Synthetic oil 5w/40 or 15w/40

[1999gmc]

Just wondering if people are running 5w/40 in their trucks. And if so was the oil pressure any lower with it vs. 15w/40. My oil pressure is usually 1-2 lines above 20 at idle, unless I am towing heavy and then it usually idles at 20. Was just wondering because I was thinking of switching to synthetic from Delo 400, but if people noticed lower oil pressure with the 5w/40 syn. I would go to 15w/40 synthetic.

 

[JMJNet]

When the oil heat up, it should be the same pressure.

the first no 5 vs 15 is the viscosity level (it is a rating value) at cold temp.
With lower no. means a thinner when it is cold.
So, in the real cold country like subzero F, that becomes a factor in starting the engine.

IMO, for California which has relatively mild climate, just take your pick.
I don't think it will make too much difference except some people said that synthetic reduces wear.

The cost advantage happen when you do extended oil change interval (OCI).
Which the synthetic can potentially last longer without losing its ability to lubricate the engine.

Most Synthetic is 5W-40 while I only found 1 15W-40 Synthetic from Amsoil.

 

[tanman_2006]

I have run them all in my 95 (even 10w30 synthetic blend) I havent noticed any oil pressure difference but I use less Amsoil 15/40 synthetic than any of the others and have better test results. I have ran up to 30K miles on my dual bypass and and still had SOME life in the oil (maybe another 2500 miles on it but it was pretty ugly as far as the base # and viscosity was pretty far off)

I have had my best luck with amsoil 15/40 in the 6.5 but my Dmax really likes the 5/40 synthetics so I just use quality filters and mobile 1 5/40.

 

[matuva]

Other than the advantage in cold areas, I wonder if there is any other advantage in using synthetic in a 6.5 engine.

Personnally, I don't think it is worth it. I believe good respect of oil change intervals and a good conventional 15W40 (Delvac, Rotella, etc...) is more than enough... and it is cheaper without sacrifying health & longevity of your engine.

 

[tanman_2006]

Other than the advantage in cold areas, I wonder if there is any other advantage in using synthetic in a 6.5 engine.

Personnally, I don't think it is worth it. I believe good respect of oil change intervals and a good conventional 15W40 (Delvac, Rotella, etc...) is more than enough... and it is cheaper without sacrifying health & longevity of your engine.

We'll find out soon. I will be pulling and rebuilding my 95's engine soon and it has over 100K miles of synthetic and extended oil change intervals. Just about always tested before changing and usually got atleast 15K before the oil was past the point I wanted to use it. I dont tow heavy with that truck and do alot of highway driving so I saw the returns on the method but that doesnt mean its the best way for everyone.

 

[WarWagon]

Blowby would be a good indicator of how well it did.

The synthetic oil usually gave me higher oil pressure on gas engines.

The synthetic oil holds up better to extreme conditions including high extended heat.

The only way you know you should have had synthetic oil is if you scuff a piston or suffer engine damage after exceeding the limits of conventional oil. Corvettes use synthetic oil because GM didn't want to pay for oil coolers, that we have, and the oil temps exceeded 300 degrees with high load driving.

This said I have only scuffed 1 piston attributed to shock cooling more than anything and another oil failure due to fuel dilution. Pretty hard to overcome the limits of conventional oil. Then I remind myself I was running a 2 quart oil cooler on my 2008 Duramax and it needed it! (But still got near 10K oil changes.)

I would run the thicker base stock oil (15) because it doesn't use as many viscosity enhancers.

Not much difference between conventional and snake oil marketing of the synthetic name now. Synthetic (but not all brands) starting from a conventional base oil and all.

With a dirty 6.5 there will be enough soot dumped in the oil to eliminate any extended drain intervals you would get from a synthetic oil. After all towing the book calls for 2500 mile oil changes! UOI confirmed I was pushing my luck at 3-3500 miles in 1 week on a 6.5!

 

[tanman_2006]

Blowby would be a good indicator of how well it did.

Barely any blow by, I tried to film it but my camera wouldnt pick any up. I have 200K on the engine. To film it I drove for ~1.5hrs and ~80 miles then pulled the cdr out and didnt get enough to worry about.

 

[Jorge6.5]

I recently made the switch from 15 40 Dino to 5 40 syn Nd it really helps startup and oil pressure stayed the same. I like it a lot. Running Rotella t6 synthetic 5w40. It's worth it and I think im sticking to it year round

 

[jrsavoie]

I've always used Amsoil 5W30 year round

 

[jmiller]

I've been on the Rotella T6 for almost two years. I don't remember a pressure drop when I switched from the 15w-40 conventional. If any it was minimal.

Definitely better cold starts, and not having to switch viscosities between 5x-30 and 15w-40 is nice too.

The impact of the three oil cooler incidents was also reduced with the synthetic. Especially the last one, the 5 psi drop might have become a wiped bearing or worse on conventional oil.

 

[NVW]

AFAIK -5F is the lowest for me, if I can I plug in after freezing temps. Electricity is cheaper than a spun bearing. I use 0w-40 in winter.

