Synthetic Oil, Hesitation ?

[LexChamp]

95 LS 174,000

Recently switch to Mobil 1 10-W40 Synthetic Oil. I’ve had the car several months and do not know what type of oil was used before. The first couple of months I had the car I never felt the car hesitate after a stop. After changing the oil, a few days later, I noticed the car has been hesitating. Sometimes after a stop, but now is doing it more often, practically every time I start the car and begin driving. The hesitation comes after pressing the gas; the car hesitates, than makes a big jump, than it goes as normal. The hesitation mostly comes when putting the car in drive and driving.

Has this has anything to do with the SYNTHETIC OIL. I am thinking of going back to what the manual recommends, 5W 30. Any suggestions will be appreciated.

[Cory]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

[LexChamp]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

Hot conditions, not at all. I’m in CT, winter is brutal out here. We don’t have does long hot summers out here. That’s what I was thinking, changing back to at least 5W 30. But, do you think the Synthetic Oil has anything to do with it ? I was thinking of going regular oil.

[djspawn00]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

Hot conditions, not at all. I’m in CT, winter is brutal out here. We don’t have does long hot summers out here. That’s what I was thinking, changing back to at least 5W 30. But, do you think the Synthetic Oil has anything to do with it ? I was thinking of going regular oil.

I seriously doubt the oil has anything to do with it... when was the last time you cleaned the throttle bodies?

[LexChamp]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

Hot conditions, not at all. I’m in CT, winter is brutal out here. We don’t have does long hot summers out here. That’s what I was thinking, changing back to at least 5W 30. But, do you think the Synthetic Oil has anything to do with it ? I was thinking of going regular oil.

I seriously doubt the oil has anything to do with it... when was the last time you cleaned the throttle bodies?

I've had the car for about 4 months, I don’t know if it has been previously done. Like I said before changing the oil, the car was fine. Honestly, I do not even know what the throttle bodies are. Please elaborate

[pishta]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

Hot conditions, not at all. I’m in CT, winter is brutal out here. We don’t have does long hot summers out here. That’s what I was thinking, changing back to at least 5W 30. But, do you think the Synthetic Oil has anything to do with it ? I was thinking of going regular oil.

I seriously doubt the oil has anything to do with it... when was the last time you cleaned the throttle bodies?

I've had the car for about 4 months, I don’t know if it has been previously done. Like I said before changing the oil, the car was fine. Honestly, I do not even know what the throttle bodies are. Please elaborate

That sounds like a classic ignition problem, I would replace your plugs with some Platinum ones (OEM) and check the resistance of the plug wires and the 2 coil wires, none should spec out over 25k Ohms with an ohm meter. Since you dont know what a throttle body is (its the coke can looking thing coming off the left side of the shiny thing on top of the motor...) I would recommend a shop do the plugs. Im very familiar with motors and it took me about 90 minutes to replace the plugs and check the wires as there are a miriad of covers and intake items that need to be removed. Have them put a can of carb/throttle body cleaner through it when they have the intake tube off for the plug replacement.

[LexChamp]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

Hot conditions, not at all. I’m in CT, winter is brutal out here. We don’t have does long hot summers out here. That’s what I was thinking, changing back to at least 5W 30. But, do you think the Synthetic Oil has anything to do with it ? I was thinking of going regular oil.

I seriously doubt the oil has anything to do with it... when was the last time you cleaned the throttle bodies?

I've had the car for about 4 months, I don’t know if it has been previously done. Like I said before changing the oil, the car was fine. Honestly, I do not even know what the throttle bodies are. Please elaborate

That sounds like a classic ignition problem, I would replace your plugs with some Platinum ones (OEM) and check the resistance of the plug wires and the 2 coil wires, none should spec out over 25k Ohms with an ohm meter. Since you dont know what a throttle body is (its the coke can looking thing coming off the left side of the shiny thing on top of the motor...) I would recommend a shop do the plugs. Im very familiar with motors and it took me about 90 minutes to replace the plugs and check the wires as there are a miriad of covers and intake items that need to be removed. Have them put a can of carb/throttle body cleaner through it when they have the intake tube off for the plug replacement.

Here are a few of the suggestions Member from another forum had regarding my problem:

Oil alone will not cause a hesitation. There is no way. You are confusing cause with coincidence. On a side note, why are you running a 40-weight oil? The engine specifies either 10W30 or 5W30, depending on the climate.

