Q: I have a couple of friends: one swears by oil additives – especially the brand Lucas – and another claims an oil additive ruined his truck engine. What is your take on oil additives?

A: Some oil additives contain products that change the viscosity of the oil. That can help with oil burning.

Some contain additives that, when mixed with the additive package that comes in a quart of oil, can have disastrous effects. Some additives contain chlorine, which, when combined with other additives, will turn into an acid.

So, to some extent you are playing Russian roulette when you use additives, since you do not know how the additives will react in the oil you are using.

My advice is to change your vehicle’s engine oil on a regular basis, and use the correct grade and weight of oil and a quality oil filter.

2017 Lexus RX-350 has rough starts

Q: Our 2017 Lexus RX-350, with 216,000 miles, is having intermittent starting difficulties. The car stumbles when starting and does not start when first cranking the engine. We also hear that a low pitch exhaust or vacuum leak may be causing the engine to idle somewhat rough. This may be two separate issues. There is no check engine light on the dashboard. We put in a can of a fuel engine cleaner with no success. A local shop did a fuel system cleaning last year. Other than that, this is a great car. Any suggestions?

A: At this point, with the mileage, this could be just a matter of normal maintenance.

At 200,000 miles, the spark plugs should have been changed a couple of times; the fuel filter system may be getting dirty or clogged; or one of the sensors could be outside of its normal range.

Normal wear – or lack of maintenance – can cause drivability issues but won’t always set a check engine light. In addition, if there is a vacuum leak, this could also lead to hard starting. At this point, I would leave your Lexus overnight at a repair shop so they can see how the car starts. Then they can perform a complete scan of the various computer systems as well as a thorough visual inspection of wiring and vacuum hoses.

Battery keeps dying on 2002 Thunderbird

Q: I purchased a 2002 Ford Thunderbird convertible – a car I have always liked. It had 101,000 miles on it and ran great until about two months ago, when we went to California.

We were gone for about a week, but when we returned, the battery on the T-Bird was dead. I had inadvertently left the trunk slightly ajar. My mechanic jumped the car and put in a new battery, but four days later, the battery was dead again. The mechanic put in another new battery, and the car ran OK.

Two weeks ago, we went back to California. I asked my mechanic if I should disconnect the battery, but he said, “Let’s see what happens.” Sure enough, when I returned, the battery was dead again.

Is this a problem with 2002 T-Birds? What could be causing this problem? What can I do to solve it?

A: Start with a test of parasitic drain. Anything over 50 milliamps is considered a problem. The Thunderbird is known for this problem, due to the electronics switches that run everything from the top to the trunk release. I have seen door lock modules, seat modules and alternators all causing parasitic draw.

I have not checked in a while, but I believe if you look at Thunderbird forums, you will find dead batteries to be a common occurrence. This is really a case where you need to test and not guess, since there are too many possibilities that could be the cause of the dead battery.

In the interim, you might want to consider a battery disconnect switch. This way you can disconnect that battery if you are not using the car for a few days.

Battery tools vs. air tools

Q: I do a fair amount of car repairs at home for my family’s aging fleet of vehicles. This could be brakes, tire rotations, oil, other fluid changes, and even the occasional front-end repair. To make life easier, I am considering maybe a power ratchet and impact gun to remove wheels. Are the battery tools as good as the old air tools?

A: Battery tools have improved, with better batteries and brushless motors.

Years ago, I purchased a battery ratchet and it was terrible. Now, even the cheaper ones are surprisingly good.

For some jobs I have found my impact driver with a ¼- or ⅜-inch adapter works well for light disassembly.

For wheel removal you do need decent power. A few years ago, I evaluated a ½-inch wrench from WORX and it was handy, but it just didn’t have the power to remove stubborn lugs.

Recently, I have been testing their heavy-duty ½-inch impact gun. The power is extraordinarily strong (advertised at 1,500-foot pounds) and uses the same style 20-volt battery as my garden tools. My only criticism is that it’s heavy. I would guess close to 9 pounds with the long-life battery.

A few years back, I tried to sell my air tools from when I worked as a professional mechanic. Because of the popularity of battery tools, no one wanted them. I ended up donating them to a local vo-tech school. They were happy to have them.

John Paul is the AAA Northeast Car Doctor. He has more than 40 years of experience in the automobile industry and is an ASE-Certified Master Technician. Write to John Paul, The Car Doctor, at 110 Royal Little Drive, Providence, RI 02904. Or email jpaul@aaanortheast.com and put “Car Doctor” in the subject field. Follow him on Twitter @johnfpaul or on Facebook.

This article originally appeared on The Providence Journal: What is your take on oil additives? | Car Doctor