 

[1999gmc]

Blowby would be a good indicator of how well it did.

The synthetic oil usually gave me higher oil pressure on gas engines.

The synthetic oil holds up better to extreme conditions including high extended heat.

The only way you know you should have had synthetic oil is if you scuff a piston or suffer engine damage after exceeding the limits of conventional oil. Corvettes use synthetic oil because GM didn't want to pay for oil coolers, that we have, and the oil temps exceeded 300 degrees with high load driving.

This said I have only scuffed 1 piston attributed to shock cooling more than anything and another oil failure due to fuel dilution. Pretty hard to overcome the limits of conventional oil. Then I remind myself I was running a 2 quart oil cooler on my 2008 Duramax and it needed it! (But still got near 10K oil changes.)

I would run the thicker base stock oil (15) because it doesn't use as many viscosity enhancers.

Not much difference between conventional and snake oil marketing of the synthetic name now. Synthetic (but not all brands) starting from a conventional base oil and all.

With a dirty 6.5 there will be enough soot dumped in the oil to eliminate any extended drain intervals you would get from a synthetic oil. After all towing the book calls for 2500 mile oil changes! UOI confirmed I was pushing my luck at 3-3500 miles in 1 week on a 6.5!

This was kind of why I was thinking of using synthetic. I live in northern CA and tow our toyhauler up highway 80 a lot going camping in the summer. A lot of times it is near 100 outside towing up 6-7% grades. And was just thinking the synthetic might be a better choice for the summer heat. I always try to get out of work and on the road before noon, which puts me in the mountains by 1:00 or so, but a lot of times it just doesn't happen and I am towing at the hottest part of the day.

 

[turbovanman]

Old thread but synthetic Rotella 5w40 all the way. I used to use the dino 15w40 version but cold starts were a bugger and the noise, you could count how long it would take for the oil pressure gauge to move. Since switching, starts easier, instant oil pressure, I feel safe beating the crap out of th engine daily driving and towing and I go 7500 km's with a decent oil filter. I had the pan off at 180K and bearings looked good.

 

[Will L.]

After testing thousands of engines under every circumstance engineers could come up with, the clear winner is... Either one. Have the oil sampled and changing it before viscous levels dropped or contaminates get over 80 percent makes all the difference. If you switch from conventional to synthetic expect oil leaks sooner. If synthetic from beginning no problems at all. Google the difference in moleculer chain shapes and structure to see why that happens, no fix oil wise just throw in the gasket and keep going.

In my hummer that I care about- delo400. In the 6.0 suburban with over extended oil changes (10,000 miles 35% city)-cheapest junk in a bottle EXCEPT penzoil. I am under legal order to not say why, but I don't run it.

 

[turbovanman]

cheapest junk in a bottle EXCEPT penzoil. I am under legal order to not say why, but I don't run it.

Hmmmmmm, interesting. Isn't it liquid balls in a bottle or something like that? :rof:

 

[WarWagon]

Old thread but synthetic Rotella 5w40 all the way. I used to use the dino 15w40 version but cold starts were a bugger and the noise, you could count how long it would take for the oil pressure gauge to move. Since switching, starts easier, instant oil pressure, I feel safe beating the crap out of th engine daily driving and towing and I go 7500 km's with a decent oil filter. I had the pan off at 180K and bearings looked good.

Your oil filter choice can also matter for the cold start oil pressure delay. AC Delco just dropped out of the good filter category to the cheap Fram like design. This means the anti drain back valve in the filters like Fram may as well not be installed because they don't work. Your engine clatters longer filling the oil filter back up. Silicone valves like Wix and Mobile 1 are the way to go.

Synthetic oil use is almost guaranteed to leak out of the 1990's oil cooler lines at the crimps. Gas or diesel engines. Even NEW GM hoses would leak synthetic. GM has since changed the design a little, but, I found synthetic still gets them.

I have had better oil pressure recently with a 15w-50 synthetic blend. A straight weight oil in our warm climate on long hauls without viscosity improver to break down is a good idea. (As someone reminded me of. :thumbsup: )

IMO the engineers mentioned weren't playing with a LS2 in a Trailblazer SS or Corvette lacking a oil cooler. There is a clear winner when temps get high (like 300 degrees oil temp) and that is synthetic. Yes the application needed an oil cooler and yes the GM bean counters were too cheap to install one. Yes, the hot running LS2 spits out rod bearings at an early age... Sludge failures plugging the oil pickup screen from specific Toyota and Dodge engines is reduced with synthetic oil use. The sludge, best I could tell from reading about it, was from high temp areas in the engine.

Step up to emissions strangled Duramax engines and you are running the fine line of what a conventional oil can handle. I did run that fine line and did go over it. The low oil pressure stop engine comes on at 9 PSI and I did see that warning on a 115+ degree day after towing. I am not sure how it would have done without the extra huge engine oil cooler. There was room to tow a bigger trailer. From a cost standpoint conventional did the job for 115K. Cost for my bottom line was the ONLY reason I didn't run synthetic. Only a few samples came back 'bad' like low viscosity with the warning message oil. We were running near 10K miles per the oil life monitor and can say it is fairly accurate. Change the oil when you suspect an issue.