__________________

1995 LS400 Gold/Tan

(My Response)

You might be right, about cause with coincidence. Like I said the car had been running fine before the oil was changed. Someone in another forum mentioned if the throttle bodies had been cleaned? Could this be a reason ?

Why 10 W 40, actually a mechanic recomeded this oil because the size of the engine. I know, it makes no sence now that I think about it. I already had several people suggest to change to Synthetic 5W 30 or 10 W 30 as you suggested as well. Thanks

Your mechanic sounds somewhat unintelligent to suggest a particular weight of oil because of an engine's size. If you just cleaned your throttle body, that could have an effect, or even just for other reasons. The throttle plate could be sticking, or there could be an issue with the throttle position sensor.

__________________

1995 LS400 Gold/Tan

go and switch to 5w-30, then go and reset ur ECU by pulling the neg. battery cable for a couple mins OR puling the EFI fuse.

__________

PureDrifter

First, it’s not a good idea to switch to synthetic at such high mileage as you will likely deal with leaks that the lower viscosity of the oil will seep through, switch back! This leads me to believe that the hesitation you’re experiencing is in fact related to the synthetic oil. How?? I would be willing to bet that the synthetic oil has started to leak around the sparkplug seals and is in fact shorting the sparkplugs and leading to the noted hesitation. Remove the sparkplug boots on top of the plugs and look inside to see if you find oil inside.

________

Alsalih

Well at that high mileage it is not good to go to synthetic oil if it has never been used before. The car might start getting a lof of leaks due to switching oil but that has nothing to do with hesitation. My suggestions:

Seems like your car is misfiring so check:

1) cables

2)spark plugs and

3)maybe you have a bad fuel injector.

HIGHLY unlikely. The sparkplug wire boots fit with an airtight seal around the spark plugs.

__________________

1995 LS400 Gold/Tan

Sonyman, I’m not talking about the sparkplug wire boots, I’m referring to the spark plug seal that seals between the valve cover and the sparkplug. If you remove your valve cover you’ll see what I’m talking about.

go take the plug wires out and see if there is oil there, if there is it means the seals are failing.

its relatively unlikely that ur going to bust a seal running 10w40 synthetic, 5w MAYBE but ud be safe with 10w.

LexChamp

I changed my oil today back to Mobil 5W 30 (Non Synthetic) I drove it around the block and it did not hesitate or misfired. I did not get a change to drive it a few blocks. Tomorrow, I will drive it for a while and post the results. Furthermore, I will also check the wires in the next couple of days to check if there is oil in the plugs. I’m going to have to change the plugs and wires in the near future anyway.

Thanks to all who responded.

[LexChamp]

After a while, your engine becomes accustomed to a certain weight of oil. I would suggest switching to Mobil1 5w30 Synthetic, unless you frequently drive in really hot conditions.

Hot conditions, not at all. I’m in CT, winter is brutal out here. We don’t have does long hot summers out here. That’s what I was thinking, changing back to at least 5W 30. But, do you think the Synthetic Oil has anything to do with it ? I was thinking of going regular oil.

I seriously doubt the oil has anything to do with it... when was the last time you cleaned the throttle bodies?

I've had the car for about 4 months, I don’t know if it has been previously done. Like I said before changing the oil, the car was fine. Honestly, I do not even know what the throttle bodies are. Please elaborate

That sounds like a classic ignition problem, I would replace your plugs with some Platinum ones (OEM) and check the resistance of the plug wires and the 2 coil wires, none should spec out over 25k Ohms with an ohm meter. Since you dont know what a throttle body is (its the coke can looking thing coming off the left side of the shiny thing on top of the motor...) I would recommend a shop do the plugs. Im very familiar with motors and it took me about 90 minutes to replace the plugs and check the wires as there are a miriad of covers and intake items that need to be removed. Have them put a can of carb/throttle body cleaner through it when they have the intake tube off for the plug replacement.

Here are a few of the suggestions Member from another forum had regarding my problem:

Oil alone will not cause a hesitation. There is no way. You are confusing cause with coincidence. On a side note, why are you running a 40-weight oil? The engine specifies either 10W30 or 5W30, depending on the climate.

