend and lets give thanks for the country we have inherited through the sacrifice of others. Lets also hope that we and
our young people are able to keep it.

Take care all,
Tom K.
--
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D.
 
> Matt,
>
> Based on the blog, Quaker State Full Synthetic 5W30 wins hands down. He states it the best for any water cooled engine.
>
> Thanks for posting.
>
> Everyone enjoy this holiday weekend and lets give thanks for the country we have inherited through the sacrifice of others. Lets also hope that we
> and our young people are able to keep it.
>
> Take care all,
> Tom K.

Matt,
This is the link that I use.

https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/

--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Dick Patterson's oil seminar is a pretty good presentation. Lots of material but the major takeaways I remember (they stuck!)
1) Do not use 50 weight oil. It opens the bypass more often, provides less flow therefore worse cooling to bearings.
2) use full synthetic.

Personally I have many old GM non roller cam vehicles and I don’t add ZDDP. I have never wiped a non roller cam
The only cam failure I have ever had was a ROLLER CAM.

I think 5000 miles is way too long an interval based on a 10 MPG fuel rate. Not so much that the oil is broken down at that point, but that’s a lot
of combustion byproducts to ask 5-6 quarts to suspend.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
> Matt,
> Based on the blog, Quaker State Full Synthetic 5W30 wins hands down. He states it the best for any water cooled engine.
> Thanks for posting.
> Everyone enjoy this holiday weekend and lets give thanks for the country we have inherited through the sacrifice of others. Lets also hope that we
> and our young people are able to keep it.
> Take care all,
> Tom K.

Tom,
This is why I have to digest more of the blog, in test lab work early in the low number oil years we saw a lot of "shear down". This is when the lube
oil molecules get broken up and so reduces the kinematic viscosity. A 5W oil will have a base stock that is only 3 to start with and we saw it go as
low as 1 during testing. The results of this were often notable.
As said, when I have finished, I may change my mind.

> Matt,
> This is the link that I use.
> https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/

Larry,
Thanks Larry, I was able to track it down again and have set a bookmark for it.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
You must log in or register to reply here.
Applied GMC
Get your shine on at www.cruzingear.co

Share this page

Share this page
Top Bottom
Back