Another Oil Pressure Issue

[markw 1]

Chaps,

I am having some strange oil pressure issues with my XU9J4RS engined sprint car, I get the following

readings on my stack oil pressure gauge (electrical not mechanical and a new sender)

cold 35psi

hot 15psi

when you rev it the pressure rises to 60-70psi

its an XU10 oil pump and an uprated oil pump spring and has never done anything like it before,

under heavy braking the stop light flickers and the gauge drops to nearly zero, but as soon as you get back on the load pedal the pressure picks up again?? even with a baffled sump and windage tray set up any ideas,

could a sludged breather pipe cause these symptoms?

thanks

Mark

 

 

 

[rallyeash 155]

For reference my dry sump system monitored by my full Stack dash is as follows

 

70psi cold idle

30psi hot idle

60-70psi 4-6k rpm

 

It does drop to 15 psi idle when parking up in the paddock after a 15 minute track session

 

Although if I don't like it I can just adjust my oil pressure on the pump

[jackherer 543]

Have you definitely got enough oil in the sump? When you say XU9J4RS you mean a GTI6 head on a 1.9 Mi16 block? Is the dipstick and tube all correct and giving an accurate reading?

[rallyeash 155]

Good point. When I build a 9RS engine the dipstick wouldn't read correct so I measured it in and made a notch on the dipstick to where it needed to be.

[2052NV 24]

I also get a warning flash under braking, I have a deep tin sump (just under 8l in the sump alone), extended pick up, custom trap door baffles, 2.7L accusump and a high pressure spring in the pump. I think its simply oil surging to the front of the engine under extreme braking. Mine did it more so when you were coming out of a bend then getting into braking straight away (i.e. oil going to one side then the front) I figure this would only be fixed by going dry sump? As my car is just a fun club track day car i just "drive around the issue" And try not to be as mega on the braking in the spots where i know it happens.

[2052NV 24]

And its not oil level for me as if i top it up above where im filling it too, i get it blowing into my catch tank staight away. thats how i found out where the max mark was any way

[markw 1]

Jackherer

Yes you are right, it's an mi block with a gti6

Head, the dipstick tube and sump are std

Mi16 parts, and the oil level according to the

Dipstick is 3/4 full.

Why should I of modified the dipstick??

[jackherer 543]

It just seemed like a possibility that the dipstick/sump/block combination might give an erroneous reading when you build a hybrid engine, I don't have any specific info that would lead me to that conclusion. However I've seen exactly the same surge under braking on standard Mi16s when the plastic top on the dipstick has broken and let the stick go to far down the tube giving a false high reading.

 

Do you recall how much oil it took to get it to 3/4 on the dipstick?

 

You could try topping it up to the max. mark and see if that improves it.

[markw 1]

Time up for an update, I bought a oil pressure test gauge and from cold got the following readings

 

52psi idle 0 mins

60psi 4.5k (2 mins)

26psi idle (8 mins) water temp 55 degC

23psi idle (13 mins) water temp 75 degC

55 psi 4.5k

15 psi idle (16 mins) water 90 degC and oil 65 degC

50 psi 4.5k water 90 degC and oil at 65degC

 

Does this seem "normal" for pressure to drop off so much as it warms through,

or is it worth me taking the sump off to have a look??

Obviously I couldn't replicate the heavy braking in the garage to get the stop light on

 

thanks

 

Mark

[welshpug 1,657]

that does seem a little low, my gti6 engine shows 6 bar cold idle pressure and 2 with the oil on 90, goes up to 6 bar with a rev when hot.

[markw 1]

Thanks WP,

Looks like the sump will be coming off then.

[markw 1]

Right I have drained the oil and measured what has come out of the sump, bearing in mind the dipstick showed just under full, and I haven't removed the filter or drained the 13 row mocal cooler

only 3.5l came out of the sump, does this sound right, according to the Haynes an mi16 oil capacity

is 5.3l, I also checked the oil pump for RTV silicone "bits" but I cant see any

 

Do you think I should refit the sump, change the filter and fill with 5L of fresh oil and see where it comes to on the dipstick?

 

I could take the pump off but I don't really know what I should be looking for.

 

Thanks again

 

Mark

[welshpug 1,657]

Are you not using the original dipstick tube and dipstick for the block and sump?

 

Capacity for most XU engines with a steel sump is 5.0 litres, the 0.3 is probably for the oil heat exchanger and lines, so you wont always get the full 5.3 to drain out, but still a good 4.5-5 should drain.

 

I would be inclined to pop a few caps off an inspect the bearings if you have had several instances of low pressure warning.

[jackherer 543]

It sounds like you need at least 1-1.5 litres more, and IIRC the difference between the min and max marks on the dipstick is only 0.7 litres.