Why High Mileage Oils?

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dsmith41

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I don't understand what the point of a "high mileage oil" is. What do they do that any other quality oil can't do, specifically, a quality synthetic?

What does it mean to condition seals? Is it just marketing? Can they really reduce oil comsumption as I have heard? My girlfriend's Impala uses oil and I am going to either do regular Pennzoil YB or Pennzoil HM at next change, can't decide.
 
what year impala? are you losing any coolant? I only ask because most GM's that have the red Dexcool in them are at risk of intake manifold gasket leaks....

seal swell conditioners can swell up seals and gaskets enough to reduce oil consumption. really really.
 
They have higher cleaning detergents usually and detergents meant to condition seals like you said. It's not a miracle worker if you already have a leak but it helps preventing future leaks more so than regular oil. It's not just marketing.
 
It is an 01 Impala and I have heard about the bad intake manifold gaskets but I have not looked at her coolant like I should. I checked it during the summer and it was fine though. I plan on checking and replacing the PCV valve and I guess if these high mileage oils really are legit, I'll give them a whirl as well.

ETA: If you use a high mileage oil with seal swelling additives and then go back to regular oil, can the seals shrink back to the point of causing leaks? Or is that along the same line as the myth that you can't put synthetic in an older car because it will turn the seals into swiss cheese?
 
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I can scarcely believe the amount of negative talk on here about DexCool...but in reality, my experiences with it have been vastly different from the bashing that I've seen on this site. The many people I know who have had, or still have a vehicle which uses DexCool have not experienced any issues with it, either. Certainly, as with anything, there will be failures and issues...but DexCool gets blamed for everything.

There was an issue with bad gaskets made by the gasket manufacturer, as there have been bad head gaskets in Subarus, Chrysler / Mitsubishi, etc...but these intake manifold gasket failures were not specifically related to DexCool itself.
 
Originally Posted By: gmchevroletruck

I can scarcely believe the amount of negative talk on here about DexCool...but in reality, my experiences with it have been vastly different from the bashing that I've seen on this site. The many people I know who have had, or still have a vehicle which uses DexCool have not experienced any issues with it, either. Certainly, as with anything, there will be failures and issues...but DexCool gets blamed for everything.

There was an issue with bad gaskets made by the gasket manufacturer, as there have been bad head gaskets in Subarus, Chrysler / Mitsubishi, etc...but these intake manifold gasket failures were not specifically related to DexCool itself.


It all depends. I have had quite a few vehicles with Dex cool, some it worked fine, others it was a headache. If the car had a pressurized overflow/recovery tank (ala Saturn), it worked fine. In a traditional non pressurized recovery tank system (1997 Chevy truck), it was a nightmare. If even a little bit of air entered the cooling system, it would corrode things instantly. I had rusty coolant and a plugged radiator at 45K miles, all due to a slightly pinched hose leading to the recovery tank. It would push coolant out, but the hose would collapse and not allow coolant back in. GM did cover most of the repairs, but it did leave a sour taste in my mouth on Dex Cool working in all applications.
 
Originally Posted By: wolfc70
Originally Posted By: gmchevroletruck

I can scarcely believe the amount of negative talk on here about DexCool...but in reality, my experiences with it have been vastly different from the bashing that I've seen on this site. The many people I know who have had, or still have a vehicle which uses DexCool have not experienced any issues with it, either. Certainly, as with anything, there will be failures and issues...but DexCool gets blamed for everything.

There was an issue with bad gaskets made by the gasket manufacturer, as there have been bad head gaskets in Subarus, Chrysler / Mitsubishi, etc...but these intake manifold gasket failures were not specifically related to DexCool itself.


It all depends. I have had quite a few vehicles with Dex cool, some it worked fine, others it was a headache. If the car had a pressurized overflow/recovery tank (ala Saturn), it worked fine. In a traditional non pressurized recovery tank system (1997 Chevy truck), it was a nightmare. If even a little bit of air entered the cooling system, it would corrode things instantly. I had rusty coolant and a plugged radiator at 45K miles, all due to a slightly pinched hose leading to the recovery tank. It would push coolant out, but the hose would collapse and not allow coolant back in. GM did cover most of the repairs, but it did leave a sour taste in my mouth on Dex Cool working in all applications.

When I did the head gaskets on the Montana, I used a vacuum with a small hose taped to the end of it to suck about 3/8" Of DexSludge out of the water jacket in the block. This has a non-pressurized recovery tank as well.
 
As said earlier.

They usually have a pretty good additive package.

I would call them seal conditioners. They soften up hardened seals so they can perform as intended.

If you switched back to regular oil the seals could harden up over time again.
 
