"High" mileage Intrepid - Switch to syn?

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Mar 28, 2004
Blacksburg, VA

I have a 2000 Dodge Intrepid with 73,000 miles on it. I have treated her well changing the oil every 3000-3500 miles, but I didn't own her for the first 25,000, so I can't vouch for that time.

I realized that she will be crossing 100,000 miles right around the same time I leave graduate school with lots of loans. I need her to last well past that.

In my research I came across a website dedicated to Dodge Intrepids made in 98, 99, and 2000. According to the website the engines in these models has a tendency to crap out right around 100,000 miles, partially due to sludge buildup.

Therefore I am considering switching over to synthetic, but I fear it may be too late to do so. Is 73,000 miles too late? I have read about the Mobil1 high mileage synth formula, would this be an ideal starting point? I know that RedLine is better, but I don't think I can swing $8 per quart.

So, my questions are as follows: Does anyone know anything about Dodge Intrepids from 98-2000? Is it OK to go synthetic after 73,000? What brand should I use? Is there somewhere online to buy this brand cheap in bulk?

Thanks for helping me out. I am a noob and any advice you guys can give would be greatly appreciated.

I think its an old school thought about switching to synthetic. I did this in the last 6months on a 8 yr old (150k) & 9 yr old car (200k) with no issue to Mobil 1. 73k miles is nothing unless driven all city miles and hard.
They are mostly city miles. I spent a couple years of my undergrad living about 2.5 miles from campus and the bus didn't come within walking distance, so I drove that 2.5 miles back and forth at least once per day. It has gotten a decent amount of interstate work, but there's been a lot of city driving too.
Mobil 1 is a very good oil (but not the best) and available the cheapest at Walymart. Companies like Amsoil suggest an engine flush before converting to synthetic oil. Its probably a good idea, however all engine flushes are not alike. Some are kerosene and provide no lubricating properties. If you do go for an engine flush go for one from a known oil company like Amsoil. If you do not go with a flush, your first use of synthetic oil will clean out the majority of the sludge so you might want to change the oil the first time between 3-5K miles.

If you want to save $$ and the environment, then go with Amsoil oil & filters and change the filter at 12.5K and the oil at 25K. The oil is made for that kind of extended oil change.
Not the same car, but I changed my '97 Chevy S10 over at 94k. Did a Seafoam flush, then used Havoline and Supertech synths for 4k each, then switched to Amsoil for a 10k OCI. Midway through the Amsoil right now and have not had any problems.
Sweet, so it sounds like I should be able to do this without any problem. Question: where could I get a seafoam flush done and how much would it cost? What other types of flushes are available and how much do they cost? I get most of my work done at Merchant's Tire. They've always been really nice and have never given me any trouble. I plan to learn to do my own oil changes once I live in a house, but for now it easier to just have someone else do it.

Sorry I have so many questions, I just want to make sure I don't screw anything up.
I think you should inspect under your valve-cover before you commence any flushes. If it is a light black soot or a light varnish, which is possible considering your frequent changes you can skip the chemical flush. Probally, you could switch to a syn for a short oci before going for the final product. WalMart 10w-30 syn has "high miles" seal conditioners, a perfect choice.
Here is what I'd do:
This summer- a HDEO dino 15w-40 or cheap HDEO synth 5w-40 like Rotella to do the cleaning. 5000 miles
Fall- WM HMV 10w-30
Next choice is yours, WM syn is the only I know of with HM seal conditioners. One short
PS I would just stick with dino HM oil in that car. Castrol GTX HM in place of the synth. Not much difference in your application, except cost.

[ March 30, 2004, 10:22 AM: Message edited by: Audi Junkie ]
Do you have any leaks from the engine? If you do, going to syn. would only make the leak(s) worse. I changed over to syn from dino at 61,250 miles with no problems. I know the engine didn't have leaks before I switched. A lot of people will say, if the engine is well maintained then you should have no problem.

