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Discussion Starter #1
So oil pressure on my ‘91 SE has been running just about vertical on the gauge. Sometimes down to the second white mark at idle (just left of vertical), and then sometimes up to the first white mark after vertical at higher RPMs. I did an oil change a few weeks ago with Castrol Edge Supercar 10w/60 and the pressure has remained consistent on our weekend drives. This includes drives in the mid to high 90s ambient with the AC cranking the whole time.

During a drive this morning (ambient air temp in the 80s) pressure was reading lower than normal. At idle it was almost down in the red, and at full throttle high RPM it never got beyond the second white mark. At 70mph, 2900 RPM on the freeway it was running at the second white mark.

I stopped and verified oil level and it’s still at the high mark on the dipstick and oil still looks brand new. Sitting in traffic a couple of times water temp would creep up just beyond vertical which seemed a bit unusual in these cooler ambient temps, but never got critical and oil temp always stayed at 80 C or below. Never got an oil pressure warning light.

Any ideas as to why pressure would drop off like that and should I be concerned? Pic below is at idle, right around 950 RPMs.

Thanks all,
Eric

1267561
 

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My 87 Turbo Esprit has Smith's gauges, around 25 lbs idle and 50 lbs at 3500 RPM (5th gear at freeway speed). While 4 vs 8 cyl, your pressure does sound low to me.
 

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Wingless Wonder
1988 Esprit Turbo
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First off, Lotus recommended 20W-50 weight for our engines. Oh, and I admire your (non-cracked) wooden binnacle panel!

Here are the specifications for oil pressure:

1267624


If you can trust the gauge, your oil pressure seems at about one bar... minimum is 1/2 bar (edge of the RED mark).

First thing it to crawl into the boot and make sure the crimps on the oil pressure sender are secure. (Ours keeps 'twitching'...has done it for years.)

I forget the mileage on your car, but many owners have needed to replace the oil pump 'innards' (rotor & annulus) and verify the end float & clearance. JAE sells kits.
 

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Discussion Starter #4 (Edited)
Thanks @carbuff. I’ll check the crimps because there’s definitely something that’s changed. I just hit 30,000 miles on the odometer. If crimps are good then I guess it’s on to the oil pump. Though before I get too far into any of this I’ll drain that new oil and replace with some Valvoline VR1 20W/50. I’d read somewhere that many owners had switched to that 10W/60 Supercar stuff, but in cars I’ve owned in the past I’ve actually seen small changes in oil spec make a difference in pressures. Maybe I’ll get lucky.
 

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5 PSI at idle speed? I gotta look tomorrow at my car - that sounds much lower than anything I've seen.
 

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Wingless Wonder
1988 Esprit Turbo
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5 PSI at idle speed? I gotta look tomorrow at my car - that sounds much lower than anything I've seen.
I agree...I think it is a bit low, too.


a SEARCH pulled up Jonboy's oil pressure topic from a few years ago. Discussion reveals setup of oil pump specs.

 

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Discussion Starter #7
After a bunch more searching I came across an excellent thread over on that ”other” forum last night (low oil pressure reading - intermittent). I actually did read through the post you mention above @carbuff but his problems were quite a bit more involved than what I’m experiencing.

Anyway after reading the other forum post and translating the marks on the pressure gauge based on the posted factory specs I’m much less concerned about the pressures I’m seeing on the gauge. My guess is that I was seeing higher than normal pressures prior to my oil change (sometimes creeping quite close to ”7” on the gauge). I did cut open the old filter and it was quite sludgy and disgusting which may have been the cause of the higher pressures I was seeing prior to the oil and filter change.

Based on the additional reading I’ve done today I think I’m good and appear to be running pressures that are well within factory spec for each RPM range.
 

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1990 Esprit SE
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I’ll drain that new oil and replace with some Valvoline VR1 20W/50
After an extended drive with the oil nice and hot, the pressure can look alarmingly low at idle on these cars.
It's usually slightly higher than your reading but there might be a little gauge error.
I wouldn't be too concerned.
Switching from a 10w60 oil to a 20w50 oil would lower the pressure further at running temperature.
I'd stick with the 10w60.

Andy.
 

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Discussion Starter #9
Switching from a 10w60 oil to a 20w50 oil would lower the pressure further at running temperature.
I'd stick with the 10w60.
Yep I agree @AndyPG. I‘ve also read a few posts on both forums stating that Lotus actually recommends the 10w/60 for our cars now. I know factory original specs are the 20w/50 but maybe they recommend the higher weight oil for high mileage engines. Regardless, I’m sticking with it for now.
 

