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Discussion Starter #1
Hi guys, I have a new to me 94 bronco xlt 5.0lt. Previous owner put viscus crx 25w60 at last oil change. He said he put it in because that is what he had laying around.
Is it safe to chance to a lowe viscosity? I was thinking 10w40
 

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Here in the temperate latitudes, we run 10w30 in cast iron ford engines. My all aluminum 4.6 dohc took 5w20.

For those who aren't fluent in oil ratings, a 10w30 is a 30 weight oil that acts as a 10 weight when cold (0°F usually). A 10 weight is thinner than a 30 weight. They do this so your 30w oil will still be fluid in cold temps. At 0°F, 30w would flow like molasses at the north pole. But 10w still flows like table syrup. This keeps the engine protected at all temps. You cant use straight 10 weight though because at 200° F, it would be the consistency of water, and not protect the engine properly.
 

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OP, that oil is too heavy for all season but will work for vehicles that see no use in below or at freezing conditions. I agree with MS88Bronc he may have used it to mask engine noise that may be a preexisting problem or to limit oil consumption. Put some non synthetic 10w30 after letting it drain for a while and listen for any changes, low pressure or leaks. Ford recommended 5w30 in their pushrod engines I believe.
 

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Here in the temperate latitudes, we run 10w30 in cast iron ford engines. My all aluminum 4.6 dohc took 5w20.

For those who aren't fluent in oil ratings, a 10w30 is a 30 weight oil that acts as a 10 weight when cold (0°F usually). A 10 weight is thinner than a 30 weight. They do this so your 30w oil will still be fluid in cold temps. At 0°F, 30w would flow like molasses at the north pole. But 10w still flows like table syrup. This keeps the engine protected at all temps. You cant use straight 10 weight though because at 200° F, it would be the consistency of water, and not protect the engine properly.
Here is some info that seems contrary to your explanation:

"Scientists discovered the use of polymers and the fact that these would expand with heat. VI Improvers are polymer material that expands as the oil warms up. This does NOT thicken the oil as is often stated. It merely slows down the rate at which oil thins out as the temperature rises. The base oil in use in a multi-grade (aka multi-seasonal) is the first number (such as 10W or 20W), where as the second grade is the viscosity achieved using the VI Improver (such as 40 or 50). 20W50 is a base oil of SAE 20W and the viscosity grade at running temperature is SAE 50."

I like to cover my butt and use Delo 400LE Full Synthetic 5W-40, covers low to high temps and I only need 1 oil throughout the year. Just my Personal Choice.
 

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How many miles does your '94 have on it? Did you do a compression check before purchasing it? That oil rating might actually be harmful to your bearings. Ford recommends using 5W30 in most climates which is what I use in my Bronco 351W engine.. I run 10W30 in the '69 Ford 302 in my Mustang but those engines were built to much looser tolerances than the newer versions like those in the gen 5 Broncos.
 

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Discussion Starter #7
Hi, thanks fof the quick replies. The truck has 130k miles. I decided to try 10w30 and everything seems fine for now. No noise or leaks yet. Ill let it sit and check on it in the morning.
Weather here never gets below 10 centigrade so i was planning on 15w40 but it wasn't available.

Thanks
 

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Here is some info that seems contrary to your explanation:

"Scientists discovered the use of polymers and the fact that these would expand with heat. VI Improvers are polymer material that expands as the oil warms up. This does NOT thicken the oil as is often stated. It merely slows down the rate at which oil thins out as the temperature rises. The base oil in use in a multi-grade (aka multi-seasonal) is the first number (such as 10W or 20W), where as the second grade is the viscosity achieved using the VI Improver (such as 40 or 50). 20W50 is a base oil of SAE 20W and the viscosity grade at running temperature is SAE 50."

I like to cover my butt and use Delo 400LE Full Synthetic 5W-40, covers low to high temps and I only need 1 oil throughout the year. Just my Personal Choice.
Seems we explained the same thing, but two completely different ways. Mine was from memory, and not very technical. Whatever the science is behind it, the first number is the weight cold, and the second is the weight at operating temp. At any given temperature, a 50w will flow slower than a 20w.

For somewhere that never sees freezing temps, ie the OP, yes a 15w40 would be great in these engines. I used to run the delo 400 15w40 in my 95 460. I live in one of the areas with the most fluctuating temperatures I've found. Winter temps often at 0°F and summer temps reaching 110° F. I've never had a problem with 10w30 year round.
 

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Hi, thanks fof the quick replies. The truck has 130k miles. I decided to try 10w30 and everything seems fine for now. No noise or leaks yet. Ill let it sit and check on it in the morning.
Weather here never gets below 10 centigrade so i was planning on 15w40 but it wasn't available.

Thanks
Your welcome and welcome to the forums. Are you in South America? If so good to see Broncos still running there.
 

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Yo Bromco,
WELCOME!
ASAP, find out if speed control, if equipped, recall work completed by a dealership. Call local dealer or register and view status @ https://owner.ford.com; or @ https://vinrcl.safercar.gov/vin/ ... have VIN ready.
"Summary: ON CERTAIN PICKUP TRUCKS, PASSENGER VEHICLES, SPORT UTILITY VEHICLES, AND MOTOR HOMES CHASSIS, THE SPEED CONTROL DEACTIVATION SWITCH MAY, UNDER CERTAIN CONDITIONS, LEAK INTERNALLY AND THEN OVERHEAT, SMOKE, OR BURN. THIS COULD RESULT IN AN UNDERHOOD FIRE."
To confirm current status, use this guide by jowens1126 @ https://www.fullsizebronco.com/forum/23-technical-write-ups/457065-93-94-96-cruise-control-recalls-repair.html#post6530073
note that the 93 recall is different than 94-96

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1994 Bronco Brochure, Partial; Cover & Page 3; plus pics of EDDIE BAUER model accessories.
by BigRob at 1994 Ford Bronco Bronco Accessories pictures, videos, and sounds | SuperMotors.net

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Yes, you can run different weight oil. Typically 5 or 10 /30 is great. 15/40 is also great when warmer.
The motor won't care.
 

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Agree with what's already been said. If it's really cold then even a 0-30w isn't a bad option
 
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