__________________

1995 LS400 Gold/Tan

(My Response)

You might be right, about cause with coincidence. Like I said the car had been running fine before the oil was changed. Someone in another forum mentioned if the throttle bodies had been cleaned? Could this be a reason ?

Why 10 W 40, actually a mechanic recomeded this oil because the size of the engine. I know, it makes no sence now that I think about it. I already had several people suggest to change to Synthetic 5W 30 or 10 W 30 as you suggested as well. Thanks

Your mechanic sounds somewhat unintelligent to suggest a particular weight of oil because of an engine's size. If you just cleaned your throttle body, that could have an effect, or even just for other reasons. The throttle plate could be sticking, or there could be an issue with the throttle position sensor.

__________________

1995 LS400 Gold/Tan

go and switch to 5w-30, then go and reset ur ECU by pulling the neg. battery cable for a couple mins OR puling the EFI fuse.

__________

PureDrifter

First, it’s not a good idea to switch to synthetic at such high mileage as you will likely deal with leaks that the lower viscosity of the oil will seep through, switch back! This leads me to believe that the hesitation you’re experiencing is in fact related to the synthetic oil. How?? I would be willing to bet that the synthetic oil has started to leak around the sparkplug seals and is in fact shorting the sparkplugs and leading to the noted hesitation. Remove the sparkplug boots on top of the plugs and look inside to see if you find oil inside.

________

Alsalih

Well at that high mileage it is not good to go to synthetic oil if it has never been used before. The car might start getting a lof of leaks due to switching oil but that has nothing to do with hesitation. My suggestions:

Seems like your car is misfiring so check:

1) cables

2)spark plugs and

3)maybe you have a bad fuel injector.

HIGHLY unlikely. The sparkplug wire boots fit with an airtight seal around the spark plugs.

__________________

1995 LS400 Gold/Tan

Sonyman, I’m not talking about the sparkplug wire boots, I’m referring to the spark plug seal that seals between the valve cover and the sparkplug. If you remove your valve cover you’ll see what I’m talking about.

go take the plug wires out and see if there is oil there, if there is it means the seals are failing.

its relatively unlikely that ur going to bust a seal running 10w40 synthetic, 5w MAYBE but ud be safe with 10w.

LexChamp

I changed my oil today back to Mobil 5W 30 (Non Synthetic) I drove it around the block and it did not hesitate or misfired. I did not get a change to drive it a few blocks. Tomorrow, I will drive it for a while and post the results. Furthermore, I will also check the wires in the next couple of days to check if there is oil in the plugs. I’m going to have to change the plugs and wires in the near future anyway.

Thanks to all who responded.

95 LS 174,000

I drove the car today for a while and I noticed a big difference since I went back to the 5W 30 (Non Synthetic Oil) There were a few hesitations but not as many as before. The car is definitely running a lot better, with far less misfires. I honestly feel the Synthetic Oil had a lot do with the hesitation and misfire and overall performance of the vehicle.

[daffy]

Hi LexChamp,

I switched to synthetic oil(5w-30) on my 1991 Ls400 at 115,000 miles on the odometer. I did not have a single problem doing this. I am now at close to 307,000 miles it still runs like the day I bought it. Shortly after the transition, I cleaned out the throttle body, because it was very dirty when I looked inside the throat (mostly from the previous oil and possibly how the previous owner drove it). I have not touched the throttle body since. The car does not burn anymore oil than the day I bought it. I really can't see how oil would effect the way a car runs, unless you put the wrong weight of oil in. A Lexus motor is built to very close tolerances and that is why it needs very thin(low viscosity) oil. Your hesitation could be anything else, but not oil(heavy oil may have some effect here, and is not good for a Lexus motor!). I have not had any repair work on my engine except for spark plugs & wires, timing belt, waterpump. The usual stuff. Just my 2 cents worth. Daffy

[aussiels400]

Hey guys, im new to this fourm im also along way from the US as i live in Perth Australia. Ihave a LS400 that i have just purchased a week ago, so i thought id change the oil, filters, and all that other stuff you do when getting a new car, i also used synthetic but it was a 10w 40 that was recomended in the mobil catalog(gets hot here in perth 40+ celsius in summer and not much below 18c in winter).

After my first drive it felt way better than before heaps more responsive and lively and quieter aswell. as long as you use the correct spec oil it shouldnt make your car run worse.

Cheers Tony