Dirty oil causing hard starts?

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I've had an issue with intermittent long cranks/hard starts. When the car eventually starts the RPMs are lower than they should be until I press on the gas a bit.

Recently, I've changed my engine oil to 5w30 Castrol Extended Performance and the hard starts went away.

My previous oil was 5w30 Dexos 1 Gen 2 Castrol Edge Black Bottle API SP rated (also ACEA A5/B5 rated) , it's been in the engine around 11 months and had less than 7k miles on it. There were around 5.5 quarts when I drained the oil out, so it wasn't too low.

Why would the old oil cause long cranks, hard starts, and low RPMs on startup? Had anyone else experienced something like this?
 
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Doubt it. Things that could cause hard starts include (but are not limited to) dirty injectors, dirty intake/throttle body, worn or fouled spark plugs (or bad coils), vacuum leaks or faulty AFR sensors, bad camshaft position sensor, or bad crankshaft position sensor. You really need a scan tool that can read and graph live data to quickly determine what isn't right and might be the culprit.

Excessively thick oil at very low temperature may cause a slightly longer, "heavier" sounding crank but it's generally hardly noticeable. Most modern engines will start right up so long as the oil can be pumped. RPM is computer controlled, if the ECU sees the rpm at 500 and it really wants 750 it will just crack open the throttle more and add fuel until it achieves this, it will then store the mapping as learned, that's why some cars idle like crap after a battery replacement first few minutes.
 
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I've had an issue with intermittent long cranks/hard starts. When the car eventually starts the RPMs are lower than they should be until I press on the gas a bit.

Sounds like whatever your engine has for an idle air control valve is gummed up or not working right. Oil has nothing to do with that.
 

SwedeSammy

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no.

Something else is going on. Oil doesnt cause hard starts or cure them.
My issue got better with the fresh oil change. If the hard starts come back, I'll update my post.
 
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2007 Volvo V70 2.5t
A car or at least engine platform many of us are very familiar with (see my avatar).

Oil is in no way causing that. You didn't provide very basic stuff for a question that is necessary - mileage, climate/location, and service history. Give some of that and we may be able to neck it down. If it's got over 125k miles on it and you've never replaced the TCV and checked the hoses, that could be it. But it's not the oil.
 

SwedeSammy

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A car or at least engine platform many of us are very familiar with (see my avatar).

Oil is in no way causing that. You didn't provide very basic stuff for a question that is necessary - mileage, climate/location, and service history. Give some of that and we may be able to neck it down. If it's got over 125k miles on it and you've never replaced the TCV and checked the hoses, that could be it. But it's not the oil.
I'm the 3rd owner, car has 108k miles. I don't know whether the TCV was ever replaced. I didn't even know that this part can affect startup.
 

SwedeSammy

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I'm the 3rd owner, car has 108k miles. I've had it since 99k miles. I don't know whether the TCV was ever replaced. I didn't even know that this part can affect startup. Climate now is beach area but it was happening since I was located in a city environment last year. Previous owners had meticulous maintenance records but they're not in English. I'm guessing that I need to do a smoke test to see if there is a vacuum leak somewhere? The vacuum hoses that are visible look like they're in good shape, flexible and not hard or cracked.
 
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I'd so no, unless the oil was as thick as 80W-140 gear oil after missing several OCI's and it was cold out.
 
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SwedeSammy

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Oil was 11 months old with a little less than 7k miles. This issue happened intermittently in all kinds of whether (basically all seasons) and also for both hot and cold starts

There is no check engine light or stored codes either. So it has been tough to track down the problem.
 
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Oil was 11 months old with a little less than 7k miles. This issue happened intermittently in all kinds of whether (basically all seasons) and also for both hot and cold starts

There is no check engine light or stored codes either. So it has been tough to track down the problem.
Intermittent is the operative word, meaning it doesn't happen all the time. So changing the oil is no guarantee that the oil change fixed it, I'd call it a coincidence. It wouldn't surprise me if there's a mechanical issue and it happens again.
 
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I'll say it appears the long start and low idle are together hand-in-hand as maybe one issue. It could be taking long to start because to idle is too low?
 

SwedeSammy

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I'm the 3rd owner, car has 108k miles. I don't know whether the TCV was ever replaced. I didn't even know that this part can affect startup.
I'm the 3rd owner, car has 108k miles. I've had it since 99k miles. I don't know whether the TCV was ever replaced. I didn't even know that this part can affect startup. Climate now is beach area but it was happening since I was located in a city environment last year. Previous owners had meticulous maintenance records but they're not in English. I'm guessing that I need to do a smoke test to see if there is a vacuum leak somewhere? The vacuum hoses that are visible look like they're in good shape, flexible and not hard or cracked.
 

Astro14

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Several potential causes for hard starts in that car.

Dirty throttle body
Failing crank position sensor
Failing cam position sensor

So, clean the throttle body first. Also, you should check the PCV system. On that car, they get filled with gunk and oil and cause other problems, like dirty throttle bodies, and ultimately, blowing out cam seals. Might be worth doing the PCV system.

A bunch of oil in the intake, from a failed/failing PCV system, can cause hard starting.

Dirty oil didn’t cause the problem. Changing the oil hasn’t fixed the problem.
 

Astro14

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Don’t laugh - this actually happened on my wife’s XC - poor idle and hard starting.

PCV system was in good health. But she drives gently. The engine intake tract had oil from the PCV system, causing stumbling at idle, and hard starting, because it was never pulled through the engine at high RPM/boost.

I cleaned the throttle body, changed the oil, then took it out for a drive. A couple of full throttle acceleration runs and the car had visible exhaust. Not really smoke, but enough exhaust to see in the mirror. By the third run that smoke/exhaust was gone.

And so was the stumbling idle.
 
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