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Car Adicted
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Maybe 1 bottle of a motor honey type oil would bring the pressure up slightly.. Typically I always wanted 25 to 30 psi at idle and another 10 psi per 1000 of rpm. You can certainly mix viscosity's until something close to that is reached.
 

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Wingless Wonder
1988 Esprit Turbo
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I thought that the 'thickness' (viscosity) (pour point) was a function of the lower number. The higher number is determined by additives that protect when warm.

This is timely:


There is a 275-post Topic on BITOG about the EE video above, too!

 

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Discussion Starter #12 (Edited)
You know @carbuff I’ve been working on cars for most of my life (and I’m approaching the big five oh) and I’ve read and heard so many differing and contradictory explanations on oil numbers that honestly I’ve mostly given up. My most current understanding is that the first number in front of the “W” (which incidentally stands for “winter” and not “weight) indicates max flow at low temps, so the lower the number the better the oil’s cold start performance. Basically the oil stays more viscous at low temps, so a 0W oil has maximum viscosity at cold temps while a 20W is thicker and isn’t as happy in ultra cold temps, especially at startup. Prior to multi-grade oils being developed 50 or so years ago you’d put a lower viscosity oil in your engine in the winter and a higher viscosity oil in your engine in the summer. Multi-grade oils solved that issue allowing you to choose a single oil and stick with it year round.

The second number indicates the oil’s performance at 100 degrees Celsius. The limits are fixed and so any oil that specifies “40” in that second number, for example, must achieve the limits for that specific viscosity. The lower the number the thinner the oil, which is why higher viscosity oils are preferred in older engines since tolerances inevitably increase with engine wear. My ‘53 Studebaker with a blown 400 SBC experiences significant blowby with thinner oils so it gets 60W. On the flip side, when I put 10W/30 in a brand new Mazda 2 a few years ago the dash lit up like a Christmas tree with warning lights. Factory specs for that car were 0W/20. The tolerances on that motor were so tight that the thicker oil was causing issues! As soon as I drained and refilled with the proper viscosity oil the car was happy again.

I bookmarked this one awhile ago and it’s where I got the info above...

 

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The only thing I would find concerning is sudden change. You changed viscosity so that can account for it

I have been chasing an issue in my Excel[N/A but same engine with VDO gauges] where poor grounding and or poor voltage supply cause the gauges to wander with electrical load

When the fans come or you put the headlights on, the temp rises and the oil pressure drops

Just thought I would put that out there
 

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Wingless Wonder
1988 Esprit Turbo
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I’ve read and heard so many differing and contradictory explanations on oil numbers that honestly I’ve mostly given up.
I'm giving up NOW. LOL

IMO, Jason of Engineering Explained did a good job explaining it for the greasy-fingered layman.

EDIT: Sorry for the Topic Drift...

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Discussion Starter #15
The only thing I would find concerning is sudden change. You changed viscosity so that can account for it
It’s certainly possible that I changed viscosities, but since I don’t know what the PO put in it I won’t know for sure. All I know was that the old stuff was seriously nasty and in its current state probably had a viscosity of about 150! 🤣

When the fans come or you put the headlights on, the temp rises and the oil pressure drops
All I can say is ya gotta love British engineering! 😜
 
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Discussion Starter #16

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1984 Turbo Esprit
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I would replace the sender and see what you get. It's old already and tho not leaking, it's an electrickery device that can have failures and one of the symptoms might be low readings. I will be worth the peace of mind.

The oil pump is very finely fitted and can wear causing excess leakage. Next time you have it in for services you can measure it. An easy job to pull and install.
 

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I would stick a mechanical gauge in and see what eh actual pressure is. Could be an instrumentation problem, could be an actual oil pressure problem.
David Teitelbaum
 

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Big end shells may have too much wear. Try to replace them. It can be done from below with engine in-situ. Use ARP bolts.
Also, you may consider adding an oil flow restrictor to the cam towers inserted into the passage in the oil pump housing (brilliant idea of "PellHall" Thomas Pell)
AuxOilRestrictor (PellHall).JPG
IMG_3866.JPG AuxOilRestrictor (PellHall).JPG
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With all the history of posts of concern about oil pressure on the various forums, I wonder why there has not been an effort to provide an oil pump with a longer rotor/annulus set. They're available for VW, Subaru, Chevy et al, but I'm guessing the overall JH/Lotus market is too small.
 
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