Castrol Syntec vs. Mobil 1 Oil

Not open for further replies.
Feb 14, 2004
Yonkers NY
I have a 1995 Mitsubishi Montero with 150,000 miles on it. It is a 3.5 and has been running Castrol Syntec 5W-30 during the winter and 10W-30 during the summer. I have been reading and hearing that Castrol Syntec is not as good as Mobil 1. Also when I remove the cap were you add oil inside and around the cap there is some brown gunk, is that bad? It is in the shop getting some things done on the cooling system now.

PS: How many miles do these cars usually last with that oil and the car has overheated 2-3 times when something was wrong with the cooling system.
I'd recommend you check out a product called auto-rx. I'd use that and then chose an oil based on the conditions and drain intervals you are subject to.
If you are draining the oil every 3-4k and want to continue to do that, there are many good oils to chose from.
The car is just used to get from point A to point B. I drain it every 5,000 miles and when we use it in heavy snow i drain it every 4,000 miles. I will give that AUTO RX a try. I hear MArvel Mystery Oil cleans the slude too.what do you think?
OK, my dad and I have decided we will use AUTO-RX. But I was reading the Intructions and it said we have to use non-synthetic oil during that period and he said that he does NOT wanna do. He wants to continue using synthetic even with teh Auto RX, is that possible?
If you have been using syntec for 150,000 miles stick with it. Mobil 1 is a better oil but both are good. You would have problems by now if the syntec wasnt doing its job.
Yes, It has not given me any problems but I still wanna get rid of the sludge and the varnish in the engine. The problem is that the intructions require you to use Non-synthetic oil and my dad does not wanna put that oil in there, is there anything wrong with using synthetic w/ auto-rx. How many bottles do i need for the montero? The car usually takes 5.5 quarts of oil.

The motor makes a "knocking", pining sound when we start the engine and that is what makes us believe the sludge and varnish is clogging the valves.

OK i do not get this. I will change the oil filter and add one 12 ounce bottle of Auto RX then drive for 1500 miles and then I change the oil and make sure to use non synthetic and then drive it for 2000-300 miles and then rechange it and keep using non synthetic and follow up with a second application? so i need 2 bottles (one per application) and then after add the second bottle drive it for 1000 miles and change the oil and filter again in setp 3(application 2) and then rechange the oil to the oil i was using before? srry for being such a noob

[ February 15, 2004, 08:58 PM: Message edited by: Hpisavage21 ]

Originally posted by Hpisavage21:
OK, my dad and I have decided we will use AUTO-RX. But I was reading the Intructions and it said we have to use non-synthetic oil during that period and he said that he does NOT wanna do. He wants to continue using synthetic even with teh Auto RX, is that possible?

It's not that you CAN'T use synthetics, but it's that the dino and ARx won't "compete" for cleaning duties. My suggestion is to follow Frank's recommendations, even using dino oil, for best results.

Then again, is Castrol Syntec a synthetic oil anyway? Not to open a can of worms, but Syntec is mostly Group III, it's probably within the recommendations to use this oil. BUT......check with Frank at Auto-RX first.........
I used Castrol Synthetic Formula R 5W30 for RX clean as it contains no PAO or ester and ideal for the job. Look for a similar product (there are many) and you'll get a better clean and your dad will still be happy.
I convinced my dad and he will let me use regular dino oil. I will use 10w-30 in the summer. The car holds 5 1/2 quarts so i will use 4 1/2 of regular dino oil and one 12 oz of ARX and run it for 1500 miles, then rechange the oil and filter and "rinse" w/ again regualar Mobil Dino oil (5 1/2 quarts) and then run it for 2000-3000 miles and then switch back to synthetic.

whats the best DINO oil?
Best dino oil? There's lots of good ones out there, but Chevron/Havoline leads the way with its low price point, Pennzoil, or simply stick with the Castrol name using the GTX product.

Yes, you'll need two bottles of the A-Rx for your treatment....
2 bottles since its over 100,000 miles right? 1 bottle per application right? The DINO oil will not affect the engine right?
You're correct. 1 bottle per application. No, the dino won't harm the engine, just help Auto-Rx do it's job.

I just finished up a cleaning cycle on my Saturn and decided on Mobil 1 with a 3oz maintenance dose of ARx. Car runs great---smoother ide and gas mileage jumped 2MPG after just one full-bottle treatment. AutoRx is good stuff. Oh yeah, don't forget to warm the bottle up to room temperature prior to adding it to your crank case.
Thanks so much. I am going to head over to Kmart and get some Mobil 10w-30 tomorrow and then a case of Mobil 1 AFTER im done. I was using teh Castrol syntec but ima use the Mobil 1 now.
Im gonna need 22 quarts of oil right? Since Its two applications
22 quarts of dino
5 oil filters

2 bottles ARX

5 1/2 quarts of sythetic once im done right? this is right?

[ February 15, 2004, 10:57 PM: Message edited by: Hpisavage21 ]
Ahh, that valve noise at idle, I've heard that on a couple of Mitsubishis including my brother's '00 Eclipse V6 engine, which I believe is related to your Montero's V6.

I solved it with Mobil 1 oil and an ACDelco oil filter (PF1127 I think, double check to make sure) When I tried a Wix oil filter the noise came back. Valves were noisy using a Mitsubishi oil filter too.

Definitely try the ACDelco oil filter... I guess it flows better.

As for dino oil for the Auto-Rx, just use whatever name brand is on sale...
Thanks, yup the motor kind of "squeaks" at idle which is odd. I will run 2 does of AUTO RX and then switch from Castrol Syntec to Mobil one and change filters to ACDelco. I will also add 3 oz. of auto RX AS a maitmence dose.
Not open for further replies.