Originally posted by SethH:

I have a 2000 Dodge Intrepid with 73,000 miles on it. -Seth

Kind of funny your description, high mileage. The UOA's on my wifes 2001 Impalla showed a downward trend in wear metals indicating it was just about fully broken in by 50k miles.

My Caprice has 243,000 miles so if you have high mileage I am not sure what to call mine. I switched mine to syn when it had 87,000 miles with no problems.

I had a car go over 200k miles using plain old Valvoline and many others have posted similar results with dino.

Now it would be real interesting to see the data on factory dyno endurance tests comparing dino to syn and how much longer the engine lasts.

I mainly use synthetic so I am not under the car every month changing oil.
Almost all synthetics have additives that act to condition seals in any engine. What has happened is that some dino oils have started adding them recently and calling them high mileage oils. Regardless of whether its mentioned on the label or not, the synthetics have it.
If this guy is worried about sludge problems wouldnt it be wise to do a Auto-rx treatment then after thats done switch to synthetics?I have started the auto-rx on my truck and am amazed at the results so far.
V6 Diesel:

I only put the word "high" in there because most oils that are supposedly made for "high mileage" vehicles list 75,000 miles as the starting point for high mileage.

So what is an auto-rx treatment?
If you can look through the oil filler cap at the valvetrain with that engine, do so and this will tell you how much sludge/varnish is present, if any. If it's clean, you can simply continue your current habits. If you want more detergent/dispersant qualities, you can also try a diesel lube (these have very high TBNs, their quantified long-term cleaning capability) or high-mileage oil (these have semi-high TBNs). Either is less expensive than synthetic.
HDEO means diesel-rated oil, usually 15w-40. A fine weight for summer. Chevron Delo 400 also has an SAE 30 monograde HDEO and a 10w-30 if you want it for cleaning. Synth HDEOS come only (mostly) 5w-40s so that is fine for summer and winter. You can stay with that...a HDEO Rotella T Synth 5w-40(@Wal*Mart) would be fine for more cleaning but you will be ok with a M1 5w or 10w-30 oil after a cycle of any HDEO. Dino Mobil Delvac 1300 15w-40 then Mobil 1 (or synthetic Delvac 1 5w-40) would be a fine combo.
Ok, so I think I'm going to go with the Rotella Synth 5w40 for this next rotation and then go with something like the Mobil 1 High Mileage Synth 10w30 or Amsoil after that unless someone tells me this is not a good idea.

When I use the Rotella 5w40 should I go 3000 miles before switching to 10w30 or should I go more or less?

Thanks again for all the help.
Audi Junkie:

Thanks for all your advice. Can you define HDEO for me? I'd really appreciate it (sorry if this is a stupid question). Also, why do you recommend 5w40 to start? I was thinking 10w30 for the summer (for fear of temps going over 100F) and then possibly 5w30 for the winter. Will the 5w40 help to clean things out better?

Thanks again for your advice.
Oh, and also I think I read that the Mobil 1 synthetic has a high mileage formula with a seal conditioner. Would this be better than the Walmart oil?
Everytime I used Rotella in a relatively clean engine, the oil went dirty right away. That being said I would go less than a normal oci. Since Rotella can really go far (high TBN) I would just go all summer, 6 months up to 7500 miles. If you had previously used synth or a HDEO oil, 9000 miles would be fine on the Rotella, but it will get loaded up with your old dirt right away. After using the Rotella for a cleaner, find your most cost/effective synthetic 0w-30 5w-30 or 10w-30 or even the M1 0w-40 depending on climate or an oil with the exact features that you want like long-life more cleaning, seal conditioners or eventually slightly higher viscosity to deal with worn engine tolerences. Saab synth 0w-30 is a Mobil product that is a long-life oil for under $4. Very cost-effective and easy to get.

[ March 31, 2004, 12:27 AM: Message edited by: Audi Junkie ]
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