Synthetic or Castrol GTX High Mileage??

Discussion in 'Fox 5.0 Mustang Tech' started by Kdubslugga, Apr 25, 2004.

  1. I need an oil change and im either gonna get some Castrol GTX High Mileage, or some Royal Purple Synthetic Oil. My car has 135K on it, and its starting to leak oil, not to bad, but after a few days theres a little spot in the garage. What kinda Oil would be best? Ive heard Castrol High Mileage, can sometimes stop leaks, and Royal Purple says it gives you more HP!
  2. I have 141k...still running strong...and I use Valvoline Max Life...and have no leaks...

    I personally wouldn't run full synthetic...
  3. Dont mean to sound like a jerk, but what is your reasoning for not running full synthetic? I have no idea about oil, but i thought synthetic was supposed to be better than regualr oil. Thanks for your input.
  4. ive heard that if u run sythetic its hard on the engine to go back to the regular stuff. personaly i use 20-50 penzoil, works gr8, no problems and my stock 302 is at 233k
  5. Its thinner...more likely to cause leaks...and also I've heard what blkstangman88 stated in Post #4...
  6. Is Castrol GTX High Mileage good oil to use? Is there any other oil thats partially synthetic? I heard a lot of guys like Mobil 1, is that good stuff?
  7. umm quacker state had oil i liked, it was the sythetic blend, it was half and half, that way it wouldnt kill my engine if i could afford it right away...well everywhere here stopped carring it so alwell.......another thing is, every oil is diff. but dont get thin crap.....factorys say put the 10-30 in car, thats only for better gas milage, if u want ur car to last, dont put that thin crap in ur car. for a 5.0 id say put no less then straight 30w in your car, but i like the heavy stuff like 20-50.
  8. I always use Castrol GTX... doesnt seem to leak or burn too much.
  9. Mobil 1 high performance is another good one.....

    also....Lucas heavy duty oil stabilizer....swear by by it...makes any oil better
  10. I have read on here it is not really good to "start" useing synthetic on a high mileage engine. I am not saying it is not good stuff but people have said it can actually cause leaks in an older motor. It is hard on old seals in the engine? I would say use the normal high mileage engine stuff it makes sense(the name) in your case. In other situations I would say synthetic, absolutely.
  11. ive got 400,000 kilomerters on my towncar, ive tried some different oils like the highmilage stuff, used 10w... i liked it it was ok. when my car had a leak i put in a can of stop leak. it stopped the leak. then i changed the oil with full synthetic 5w for the winter. it started up easier and the engine warmed up quicker with the thinner oil. when it burned oil i just toppd it up with semi synthetic because its cheaper. i would never use a thicker oil then 10w. i just feel thick oil doesnt protect as well because thin oil can get places thick oil cant. id rather have my car leak and burn oil than not get the protection. i also love lucas oil additive. its goopy stuff like sap, makes the oil slimeyer. kinda like sugar water as opposed to water. adding the lucas raised my oil pressure out of the danger zone the same day i added it. less steam came out the valve cover breather as well after adding it. ive topped up with the high miles stuff before. if i were you id ad some semi synthetic with the lucas. and i wouldnt go any thicker than 10w.

    edit: oh and the reason why people say synthic isnt good on a high mile engine because it causes leaks is synthetic oil can just get places dino oil cant because its more slippery and lighter. stop leak cans have an oil sludge thats really heavy and will fill the places that oil can leak out.
    if you want even more protection a magnetic oil drain plug can catch particles.

    for more info check this page
  12. yep, it is the detergents in synthetics that can clean out sludge plugging pinhole leaks. syn does not create leaks.
    if a leak is found, that was a seal that should be fixed.

    additives - avoid stuff with teflon. top end does not like that.

    many people have toggled back and forth between dino and synthetics.

    Kevin, you confuse me. you talk about not using a thicker cold weight than 10 SAE, but then talk about loving lucas, which is like molasses. i know you are talkin about a synthetic 10W -XX, but remember most synthetic 15 or 20 weights flow better cold than dino 10 weight. so when comparing to the dino users, it is not apples to apples.

    you have to remember the other side of it. you are right - thin oil does flow better than thick oil. but the flip side is that, when the oil is really hot, and it is flying through your bottom end, which probably has a bit more tolerance than it did when new, you are not giving much protection (cushioning).

    my take: run the thinnest oil you can that maintains decent pressure when fully warmed up.
    for what it is worth, i run 20W-50 9 months of the year. 10-40 does not like 110* ambient temps. my two cents worth.
  13. I do not recomend synthetic on a ho\igh mile engine. You will get leaks as mentioned above and it also cost me a motor once. Somebody mentioned the detergents that clean out the gunk blocking places that oil can leak, well it also does a really good job of lifting any of that brown varnish stuff off the bottom of your oil pan. I had an 80k moter and I went to synthetic and about a week later it lifted the gunk off the bottom of the pan in one big sheet like plastic wrap or something. Well as you can imagine it went straight up the oil pump pickup...bye bye oil pressure and hellow new motor. The end.
  15. Quaker State is owned by Penzoil and Penzoil sucks the big one.

    If you are leaking oil already(make sure it's oil and not your rear main seal!), I wouldn't use synthetic, just make it worse.

    Once you use Max life and the leak stops, the moment you use a regular oil, the leak will be back.

    You can switch back every oil change if you want from dino to synthetic. At the current state of oil as of now it's perfectly fine. They offer blends also...

    If I were you, I would track down the oil leak(probably your oil pan), change the pan gasket and dump in Royal Purple.
  16. stangman..straight 30w oil??? where do you live man? i hope its hot there all the time.
    slugga, i agree with hissin50, the detergents in the synthetic help clean any spots where there is sludge which can cause leaks, or make a small leak worse. the high milage oil has additives in it designed for the wear that has been done in a high milage car, as for the weight, depends on where you live and whether you drive it in winter. if you get cold winters, well below freezing, dont put straight 30w in it, use a 5-30 or 10-30 summer you can get away with a heavier oil like 20-50 but personally i wouldnt where i live.
    there is no difference in the 5-30 and 10-30 at operating temp, they are both 30w then, but if its below freezing the 5w flows faster up into the engine at cold temps, less wear. 20-50 in freezing temp is like molassis.
    if you are in the southern areas where there is little cold you can do it though.
  17. nicely said. i should have said (if i did not), that i live in tucson. it was 90* today. even 20-50 pours like a 10-40 does in a cooler climate. and when im idling in traffic in 110* temps, it makes me feel better.

    i think it is a feel thing. if you run 10-30 and are runnin thin or low on pressure, try 10-40. then jump to 15-50 or 20-50 if the lesser viscosity does not work. my two cents....
  18. when i live in washington its always cold so the 30w is what i awlays put in, and washington is almos tnever hot, but when i moved to AZ i put 20-50 in all the time.
  19. I think Mobil 1 makes the best domestic stuff you can buy. I ran it and never went back. Run it in all my vehicles. It improved gas mileage on My FX4 supercrew 1.5 mpg on the highway
  20. Yeah I used Mobil 1 on my 2000 GT and it was some good stuff...but don't use synthetic on a car with a lot of miles or with a leak...