MadScience_7

I have about 600 miles on a rebuilt S4 (sorta) N/A engine. S5 rotating assembly, TII rotor housings and center plate.

While doing some highway driving yesterday, I noticed that cruising in 5th at 3-3.5k RPM, the oil pressure would slowly drop away to almost nothing if I was on the throttle, but when I let off the throttle the pressure would come back up. No change in RPMs, just the throttle. So while going uphill, I would have to let off the gas every 20-30 seconds to let the pressure build back up for 2 seconds or so. It was a mild grade and it did the same thing on flat ground, though the car would accelerate pretty good so I couldn't test for the same time lengths.

I searched and found a thread from several years ago. The consensus there was pretty much that the oil pressure gauge is crap. I'm not disagreeing with that, but I would like to get everyone's thoughts as to what could link oil pressure to engine load.

Thanks
Andy

jjwalker

Interesting.

I have been sitting here thinking of any relation to throttle opening (electrically, like the TPS) and the oil pressure gauge, and I cannot come up with any possible relationship between the two.

Have you checked your oil lately? The only thing I can think of is that the pump moves a larger volume of oil at higher RPM thus it may be draining your oil pan below the pick up tube. That is the only reasonable explanation I can come up with.

MadScience_7

Actually, this was just after an oil change. I had just put fresh 20-50 oil in and as soon as I noticed the low pressure, I pulled over and checked the level, and if anything it was a little over-full.

I'm starting to wonder if it could be an oil temp problem. Even though multi-weight oils are supposed to get thicker as they heat up, maybe I'm reaching a breakdown point? (god I hope not)

jjwalker

Then I am at a loss. I'd spend the few bucks on some 10w-30 and do a drain/refill and see if that has any effect. Where you running 20w-50 before or did you just suddenly change oil viscosity?

beefhole

iTrader: (29)

Verify for sure with an aftermarket mechanical gauge. Maybe there is some electrical glitch. Either way, don't bother looking at that stock gauge.

importordomestic

go get a manual oil pressure guage from the auto parts store 30$ or so run the line inside the cabin and test again. the mechanical guage will prove beyond a doubt if you are having oil press problems.

MadScience_7

I plan on getting real gauges sometime soon. For now, let's just say that hypothetically I know for sure that the pressure is behaving as I stated before. If so, what could cause that?

jjwalker - same viscosity and brand as before, Castrol GTX 20w-50.

bumpstart

noise cap on the oil pressure sender circuit is probably hanging loose in the bay, put it back on earth with a clean contact

else blow-by maybe effecting the oil circuit somehows
which is why every one is telling you a change of gauge is very prudent

Jet-Lee

iTrader: (1)

My gauge, with the engine off, reads just above 110 lb/in. When running, it's pegged.

Is there a simple reset for this?

Attached is a pic.

jjwalker

That is just a bad sending unit. Get a new oil pressure sensor. The oil pressure sensors resistance goes down with pressure so yours is either shorted, or the wiring between it and the gauge is shorted. Most likely it is the sensor though.

MadScience_7

If by noise cap you mean the little black condenser/capacitor thingy, I replaced that during the rebuild.

So if it isn't a real problem until I can verify it with an accurate gauge, what are some recommendations for gauges? The mazdatrix oil block adapter looks nice, but seems overpriced. Other options for mounting senders?

Jet-Lee

iTrader: (1)

Is this what I'm looking for?
http://www.autozone.com/autozone/cat...&parentId=51-0

arghx

iTrader: (3)

most likely a funky gauge

HAILERS

Perhaps having the wrong dipstick in the engine and or the wrong entry tube for the dipstick in the engine or a combination of the two. In other words...........not enough oil in the pan caused by an incorrect reading on the dip stick.

Check the length of the dipstick entry tube vs the length it's supposed to be on you engine (turbo and non turbo entry tubes are of different lengths and the sticks themselves are of different lengths.

EDIT: Fact is I went back and actually READ your first post (one of my faults is not reading everything) and I'm convinced that with the combination of items that you used to construct this engine, the problem lies in my answer given above i.e. wrong dipstick used with wrong entry tube for the dipstick. NOT ENOUGH OIL IN THE PAN

HAILERS

The pictures I attached in the above thread were from BANZI-RACING and came from this link: https://www.rx7club.com/showthread.p...ipstick+length

jjwalker

Yep.

SirCygnus

iTrader: (1)

happenned to me. you have an oil leak some wheres or your oil needs to be changed.

