Intermittent Oil light when car turns on

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Apr 14, 2020
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Hi I got a 4.0 mustang a few months ago. It came with an orange can fram and black oil. I filled supertech hm synthetic and a st filter. After about 1000 miles I noticed the oil light on a second or two after startup. Oil was pretty dark for 1k. I changed to penzoil platinum hm and a fram ultra. No more oil light. 1000 miles later it is doing it again. Oil level is correct throughout. Is it reasonable to assume the oil light means my filter is clogged with sludge and needs to be changed, or is there some other explination?


I asked my car buddy and he said to ask you guys.
 
Sounds like the oil passages in your engine is sludged up and it's being slowly broken up into the oil over the 1000mi each time, might not be a terrible idea to do a pan drop and see if there's any sludge down there and if there is clean it up to reduce sources of sludge, and either keep doing what you're doing until the oil comes up clean or you can look into running some flushes through the engine,
 
If you are going to seriously tackle it and do a pan drop, also do the valve covers.

You choice of PP is one of the best you could chose to clean up the insides of an engine. In fact it might be easier to start with which ever valve cover is the easiest to do to get an idea of whether or not it looks like doing the the pan and other cover might remove enough buildup to be worth doing it.
 
Last edited:
2007 4.0 v6 mustang. 210k miles.

I have a few different engine flush products you idle 10 minutes before a change. Also a cleaning additive that suggests to keep the entire change (stiction eliminator). I'll try using both those when I change the oil again tomorrow.

Penzoil platinum may have more detergents, but is it really worth $8 more than supertech when I am doing a change every 1k? Same with filter capacity, fram ultra and an extra $5?


Are there other symptoms I should look for if it is indeed passage sludge?


I have done a transmission pan drop before, but never an oil pan. Can't think of any reason it would be more difficult.
 
Originally Posted by Infomercial
I have done a transmission pan drop before, but never an oil pan. Can't think of any reason it would be more difficult.


Access. Trans pan is expected to be dropped regularly. Oil pan may have something in the way under it making removal difficult.
 
It is the red oil light like a lamp. I believe it is a low pressure light. It is only on a second or two after cranking.


Would I really not be almost as well off in this situation just changing the filter and topping off?
 
Originally Posted by Infomercial
2007 4.0 v6 mustang. 210k miles.

I have a few different engine flush products you idle 10 minutes before a change. Also a cleaning additive that suggests to keep the entire change (stiction eliminator). I'll try using both those when I change the oil again tomorrow.

It is the red oil light like a lamp. I believe it is a low pressure light. It is only on a second or two after cranking.

Would I really not be almost as well off in this situation just changing the filter and topping off?


If your engine really is sludged (and to an unknown degree) I would not use either the engine flush or stiction eliminator at this time. You've got nothing to lose by putting on a new oil filter and topping off the oil. No need to use a Fram Ultra. On a side note, what oil weight are you using?
 
Stick with inexpensive synthetic (or semi-synthetic) and a $4 filter for now, every 1,000 miles.
If things don't get better after 3 more oil changes, I fear you may have a plugged oil pickup screen, and no "flush" will really help with that.

You can try.....but - - -

Oh, and do the flush stuff into the old oil at the very end part of the oil change interval,
and NO aggressive driving if the flush is in the oil.
 
The oil pressure light is run by a switch that is grounded out (so the light goes off) when the oil pressure goes above 7 psi or so. If the light is staying on a little longer than usual, it's more likely that the anti-drain back valve in the oil filter is letting all the oil in the engine drain back into the oil pan than because the filter is clogged. Try using a Motorcraft filter next time. They're available at Walmart and have a better quality silicone anti-drainback seal.

As for worries about sludge, what does it look like if you shine a flashlight down the oil filler tube? If you don't see lots of gunk built up, you're probably OK. If you want to get the engine cleaner inside, personally, I would do a few more short change intervals like you've been doing with cheap oil and then switch to a 5K miles schedule.
 
IDK, the oil light staying on for a second/two, doesn't sound abnormal to me. I mean, I've had engines that did this for their whole(200K mile) life.

Do you hear any start-up rattles/noises?
Does the light stay on(1-2 sec) anymore during the day, meaning other start-ups?
 
I would continue to do the 1000 oil / filter changes if the oil continues to come out very dark at 1000 miles .

Check rockauto.com for less expensive , but good filters . I ORDER 6 TO 12 AT A TIME TO HELP SPREAD OUT THE FREIGHT COST PER EACH .

Sorry about the caps ! :-0
 
I didn't bother reading all the comments, but you'll want to check with a gauge before tearing into the thing. It could just be the sensor.
 
Like the last poster said.... Check the oil pressure switch. While this could be signs of bad stuff in the engine, neglect also seems to sometimes plug up the oil pressure switch. So it should be the first thing to be checked. Other than that, keep doing what your doing. A few 1000 mile changes with whatever is cheapest on sale, and hopefully that cleans things up some. Then gradually increase to a normal oil change interval.
 
All good advice. Let's sum up with the plan to replace the oil pressure switch and run the inexpensive oil and filters. ST High mileage and ST filters come to mind all available at Walmart. Change the sensor and oil and monitor. Don't go aggressive with engine flushes yet.
 
I would also change the oil pressure switch that turns on the light. It may also be gunked up. It has no flow through it so it will never clean up.
 
Just an update nearly a year later:


I just got the light after 3500 miles on mobil 1 AP and a Purolator boss, longest run yet.

Changed the filter to try to buy some time until it is warmer out and that mobil1 is black, very dark brown wiped off the dipstick.

I'll probably change to supertech full syn and a wix xp over the weekend. I'll be very happy with another 3500 mile run. I intend to go no further than the 5000 mile oci in the original manual.
 
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