Oil Pressure dropping Toyota 1HZ

Submitted: Monday, Mar 01, 2010 at 23:46
ThreadID: 76470 Views:7160 Replies:7 FollowUps:8
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G'day,
I have a 94 Troop Carrier with a 1HZ. Its has done 415,000k's. I have done about 40,000 in it. Recently the oil pressure gauge keeps going up and down, today it was hanging around the lower central mark on the gauge at 2500rpm's, at lower revs it would pick up. I regularly change the oil & filter, around every 5000, last 2 changes I've used Castrol 15W 40 diesel oil. The temperature is consistently in the middle, never moves. Does anyone have any ideas why the pressure may be dropping?
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Reply By: dbish - Tuesday, Mar 02, 2010 at 00:05

Tuesday, Mar 02, 2010 at 00:05
First thing Id be suspicious of by your description is the oil pressure sender they do wear out & give erratic signal to the gauge. Daryl
AnswerID: 406803

Reply By: Member - Old Girl (QLD) - Tuesday, Mar 02, 2010 at 00:06

Tuesday, Mar 02, 2010 at 00:06
We put two new senders in and still wont work even took the dash out and had it recalibrated. That's after a rebuild in the TD 80 when cold sits on first Q then drops as you drive along. Apparently nothing wrong with engine mech checked the pressure, its done over 30000k like it.
Jumping the fence soon if it keeps giving me the HMM.
AnswerID: 406804

Reply By: Member - ross m (WA) - Tuesday, Mar 02, 2010 at 00:22

Tuesday, Mar 02, 2010 at 00:22
Yours sounds like a gauge or sender problem.
If the pressure goes sky high when cold and fades away to nothing when warmed,it maybe from worn main bearings

The best and only way is to beg,borrow or steal a mechanics pressure gauge and plug it into the hole where the sender is.
From memory ,the 1HZ should be able to hold 36 psi at 2500 rpms for 2 minutes when warmed up.
50 psi+ is more like normal

AnswerID: 406806

Follow Up By: furph - Tuesday, Mar 02, 2010 at 08:09

Tuesday, Mar 02, 2010 at 08:09
The book says more than 29kPa (4.5psi) idling, more than 245kPa (35psi) @ 3000rpm. Engine at operating temp.
The gauge does seem to vary somewhat, I just put it down to the mood its in.
Checked the actual pressure once (mine) and it was idling at 12psi, 35psi @ 2000rpm.
furph
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FollowupID: 676615

Reply By: Enormous Racing - Tuesday, Mar 02, 2010 at 00:23

Tuesday, Mar 02, 2010 at 00:23
Thought it might be something like the sender, I'm going to look into changing it, any tips on changing one? or cost. I had to drive 3 hours today in Perth, it was 39 degrees, so I was slightly pooing myself so to speak.
AnswerID: 406807

Follow Up By: howesy - Tuesday, Mar 02, 2010 at 02:24

Tuesday, Mar 02, 2010 at 02:24
try these, dont know what toyota charge

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=400104805009&ssPageName=STRK:MEWAX:VRI
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FollowupID: 676597

Follow Up By: guzzi - Tuesday, Mar 02, 2010 at 10:03

Tuesday, Mar 02, 2010 at 10:03
Its an electric gauge on a high mileage vehicle.
Clean ALL the earths in the engine bay and under the dash you can find.
Start at the Battery neg terminal and work from there.
Clean the earth on the engine block.
If this makes no improvement change the sender.

Cheers
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FollowupID: 676639

Follow Up By: Rossco td105 - Tuesday, Mar 02, 2010 at 10:23

Tuesday, Mar 02, 2010 at 10:23
Hey there,

Had exact same random fluctuations on guage as you recently. After advice changed the sender (easy job to do) and all 100% again. Got a Toyota one and the plug was different for some reason, got the auto electrician who looks after the car to get one and his was quite a bit cheaper (apparently a good quiality japanese replacement-Sakei or something). Can let you know the company if you require.

Cheers.
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FollowupID: 676641

Follow Up By: Member - ross m (WA) - Sunday, Mar 07, 2010 at 21:50

Sunday, Mar 07, 2010 at 21:50
4WD Parts in Welshpool, Odin Auto Parts Balcatta,A1 Auto parts Myaree sell the sender for about $30.
Its a common part used on about 40 toyotas made in the 80s and 90s,petrol or diesel.
Mine had Camry written on it.
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FollowupID: 677638

Follow Up By: Member - ross m (WA) - Sunday, Mar 07, 2010 at 21:51

Sunday, Mar 07, 2010 at 21:51
I was advused not to use he $7 one from Thailand;)
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FollowupID: 677640

Reply By: Member - Ian H (NSW) - Tuesday, Mar 02, 2010 at 11:47

Tuesday, Mar 02, 2010 at 11:47
I would give the engine a dose of CEM to clean out all the crud from so many K's. It may even take two doses if the oil is BLACK. It will surprise you how much comes out. Then check the sender unit with the oil clean. Good luck with it.
AnswerID: 406852

Follow Up By: Member - Ian H (NSW) - Tuesday, Mar 02, 2010 at 12:00

Tuesday, Mar 02, 2010 at 12:00
Sory, I should have said CEM is an oil flush teatment.
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FollowupID: 676657

Reply By: Enormous Racing - Tuesday, Mar 02, 2010 at 22:37

Tuesday, Mar 02, 2010 at 22:37
Thanks everyone, all good info, will give it a go. Since changing the oil & filter every 5000 I have noticed the oil staying cleaner, longer. I am using Castrol GTX Diesel 15 W 40 by the way & Ryco filter.
AnswerID: 406981

Reply By: Enormous Racing - Sunday, Mar 07, 2010 at 17:38

Sunday, Mar 07, 2010 at 17:38
Thanks again, I replaced the oil pressure sender unit with an after market one from Repco, cost $18. The new one doesn't have an earth terminal so I dodgily used a hose clamp on the outside of it with a bit of wire and a spade terminal. The guage doesn't even work semi properly, the needle jumps straight to the top then slowly creeps down to the bottom. Does anyone know how much resistance I should get at idle?
AnswerID: 407681

Follow Up By: Member - Wayne B (NSW) - Sunday, Mar 07, 2010 at 20:48

Sunday, Mar 07, 2010 at 20:48
The Sender unit has ti be compatible with the gauge. If the calibration is incorrect you will get readings all over the place.
Sounds like the incorrect sender unit
Cheers
Wayne
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FollowupID: 677627

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