HAILERS

No. Look at the jpg I attached. The TURBO intermediate housing is on the right, non turbo on the left.

Turbo and non turbo use different lengty dipsticks. The difference in length is the equiv lenght b/t the dipstick ENTRY tube shown in both jpg. If you use the wrong tube/dipstick that CAN result in you not putting in enough oil. When that happens the oil gauge will fall when going up hills and just the opposite downhill. Also during acceleration the oil gauge will FALL for obvious reasons.

What's happening is this. The non turbo dipstick is LONGER than the Turbo stick. You used a TURBO intermediate housing with the SHORT TUBE. So you install the non turbo dipstick and shove it in. The stick will read or show a higher level than what is really in the pan. I suggest you add a quart to a quart and a half more oil then put the right stick in the pan after making sure you have the right entry tube installed on the intermediate housing. Done.

MadScience_7

Actually, this is the second rebuild using the turbo center plate. I noticed the dipstick problem last time and made my own dipstick by cutting the longer one, smashing it flat with a hammer, and stamping marks in it. The oil level should be about even with the top of the pan, correct?

As I mentioned before, this was with fresh oil. I'll keep looking for leaks.

HAILERS

I'll give you measurements of the TUBE and measurements of the dipstick tomorrow sometime in the evening. For a TURBO intermediate housing.

MadScience_7

Thanks.

HAILERS

ON a series four non turbo: the STICK length from the end to where the rubber stopper, stops on the tube, is 14.0" to 14.1" (measured two non turbo stick lengths).

ON a series four non turbo: the TUBE is 3.3" long from it's entry point to where it enters the housing.

On a turbo series four: The STICK is 10.7" to 10.8" long from its end to where the rubber stopper actually stops on the top of the tube.

On a turbo seires four: The TUBE is 2.0" long from the entry point to where it enters the housing.

TUBE length matters. STICK length matters.

I've had this problem. I took a series four non turbo and removed the tube so they could lap the intermediate housing. I made this non turbo engine into a turbo using turbo rotor housings(had brand new ones laying around), and non turbo side housings. After building the engine, I failed to install the tube and wondered why the stick hit bottom of the pan etc. So I yanked a tube out of a perfectly good TURBO engine (stk as can be) and pressed it into the non turbo intermediate housing.

After doing that I often wondered why the oil level gauge acted low going up hills etc. Got smart after a while and noticed the difference in tube lengths and stick lengths. Matched and mated the right parts. Geeeee, my oil level was waaaay low using the right sitck/tube combinations. Added at LEAST two quarts to get up to the proper level. No gauge problems going up and down hills no 'mo.

I know NOTHING about series five stick lengths and tube lengths.

Look at the jpgs on the other posts. NOtice how the TUBE lengths are different and that being so means if you use the wrong STICK, then the oil level will/can be wrong when you check it.

About the stick: I measured from the tip of the sticks bottom to where the rubber stopper HITS the top of the tube. I am NOT measuring from the tip of the stick to where the rubber stoppers bottom end. The bottom end of the rubber is NOT what causes the stick to stop enterning the engine. It's the top of the rubber that stops the stick from entering the tube any more.

HAILERS

Notice the TUBO jpg. Look at the oil FILL TUBE and how where it is pressed into the intermediate housing. Notice how the TOP of the stick tube is level with where the FILL TUBE enters the housing.

Now go look at the non turbo FILL TUBE and where it enters the housing. Now notice how the dipsick tubes top is much higher than the oil FILL TUBEs entry point into the housing.

OIL FILL TUBE is the black tube where you put oil into the engine FYI.

Noticing now the dipstick tubes top is higer in one jpg vs the other jpg makes you realize the has to be two different dipsticks of different lengths.

Then again........the problem could be something completley different

Thank Banzai-RACING for the jpgs.

Rob XX 7

iTrader: (8)

all this talk about the stick length it seems if he rebuilt this motor he would know how much oil he put in when he changed it.

so how much oil did you put in?

And for the record- the stock "shitty" temp and oil gauges, all the gauges actually, read the same as my aftermarket ones and the Wolf, so they aint THAT bad.

beefhole

iTrader: (29)

No, they aren't bad at all. However, the oil gauges do tend to crap out, especially if your forget the resistor/damper thingy. After that, it's probably shot. My oil pressure gauge moves up and down, but is 20PSI off from the mechanical.

The water gauge I trust, it seems acurate. My aftermarket oddly enough doesn't match what my haltech says though.