Oil temps-Aluminum-vs-Iron Blocks

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Dec 22, 2002
The Garden State
I have an aluminum 4.6L V-8 engine block in my 2002 Ford F-150. I think only the 2002 & 2003 F-150's had these blocks. What I read the 2004 have gone back to the cast iron blocks, as the previous 4.6L V-8 truck engines had, probably part of Ford's cost savings program. My question is does an aluminum block, assuming both engines having aluminum heads, bring the oil up to operating temps sooner, thus causing less engine wear due to "cold" oil. I know my water temp comes up rapidly, but I don't know about the oil temps. This info could be useful in estimating oil change intervals if you don't drive great distances during a time period. And yes I do UOA, but it isn't feasible to do them all the time.

Well Iron takes longer to warm up then aluminum. So I can safly assume that because of this. It would take iron longer to warm up and cool down opposed to aluminum.
They probably switched back to cast iron for two reason. 1)Cost!2) Durability! A truck block is a high torgue application not a high HP application. It is alot more expensive to build an aluminum block for high torque. You have to have more clearance on main bearings when the block and crank are made from materials with radicly different expansion rates. Even Toyota made their truck block out of cast iron even though it is based on the all aluminum lexus V8. Cast iron is stiffer pound for pound then aluminum and has some inherant lubricty property. Cast iron is more stable as well. You do not need to cast or press sleeves in the bores either with cast iron reduceing the chance of sleeve failure! While aluminum disapates heat better then cast iron I doubt that it would make a difference in oil temp. Once the aluminum engine becomes saturated with heat I doubt that it has enough surface area to make a difference.
I've owned two LT1 Firebirds and one LS1 Firebird, and the LT1 uses an iron block/aluminum heads, while the LS1 uses all aluminum for both. Both have similar (if not identical) sized cooling systems. Honestly, I noticed both engines taking the same amount of time for both the coolant and oil temps to come up (oil temp was estimated based on oil pressure) So I don't think it's the material used so much as the size of the cooling system which helps determine how quickly the engine's coolant and oil reach operating temperature. My wife's Honda is all aluminum and it warms up very quick, since it's cooling system is so tiny (less than 4 quarts!) If the cooling system warms up fast, so will the oil, since typically the oil temp tracks about 10-15 degrees under the coolant temp during initial warm up.
Thanks guys, Well so far that blows my idea of an aluminum block being better for raising oil temps on short trips versus a cast iron block with the same time to "heat" up the oil. I thought that the aluminum block would "heat" the oil up faster
. Thanks for your feedback

MNgopher owns one or two Ford 4.6L V8's and will probably chime in when he sees this thread. Look for his reply...if it's like his other posts it will offer some good insight.

I also own a 2003 4.6L V8...problem is, I don't know sheeeeeeeite
I just want to correct one common misconception, cast iron does not have a higher stiffness to weight ratio than aluminum alloy.

These values can be found on matweb.com, and are considered 'generic' linear (ie applicable up to yield) properties.

Cast Iron
Modulus of Elasticity (E): 170 GPa (24100 ksi)
Density: 7.2 g/cc (446 lb/ft^3)

Aluminum Alloy
Modulus (E): 70 GPa (10200 ksi)
Density: 2.7 g/cc (168.5555 lb/ft^3)

If you compute the ratios they are

Cast Iron: 23.6 GPa/(g/cc)
Aluminum Alloy: 25.9

However, strength to weight ratios are a very different thing. Often strength is defined as being the stress at 2% strain. This value varies wildly based on the particular alloy. There are actually aluminums that have far higher strengths than some steels, but they're failure occurs at relativly low strains (6%) whereas some steels can go to 33% strain before failure.
no aluminum block 4.6,just heads,cobra is only one with aluminum block,and with the supercharger now,the block is cast iron.
Well, I have the cast iron block in my '97 and my '99. As far as how that affects oil heating and cooling versus aluminum blocks?

I know the Explorers get an aluminum block 4.6, and the aluminum block has been in some mustangs. Why they went to the Aluminum block in the F150's in '03 is beyond me.

So I guess I really have no good input on the topic - sorry to disappoint!
Ray, Thanks I feel much better now!
Though I haven't heard of too many 4.6L's with leaking head gaskets, most are the 5.4L ones. The few 4.6L's that did leak were the 2001 and before ones with the iron block. Also if both the head and block are the same material would they not expand at the same or similar rate, thus causing less of a strain on the head gasket versus an aluminum head and iron block expanding at different rates? Besides if some expensive high performance engines are all aluminum then I would think they can take the stress from an understressed motor.

Thanks for your thoughtful replies.

While an aluminum head and an aluminum block would tend to expand at the same rate, all things being equal, most of the heat generated during combustion affects the head first. (Remember, the head bolts are not aluminum.) Even if the expansion rate of both the head and block are equal, though, it still doesn't take into consideration that the gasket itself, is a composite with different expansion characteristics, and so is under considerble shearing stresses in operation. Fortunately the engineers aren't idiots, and you can probably expect a long life with your truck engine. Just don't presume that all is hunki-dori with an all-aluminum setup. Unless you're privy to Ford's records of that engine's or or its head gasket failure rate, you really don't know what Ford's reason was for migrating back to a cast iron block. (And, it may just be a cost-cutting measure as reported above...) Like you, I own a vehicle with an all-aluminum engine, too (Hyundai). I advise you to do exaclty what I'm doing: carefully monitor your cooling system and don't cheap out on the antifreeze you choose. It would also be a very good idea to keep your routine cooling system flush and refill on an annual schedule.

[ June 08, 2003, 09:49 PM: Message edited by: Ray H ]
One of the disadvantages of an all-aluminum engine in high-load applications is the extra stress on the head gaskets. I'm wondering whether Ford may have had an unacceptable head gasket failure rate with the aluminum block F-150s and decided to go back to the heavier, but more dimensionally stable iron blocks for that application. That they're coincidentally cheaper to produce probably wasn't lost on the bean counters either.
Just to put you more at ease Whimsey - your take on the anecdotal side of the leakign head gasket issue is dead on. It was more of a 5.4 phenomenon than a 4.6 phenomenon, though some did suffer. Since about 01, there have been very few complaints that I have seen on the issue.

AS far as why they went back to a cast iron block, I am willing to bet it was a cost decision. After the original plans came out for the '04s, it was revealed that the cost to produce it was going to be around a thousand bucks more per copy with little increase in retail price. Not something Ford was going to take lightly on part of the F-series, the overall best selling vehicle in NA and a major profit driver.
In the SAE paper I was reading (See thread, Preventing Sludging in Toyotas), the writers say that,

"A change from a cast iron block to an aluminum block with witha cast iron liner resulted in an oil sump decrease of 4 C. The average bore wall temperatuire decreased by 11 C, and the piston undercrown temperature decreased by 9 C. The heat energy transferred to coolant changed negilibly. "

So one should see a 34 F drop in oil sump temperature with an aluminum block over a cast iron block.
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