Switching to synthetic oil with exisiting leak - OK?

N

NissanMaxima

Joined
Oct 21, 2015
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399
Location
Colorado
Hello all,
I'm loving this 2005 used V6 Highlander I got earlier this year. It had an impeccable car fax with regular oil changes - but most likely conventional oil. There is a small leak from the front valve cover gasket, and perhaps the rear as well. I immediately changed the oil and put in Valvoline MaxLife synthetic blend (red jug) based on high praise on this forum in many posts - thinking that the seal conditioners could help with the small gasket leak, and a blend would be safe considering it had a regular diet of conventional. And, by the way, it does seem to have helped a bit with the leaks. Now I'm wondering about switching to full synthetic MaxLife. I believe the consensus on this forum is that switching to synthetic doesn't cause leaks when none exist in the first place, BUT what about the situation where there is an existing small leak? Valvoline tells me their full synthetic version of MaxLife has even more cleaning power (I like that), but I don't want to risk worsening any leaks. At some point I do need to change the front and rear valve cover gaskets but its a ambitious undertaking and need to wait until spring rolls around again. I'm also intrigued by their Restore and Protect product but they tell me it doesn't have the same level of seal conditioners as the MaxLife line of products.
 
How many miles and how much is it leaking?

It may make already old/leaking seals worse- I’m guessing the VC gaskets are original
 
Car has 125k miles on it and when parked, I only observe perhaps 2 or so drops overnight. After my first oil change using the MaxLife blend, car has perhaps lost no more than 1/8 of a quart at best over a 2k+ mile interval now. I do understand you can't use a motor oil to truly fix a leak long-term. My question is if a full synthetic will make it worse before I have the chance (and ambition) to do this job. I am also asking if a full synthetic in general has more detergents to clean up any exisitng sludge from possible inferior oils used by the previous owner - although most jobs were done at Toyota dealers who probably are using quality oils, even if just conventional oils.
 
The valve cover gaskets should respond to seal swellers in engine oil, but the gasket isn't "soaked" in oil like a crank seal may be.

I would expect a very limited effect.

ka9mnx said:
Most valve cover gaskets now are made from silicon and the only fix is replacement.
Click to expand...
You're thinking of RTV.
 
Last edited:
NissanMaxima said:
Car has 125k miles on it and when parked, I only observe perhaps 2 or so drops overnight. After my first oil change using the MaxLife blend, car has perhaps lost no more than 1/8 of a quart at best over a 2k+ mile interval now. I do understand you can't use a motor oil to truly fix a leak long-term. My question is if a full synthetic will make it worse before I have the chance (and ambition) to do this job. I am also asking if a full synthetic in general has more detergents to clean up any exisitng sludge from possible inferior oils used by the previous owner - although most jobs were done at Toyota dealers who probably are using quality oils, even if just conventional oils.
Click to expand...

Might try Valvoline Restore & Protect Synthetic if you are trying to do some cleaning. Some have had positive results with it and it's still under $30 at WM per 5 qt.
 
NissanMaxima said:
Car has 125k miles on it and when parked, I only observe perhaps 2 or so drops overnight. After my first oil change using the MaxLife blend, car has perhaps lost no more than 1/8 of a quart at best over a 2k+ mile interval now. I do understand you can't use a motor oil to truly fix a leak long-term. My question is if a full synthetic will make it worse before I have the chance (and ambition) to do this job. I am also asking if a full synthetic in general has more detergents to clean up any exisitng sludge from possible inferior oils used by the previous owner - although most jobs were done at Toyota dealers who probably are using quality oils, even if just conventional oils.
Click to expand...

Fix the leaks, magic tricks won’t help the underside being puked on.
 
Unlikely full synthetic Maxlife will make any difference one way or a other over a few months until spring. Pick a nice day and swap the easy front gasket you can see leaking. You will get an idea if it is sludged up or not and gain confidence to do the other.
 
BC1 said:
Unlikely full synthetic Maxlife will make any difference one way or a other over a few months until spring. Pick a nice day and swap the easy front gasket you can see leaking. You will get an idea if it is sludged up or not and gain confidence to do the other.
Click to expand...
Absolutely the right answer. You also need to have an oil change schedule that will help clean this engine out. Plus, when changing the gaskets, you get a magical opportunity to see what the engine looks like inside and maybe even do mechanical cleaning. I would do a Liqui moly flush, sacrificial flush, get a good filter even a Toyota all immediately after the valve cover gasket, and run a good synthetic for 4K miles on your barely broken in car. Good luck. Maybe 3k to get going. Start watching The Car Care Nut.
 
The Critic said:
The valve cover gaskets should respond to seal swellers in engine oil, but the gasket isn't "soaked" in oil like a crank seal may be.

I would expect a very limited effect.


You're thinking of RTV.
Click to expand...
No. Valve cover gaskets are submerged in oil when running.

No. Not thinking of RTV. The valve cover gasket and pan gasket in my '93 4.9l are silicon. DO NOT over torque!
 
Ayrton said:
If you aren't going to fix the leak soon, I'd stick with the regular Maxlife and do regular oil changes.
Click to expand...
This. Don't switch to synthetic until you change the gaskets, and maybe not even after that. I don't care what people here say, I have first-hand experienced full synthetics "finding" leaks in older cars.
 
TomYoung said:
Absolutely the right answer. You also need to have an oil change schedule that will help clean this engine out. Plus, when changing the gaskets, you get a magical opportunity to see what the engine looks like inside and maybe even do mechanical cleaning. I would do a Liqui moly flush, sacrificial flush, get a good filter even a Toyota all immediately after the valve cover gasket, and run a good synthetic for 4K miles on your barely broken in car. Good luck. Maybe 3k to get going. Start watching The Car Care Nut.
Click to expand...
Why are we so keen on "cleaning this engine out"? If it had regular oil changes, which records show it did, then it's likely fine as-is.
 
BC1 said:
Unlikely full synthetic Maxlife will make any difference one way or a other over a few months until spring. Pick a nice day and swap the easy front gasket you can see leaking. You will get an idea if it is sludged up or not and gain confidence to do the other.
Click to expand...
^^^^^ this, IMO.
@NissanMaxima you might be trying to solve a problem that doesn't exist (sludge / build-up). If the vehicle had regular changes then it's probably pretty clean regardless if it had conventional oil in it.

Just my $0.02
 
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