In summery conventional oil can handle 90% of what is out there and use. When things get "extreme" like hot outside and you are towing hard or running hard in the mountains this is where synthetic could do you some good. Hot idle with the AC blasting stuck in traffic is also hard on engine oil.

MPG and other benefits left out of the discussion.

 

[Big T]

SoCal and I've been running Rotella T6 with no loss in oil presssure. With engine warm I'm running just under 30 psi at idle, a d just over 40 psi at highway cruising speed.

Walmart now has Delo Synthetic for $19.98 per gallon and I will try running that.

I'm running the oil 7,500 miles which is more than twice on conventional oil and it doesn't cost twice as much, so that's my cost savings.

I had leaks, but it was due to one of the stainless oil line fittings leaking at the block. A simple re tightening cured that. I would not run synthetic on any engine that consumes oil or has significant blowby. My '99 conusumes like 1/2 quart every 3,000 miles, now that I've stopped the leaks.

My '99 is approaching 200K miles on the engine and running well. Hope it goes 300K.

 

[tanman_2006]

SoCal and I've been running Rotella T6 with no loss in oil presssure. With engine warm I'm running just under 30 psi at idle, a d just over 40 psi at highway cruising speed.

Walmart now has Delo Synthetic for $19.98 per gallon and I will try running that.

I'm running the oil 7,500 miles which is more than twice on conventional oil and it doesn't cost twice as much, so that's my cost savings.

I had leaks, but it was due to one of the stainless oil line fittings leaking at the block. A simple re tightening cured that. I would not run synthetic on any engine that consumes oil or has significant blowby. My '99 conusumes like 1/2 quart every 3,000 miles, now that I've stopped the leaks.

My '99 is approaching 200K miles on the engine and running well. Hope it goes 300K.

I've been running amsoil 15/40 synthetic since 150k w/ dual remotes on 50 K intervals. 293k on my 95 and uses 1qt every 10-15k. I found my cost savings.

Source Unknown

 

[turbovanman]

Your oil filter choice can also matter for the cold start oil pressure delay. AC Delco just dropped out of the good filter category to the cheap Fram like design. This means the anti drain back valve in the filters like Fram may as well not be installed because they don't work. Your engine clatters longer filling the oil filter back up. Silicone valves like Wix and Mobile 1 are the way to go.

Synthetic oil use is almost guaranteed to leak out of the 1990's oil cooler lines at the crimps. Gas or diesel engines. Even NEW GM hoses would leak synthetic. GM has since changed the design a little, but, I found synthetic still gets them.

I have had better oil pressure recently with a 15w-50 synthetic blend. A straight weight oil in our warm climate on long hauls without viscosity improver to break down is a good idea. (As someone reminded me of. :thumbsup: )

IMO the engineers mentioned weren't playing with a LS2 in a Trailblazer SS or Corvette lacking a oil cooler. There is a clear winner when temps get high (like 300 degrees oil temp) and that is synthetic. Yes the application needed an oil cooler and yes the GM bean counters were too cheap to install one. Yes, the hot running LS2 spits out rod bearings at an early age... Sludge failures plugging the oil pickup screen from specific Toyota and Dodge engines is reduced with synthetic oil use. The sludge, best I could tell from reading about it, was from high temp areas in the engine.

Step up to emissions strangled Duramax engines and you are running the fine line of what a conventional oil can handle. I did run that fine line and did go over it. The low oil pressure stop engine comes on at 9 PSI and I did see that warning on a 115+ degree day after towing. I am not sure how it would have done without the extra huge engine oil cooler. There was room to tow a bigger trailer. From a cost standpoint conventional did the job for 115K. Cost for my bottom line was the ONLY reason I didn't run synthetic. Only a few samples came back 'bad' like low viscosity with the warning message oil. We were running near 10K miles per the oil life monitor and can say it is fairly accurate. Change the oil when you suspect an issue.

In summery conventional oil can handle 90% of what is out there and use. When things get "extreme" like hot outside and you are towing hard or running hard in the mountains this is where synthetic could do you some good. Hot idle with the AC blasting stuck in traffic is also hard on engine oil.

MPG and other benefits left out of the discussion.

I use Amsoil or K@N filters. Ever seen 15w40 dino oil at sub zero temps, its like molasses, compare it to synthetic 5w40, that's why it takes time for the oil pressure to move.

For the price of synthetic vs dino oil and the fact I go longer, add on better engine protection etc, its a winner for me. Others like dino oil and it works. Stick with what you like.

MPG isn't an issue, never ever ever ever seen it better/worse mpg running dino vs synthetic vs thinner oil vs thicker oil in any vehicle I"ve over owned in 27 years, your results may vary.

 

[Dieseldad97]

I've been diesel for many years, 5.7, 6.2, 6.5 and now Dmax. I've used all kinds of oil, and found full synthetic 0-40 the best for me. I use it year round and change oil every 15 thousand miles or so.