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Can you mix 10w-30 and 10w40 motor oil?

DiggetyDan

Jr. Member
Joined
May 3, 2005
Messages
97
Loc.
Beverly
I just came up from the garage - figured i'd do a quick oil change before heading out for a drive. I thought I had a box full of oil but forgot i had given the wife an oil change a couple weeks back. It turns out I have 2 quarts of 10W-30 and 2 quarts of 10W-40.

Would it damage the engine if I combined these two?
 

scottmcwms

Sr. Member
Joined
Jul 19, 2005
Messages
858
Loc.
Montgomery, TX
It won't damage the engine if you change the oil again quickly. Never, Never, Never combine oils. Don't even use the same viscosity oil from different manufacturers. There are unique additives for each oil and sometimes they don't play well together when mixed. You will probably be OK, but why risk having to pay $1000 or so to overhaul an engine. Don't do it. Better safe than sorry.

Scott
 

Jeepster

Bronco Guru
Joined
Jul 13, 2001
Messages
1,507
scottmcwms said:
It won't damage the engine if you change the oil again quickly. Never, Never, Never combine oils. Don't even use the same viscosity oil from different manufacturers. There are unique additives for each oil and sometimes they don't play well together when mixed. You will probably be OK, but why risk having to pay $1000 or so to overhaul an engine. Don't do it. Better safe than sorry.

Scott

Are you serious? :eek:

If thats the case I've been flirting with disaster for years when i do my monthly *"Polish oil change"







*add a qt when low
 

Hogback

Sr. Member
Joined
Sep 19, 2004
Messages
524
same here. Been doing that to my wifes car since it was new. It's never seen a wrench and it still purrs like a kitten at 200K miles.
now too bad the wife doesn't....;)
 

rellimgneb

Sr. Member
Joined
Feb 1, 2006
Messages
476
Loc.
Reno, Nv
Honestly it's just oil. It just coats metal parts so they can slide on other metal parts without getting too hot. Mixem, matchem, do whatever you want as long as they are lubricated.
 

astark

Contributor
Bronco God
Joined
Jun 16, 2001
Messages
7,349
Nice motor pic in your gallery :cool:

But I don't think four quarts is enough to change your oil anyway. So go get a case of Castrol 10-40 and a couple of Motor Craft filters ;)
 

TJK74

Bronco Guru
Joined
Feb 21, 2003
Messages
3,154
Loc.
Newark CA
DiggetyDan said:
I just came up from the garage - figured i'd do a quick oil change before heading out for a drive. I thought I had a box full of oil but forgot i had given the wife an oil change a couple weeks back. It turns out I have 2 quarts of 10W-30 and 2 quarts of 10W-40.

Would it damage the engine if I combined these two?

You will be fine with that. They will mix right in with each other and no harm will be done. Even if you were to mix syn with conventional you'll be fine. If you were to labratory test your oil it will read out as not a true 10w-30 but no harm will be done. Your good.
If your doing this in a pinch cause you need to add oil then go for it but if you can like stated above get yourself 6 or so quarts of what you need when you do it the first time;D
 
Last edited:

ken75ranger

Bronco Guru
Joined
Jan 27, 2002
Messages
5,069
Loc.
Troy, NY
astark said:
I don't think four quarts is enough to change your oil anyway. So go get a case of Castrol 10-40 and a couple of Motor Craft filters ;)
That's just what I was thinking!
 

thegreatjustino

Contributor
Red Head Grease Monkey
Joined
Jan 23, 2002
Messages
15,624
Loc.
Stockton, CA
I've mixed oils before but always try to use the same viscosity for all six quarts. If you've ever seen two or more types of oil poured into a clear container, they will separate out. When they are running through the engine, I doubt that it's that big of a deal, but I wouldn't mix them intentionally on any kind of regular basis.
 

commonlaw

Sr. Member
Joined
Dec 17, 2004
Messages
435
Loc.
Seattle
Never had a problem mixing.

Also, I noticed that you are only putting 4 quarts in? Not sure of your set-up but that seems low.
 

astark

Contributor
Bronco God
Joined
Jun 16, 2001
Messages
7,349
I once mixed brand and viscosity, my shirt came out of the dryer wrinkled, I burnt some burgers on the barbeque, I ran out of toilet paper and then left my coupons at home when I went to the store.

Don't take a chance, you need to get more oil anyway and you might as well do it right, as that Bronco is your baby and it deserves the best you can provide.

If you take good care of your Bronco, it will take good care of you, and what you put into that relationship will be reciprocated.
 
OP
OP
DiggetyDan

DiggetyDan

Jr. Member
Joined
May 3, 2005
Messages
97
Loc.
Beverly
here's a mystery

My oil level is showing full after only 3 quarts, it's on the higher side of the safe line. I've got a 302 which from the sound of it should take 6? I drained the oil out of the bottom plug - I did notice there was another plug closer to the front of the vehicle on the same pan, does that need to be drained also?
 

Jeepster

Bronco Guru
Joined
Jul 13, 2001
Messages
1,507
DiggetyDan said:
My oil level is showing full after only 3 quarts, it's on the higher side of the safe line. I've got a 302 which from the sound of it should take 6? I drained the oil out of the bottom plug - I did notice there was another plug closer to the front of the vehicle on the same pan, does that need to be drained also?

yes, you are only draining 1 hump/ 1/2 the pan.
 

72Sport

Bronco Guru
Joined
Jul 8, 2002
Messages
2,954
Mustang pans have dual drain plugs. Broncos only have one. Someone has probably done an engine swap or changed pans for some reason.
 
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