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Originally Posted By: gmchevroletruck

I can scarcely believe the amount of negative talk on here about DexCool...but in reality, my experiences with it have been vastly different from the bashing that I've seen on this site. The many people I know who have had, or still have a vehicle which uses DexCool have not experienced any issues with it, either. Certainly, as with anything, there will be failures and issues...but DexCool gets blamed for everything.

There was an issue with bad gaskets made by the gasket manufacturer, as there have been bad head gaskets in Subarus, Chrysler / Mitsubishi, etc...but these intake manifold gasket failures were not specifically related to DexCool itself.


I am very familiar with the lawsuit defending G.M. and Dexcool. The coolant does not appear to be the cause of the failures. As you said is is not coolant, but the cause is not really bad head gaskets but poorly designed and engineered head gaskets. They were the wrong design and material for this motor and the newer design incorporates the correct metallic sandwich design. The other factor is the design of the intake itself. The gaskets are split which means they are almost impossible to install correctly. Ask any mechanic how fun the lowers are to get in correctly.
In any case , they all fail early and should be replaced because if you leave them it will cause catastrophic engine failures especially on the 3.8.
That said , high mileage oil is worthwhile in some oil burning situations but first the motor should be fixed mechanically , then cleaned internally with mmo or arx. Then use the hm oil to help the valve seals do their job correctly and slow down other leaks.
 
I, too, had a 97 Chevy pickup with a 350. Lost the gaskets at 65,000 miles or so. Came out on morning and coolant was running down the driveway. Never had a problem with cooling system issues until Dexcool came along.
 
I have seen the high mileage oils work to stop a leak. I had a rear main seal leak on my '97 Dakota. It had Mobil 1 at the time (at least according to the previous owner, and their service records did indicate that as well). Valvoline MaxLife eventually stopped the leak. I have no leaks on the truck currently. I'm planning to stick with the MaxLife or Shell Rotella T if I can find it in 10w30 (most is 15w40 around here).
 
Dex-Cool bashing is a national past-time. The pressurized tank idea seems to hold water with me. I've had two Cadillacs, both with pressurized surge tanks, and not a single problem with either. The first one, a '97, is still in the family with 170,000 miles. The second one, an '01, I sold at about 80,000 miles out of family, so don't know how it's doing now. But it was 100% when I owned it.
 
My car has been running Dex Cool for nearly 10 years now and 107,000 miles, and has been flushed 3x total or once every 3.25 years. Not a single problem. I have had other cars that use the fluid and they haven't had a single problem either. Relatives have 3.8L GM cars using Dex Cool and nary a problem.

Must be lucky hah?
 
Originally Posted By: Jason Adcock
Dex-Cool bashing is a national past-time. The pressurized tank idea seems to hold water with me. I've had two Cadillacs, both with pressurized surge tanks, and not a single problem with either. The first one, a '97, is still in the family with 170,000 miles. The second one, an '01, I sold at about 80,000 miles out of family, so don't know how it's doing now. But it was 100% when I owned it.


This has been my experience. I am not Dex cool bashing, but I think it needs to be treated differently than normal coolant. A pressurized recovery tank keeps all possibility of air out of the cooling system, keeping the coolant happy. With a normal system, if the cap becomes marginal, then the radiator does not stay 100% full, causing stuff to corrode and sludge up. Of course leaking gaskets let air in too, so not all of it is the coolants fault. In all my GM vehicles that have/had Dex Cool, the pressurized recovery bottle ones have been 100% reliable.

Ok, back on topic!
 
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I'm trying HM (valvo syn blend) for the 1st time on my 91 pathfinder w/ 185k miles. It just started to develop a leak right between the transmission and motor. I hope it's something small a HM oil can fix...
 
Well because they do not need to be energy conserving or meet any GF-3/4 SM atandards unless they choose too they can make the oil thicker for starter's and this is to improve ring sealing and to fill worn bearing shells better then a thinner oil. Second they can put as much ZDDP as they car to in it as wella s other additives for AW,EP etc........They normaly have a higher amount of seal swelling agents in them and a tad more detergents these are things that a high milage engine might benifit from but would not be needed or even wanted in a normal car with low miles.

For instance the Valvoline Maxlife HM Dex ATF is some of the finest dino ATF onthe market and at a price point that is nice as well especialy if you by the ATF in the 5 quart jugs. It has higher levels of anti-oxidents then most dino ATF's and has been that way since day one. SInce seals in transmissions are almost the heart and soul of an automatic the higher levels of seal swelling agents, detergents,anti-oxidents are great since most transmissions in American vechiles do not get their fluid changed in a timely matter and a lot of them have issues past 100,000 miles.
 
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