7040 low oil pressure
Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=170823
Printed Date: 13 Aug 2025 at 1:47pm
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Topic: 7040 low oil pressure
Posted By: nick121
Subject: 7040 low oil pressure
Date Posted: 05 May 2020 at 5:51am
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Have a issue with my 7040, once it's warmed up after pulling wagons or plowing the low oil pressure light will come on at idle, rev it up and it goes out. If it's been plowing for hours and it's really hot it needs to be revved up even more to keep the light off. Let it sit revved up a bit for a while and it will cool down and oil light will go out. I'm thinking I should be getting a mechanical gauge to check the actual pressure? Any ideas what may be going on?
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Replies:
Posted By: wekracer
Date Posted: 05 May 2020 at 6:04am
| Are you talking about engine oil or the hydraulic pressure over 1800 Rpm |
Posted By: Tbone95
Date Posted: 05 May 2020 at 7:16am
| Sounds to me like the sensor and light is working perfectly. |
Posted By: DrAllis
Date Posted: 05 May 2020 at 7:23am
| Engine oil pressure should be minimum of 35 psi at full throttle and max of 55 psi. HOT idle pressure probably 15 psi on a sound engine. GET A GAUGE AND CHECK IT. |
Posted By: MACK
Date Posted: 05 May 2020 at 7:54am
| How many hours are on bearings? MACK |
Posted By: Tbone95
Date Posted: 05 May 2020 at 9:06am
| Well, we still don't know if it's engine oil or hydraulic over 1800 he's talking about, do we??? When I originally read it, I thought engine, but wekracer asked the right question. |
Posted By: nick121
Date Posted: 05 May 2020 at 9:29am
| Sorry, engine oil is the issue. |
Posted By: Tbone95
Date Posted: 05 May 2020 at 9:31am
| Well then yeah, you either have a funky light, or an actual problem. As regular as it behaves, does certain things when hot, hotter, engine rev, etc., to me it sounds like you have an actual oil pressure problem and the light is telling you that. An actual gauge will give you a number you can compare to what Doc stated. |
Posted By: ACjack
Date Posted: 05 May 2020 at 9:44am
| If I remember correctly in order for an engine to pass test it had to have a minimum of 10 psi hot at low idle. |
Posted By: DrAllis
Date Posted: 05 May 2020 at 10:07am
| It is very possible the oil pressure sender is bad, causing the flickering light issue. The Customer needs to connect a gauge and verify the oil pressure when hot and at different engine speeds. Anything else is speculation. |
Posted By: nick121
Date Posted: 05 May 2020 at 7:43pm
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Seems like it's a real issue here, the light does follow the temperature of the oil to close to be electrical I think, if it was electrical I'd think it would be more random. I can screw a gauge into where the oil pressure light switch is? Try and get agauge somewhere this week, bit harder getting things with shops closed down. Would you know what size thread it is? Looking in my service book, it has a section on cleaning the oil pressure regulator valve?could be stuck open , would that be a possibility or not likely?
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Posted By: DSeries4
Date Posted: 05 May 2020 at 8:10pm
The light does not follow oil temperature, it measures oil pressure. Usually if the sending unit is bad, the light will not light up at all - even when turning the key on before start up. ------------- '49 G, '54 WD45, '55 CA, '56 WD45D, '57 WD45, '58 D14, '59 D14, '60 D14, '61 D15D, '66 D15II, '66 D21II, '67 D17IV, '67 D17IVD, '67 190XTD, '73 620, '76 185, '77 175, '84 8030, '85 6080 |
nick121 wrote:Posted By: DougG
Date Posted: 05 May 2020 at 8:22pm
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Had to been engine oil |
Posted By: nick121
Date Posted: 05 May 2020 at 8:48pm
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I know it doesn't follow temperature, I'm just implying as the oil gets hot it's thinner/ drops pressure. which the light indicates, let it idle for a while after it's been worked and the light will eventually go out. But as Dr said at this point it's all speculation till I get a gauge on it to verify whats happening. Was looking for possible suggestions on what it could be If I do in fact have bad pressure
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Posted By: nick121
Date Posted: 05 May 2020 at 8:49pm
| Not sure on hours on the bearings, only owned the tractor since 2018 and hr meter doesn't work. |
Posted By: MACK
Date Posted: 05 May 2020 at 9:57pm
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I would put a T in so you can monitor gauge and light at same time. The fitting is 1/8 pipe thread. A grease gun hose works good. If I was guessing, I would say worn bearings, oil pressure line loose from pump to block. The 301s blow gasket in pump, but had that on a 426. MACK |
Posted By: SteveM C/IL
Date Posted: 05 May 2020 at 10:22pm
| with unknown hrs and care it likely could stand brgs...if not too far gone already |
Posted By: AC7060IL
Date Posted: 06 May 2020 at 10:01am
| Nick121, I’ve been following your post. Hope it’s a minor solution & not an expensive one. What engine oil viscosity & engine oil filters are currently in use on your 7040? You say that you’ve owned it for 2 years(2018 buy). Any chance you could please share any previous owner’s use/service/maintenance/intervals records or considerations? |
Posted By: FREEDGUY
Date Posted: 06 May 2020 at 6:34pm
To the "gurus" of this issue, would/could an oil additive (STP OIL/Marvel), help Nicks light problem if indeed it's pressure related (granted, short term)?? Seems like our WD, D17-15 and 19 had a gauge that at least had a needle that pointed to a letter in the word NORMAL in the gauge, why did ALLIS go to an idiot light in the 100 series and newer ? To Nick, hope you get it figured out, have a safe planting season 
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Posted By: nick121
Date Posted: 06 May 2020 at 8:30pm
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It had fleetguard filters and I assume 15w40 just before I bought it he changed it. I recently changed it out with agco oil 15w40 and agco filters. I only put limited hrs on it in a year maybe 100 hrs part time farming a few acres thats a good distance from home, so haven't checked anything on it yet until Saturday. And the previous owner hardly used the tractor, bought it sitting used it a bit and sold it to me in 2018, haven't had any issues until march this year hauling corn out of the field. I have a 7045 and 7050 just purchased recently as well, so maybe take the oil pressure switch off one of those and try it on the 7040. Thanks Freedguy, You as well!
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Posted By: DanWi
Date Posted: 06 May 2020 at 10:05pm
| I don't know if they are the same but on my 190xt the side of the motor the pipe that feeds the turbo oil pressure has an elbow that has a plug same size as oil pressure gauge that you can screw a gauge into I used a couple of elbows so I could see the gauge from the seat. |
Posted By: Lonn
Date Posted: 07 May 2020 at 7:16am
------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |
Posted By: SteveM C/IL
Date Posted: 07 May 2020 at 8:34am
| HEY!! QUIT DIKN AROUND AND PUT A GAGE ON IT !!!!!!!! |
Posted By: nick121
Date Posted: 15 May 2020 at 4:26pm
| So I found the connection for the oil pressure switch was quite corroded and cleaned it up and also tractor wouldn't start, battery cable was loose. Fixed that and cleaned up connection and light is not coming on any more. Just when you start the tractor for the first few seconds and after it's shut off and pressure declines. I'm going to get a gauge yet and put it on when I get a chance. |