GT-40 Oil

[ajskier]

Good Afternoon All, I am looking for some advice after I have read about as much as I can regarding oil for my baby. I purchased the boat about 3 years ago and I have been using the same oil that the previous owner did in the boat, which he was using the same oil that the original owner was using who was a promo driver. With that being said the previous two owners were using Mobile 1 Full Synthetic High Mileage 10w-40. I have not had any issues with the boat using that oil, but after reading as much as I could about the proper oil for these motors and contacting PCM directly. I have a few questions that I am hoping that you all could answer for me. I was not really confident in the answers, that I got from the person I spoke with at PCM, she really didn't seem like she knew much about these motors and I am thinking what she was telling me was information for the newer motors, 1) What are you thoughts on the current oil? 2) From the research that I have been able to do, it seems that people are using a few different kinds of oil, but the key thing is to make sure that it has a high ZDDP rating. I looked up the current oil that I am using and it has a ZDDP rating of 900 PPM. Is this to low and what should be the minimum level that I should be looking for? 3) I know that this one is a loaded question, but what best oil I should be running in the motor? I have seen Racing oil or Diesel oil recommend by some. I have a friend that I ski with that is using Delo 400 SDE 15w 40 in his boat and he swears by, not sure why, but that is what he runs. 4) Is straight weight recommended, which the racing oil comes in or does that aspect not really matter? 5) I have talked to some mencanhics that say to always run the same oil in a motor and to not change from what has always been used. Is there any truth to that or is that a old wives tale? 6) If I do change oil, is there anything that I should do to flush the old oil out? If there is anything that I should be asking, but didn't, please tell me. I really appreciate all of your help and knowledge. Thank you, AJ

[a0128]

1) You don't need to run a synthetic oil in these motors (save yourself some money). 10w-40 is OK, but not the correct weight as specified by Correct Craft (PCM). Unless you are in an arctic climate the 10w part of the blend is slightly thin (meant to flow better in below freezing temps) and you may experience some increased engine noise upon startup as these engines were not manufactured with overly tight tolerances.

2) The ZDDP in the Mobil 1 10W-40 that you are running is too low. The GT-40 has flat tappets which require an oil with higher ZDDP levels. You should be running an oil with a minimum ZDDP level of 1200. 1400 is ideal.

3) Most GT-40 owners run Valvoline VR1 or Shell Rotella T4. Some run Royal Purple.

4) Original documentation specs 40 weight (for most temperate climates). Nothing wrong with running 40 weight, however it can be scarce in certain areas of the country.

5) Old wive's tale IMO.

6) No.


I run Valvoline VR1 racing Oil in 20w-50 along with a Mobil 1 oil filter. VR1 has the correct ZDDP levels. Avoid the orange Fram filters as they are poorly made. Autolite FL-1A or Wix are other brands folks use.

It is easy to over think this oil thing, Most important is to change your oil every 50 hours and at the end of the season. What you use is mostly up to you keeping in mind ZDDP levels and a weight that closely aligns with the OEM spec.

[CHassmann]

Valvoline makes the VR1 Racing oil in straight 40. I used it for the first time winterizing last year and again this year.

[rcsmith727]

I ran VR1 20w-50 this year and it worked great. Advance usually carriers this so it was easy to find. The 50w raised my oil pressure a little, but I hear that's not a problem - just means the seals are good I guess? I might order VR1 straight 40w for next year - thanks for the tip Chassmann

[CHassmann]

Just as an FYI, I ordered the VR1 from the local NAPA. It was in the next day and got a discount with my AAA membership.

[GMLIII]

I ran straight 40 W oil in my GT 40 for 15 years and no problem. Cheap oil and can be purchased at any auto parts store.

[Fgroce]

Okay we have a boat that we take to the lake, Lake time with family and friends is very precious. We don't get to go as much as we all would like, some people have very short seasons. Rebuilding a GT-40 can run 2-4 thousand depending. If you repower it can be 8000 plus. People always ask what oil to run? I always say run the best you can. I run Amsoil Diesel Marine oil 15-40. It has everything needed for a flat tappet cam shaft and is a mil spec rust preventative for storage. When some one says run a cheap low grade oil, it just does not make sense. Check out Amsoil Diesel Marine oil, if it works for you great. I have been running it for over 20 years. You will not be disappointed. If you have a boat with roller tappets, requiring modern oil they also make marine oils for that application too.

[CHassmann]

Great advice!

[GMLIII]

In the owners manual of my GT-40 engine it states to run straight 40 weight oil even though you probably could run 15w-40 as you suggest. Just the fact it is straight 40 weight makes the oil dirt cheap to purchase; nothing wrong with it . There again running it in my GT-40 for 15 years with no problems should make it clear it is ok to use it. Why run high price designer oil as you suggest in these engines makes no sense.

[a0128]

When some one says run a cheap low grade oil, it just does not make sense.

I don't think anyone here is advocating using a cheap low grade oil and none that have been recommended would be considered as such.

I've never heard of anyone having to rebuild their motor due to running an inferior oil. Most engine rebuilds are a result of neglect (i.e. inadequate or no servicing) or poor winterization (or lack thereof).

[DW SD]

I use straight grade 40W as specd
I bought royal purple but I’m not a loyalist.
Redline is a good brand.
Brad Penn is another.
Joe Gibbs is another.
Mobil 1 motorcycle if they sell the straight grade.
Delo is solid too.
High zinc seems to be consensus for flat tappet cams. (Non roller)

Not sure why to go off menu from pcm engineers and do multi-grade.

Multi grades were readily available when these engines were new.

I don’t necessarily have a bias against cheap or designer but do want to avoid being penny wise and pound foolish.





Sent from my iPhone using PLT Nautique

[ajskier]

Hello All, I am sorry for the extremely delayed response. This site has been blocked by company for some reason and I was able to finally get on today. I just wanted to provide an update, I ended up going with VR1 straight 40 as I was able to find it locally and in stock. I changed the oil as I was winterizing the boat, so I have had a chance to run it to see if I see any differences between what was being used and the new oil. I am hoping this winter stuff stops soon and I can get the boat out and start enjoying it. I really appreciate everyones feedback.

[Otto Throttle]

I have the HO 285 HP Carb in my 1999 Nautique. Oil filter is Fram Ph8a. I want the Mobil 1 - 310 extended performance. I think it is a little bigger can anyone tell me if that will work properly? Thanks!

[DW SD]

pretty sure PCM calls for 40 weight in that, too. There's a list of solid products above. I just bought a 12 pack case of Brad Penn 40 weight straight grade from Amazon for decent $. But just one guy's opinion and don't want to start oil wars.

[Otto Throttle]

After 1 year of the VR1 straight 40W oil and it performed flawlessly. It is what the spec calls for and since I am not out on any colder than 70 days I don't think it matters!!! Mobile 1 Filter too kicked butt! Filter cheapest at Wally World too!
Otto