Technical Oil pressure PROBLEM with a FIRE...?

[alexGS]

I know that some people (usually new people to the forum) may think that I know everything about Unos, or that I think I know everything about Unos, but neither of these thoughts is true

So with that out of the way, I'd like to know what would be the most likely cause of low oil pressure at idle with the 999cc FIRE engine once it's warmed-up after a 15-minute drive at a reasonable pace. And yes, this is the $120 project Uno, I've neglected to update that thread yet, sorry

Symptom is, oil pressure warning light goes out quickly when engine starts, but once engine is warm (properly warm but not over-exerted), warning light comes back on and stays on with engine at 1000RPM or less.

It's really disturbing to see the light coming on (as you can imagine) - I've been using the choke (just the first part, not the enriching-part) to increase the revs so that the light doesn't come on when I move off from traffic lights etc. since we all know that driving with the light on is going to wreck the engine.

I wasn't so worried about this until today (since the engine runs smoothly and quietly, no knocking.) Then I fitted a brand-new oil pressure sender switch and also changed the oil for a third time (the filter was changed the second time and that made no difference), and this time I put in 20W50 (nice and thick) - and neither of these made any difference! So it's a serious problem

What I'd like to know is, what is the typical cause of this on a FIRE?

On the larger FIAT twin-cams, the oil pump is mounted on the end of the crankshaft and has a thick steel plate on the back (inside the crankcase), held on by countersunk screws. Sometimes these screws work loose and the oil pressure leaks out to the sump. Does this apply to the FIRE?

Some other FIATs have a piston-type valve for the oil pump pressure relief. If this were to stick open, would there still be sufficient pressure to put the light out with the engine cold - and does the FIRE have one of these piston-type relief valves that is likely to stick?

I've heard of stories where some engines lose drive to the oil pump, but I think the FIRE oil pump is mounted on the end of the crankshaft, in the housing that has the filter attached - is this correct?

Finally, do you think that the low oil pressure is the symptom of worn bearings rather than the cause? It seems like a chicken-and-egg situation and I'm feeling out of my depth! Do we have to replace all the bearing shells to cure it?

Thanks for any light you can shed, please. I tried a search but didn't find any case of low oil pressure with a FIRE engine. I'm prepared for a flaming if it has been covered before


-Alex

 

[Chas Uno]

There's only two things I think it could be Alex.

1. Oil pump/ filter blocked and oil pump pressure relief bypass valve is activated. When cold the oil is thick and will register high pressure. As it warms up it gets thinner but is still bypassing oil pressure relief valve. The thinner oil causes the oil pressure to drop due to lower viscosity hence not giving a correct reading via the oil pressure warning light.

2. Main bearings are shagged or other such wear and tear in the engine.


If you have a mechanical type oil pressure gauge you could try and plumb that in place of the oil pressure switch. This would give you a better idea of what exactly is going on. You may find the oil pressure on start up is only just above that needed to extinguish the warning light, or you may find the readings are fine. Either way it would help narrow down the possible causes.

You could also change the oil pump itself. It could be worn/ blocked causing the low pressure.

If the oil pressure is low then there is a risk that the bearings are damaged, though as you pointed out there are no untoward engine noises so fingers crossed they're fine. Then again, you could always pop in a 1242 lump if the worst comes to the worst. Not that difficult (nor expensive) and you'd get a nice little power increase into the bargain

Good luck and look forward to seeing the updates Alex

 

[Uno driver]

I have a little different problem with a FIRE engine. When you start it from cold there is no oil pressure, you can wait on idle for 10 seconds or more but light doesn't come off until you rev it up a little. After reving it up oil pressure light goes off and it doesn't turn on anymore. When engine is warm, it works like new, but when you start it, there is a lot of rattling until oil pressure builds up.

Engine is having pressure problems for a long time - 50.000km or more, but only at start-up. I worry because it's getting worse and worse with every start-up, especially in last few months (maybe because it's winter).

Oil level is on top, oil has 14.000km and it was last changed in summer (Selenia gold). I don't want to put fresh oil in engine until I solve the problem wih oil pressure or replace the engine.

 

[Uno driver]

I replaced oil and filter, but it didn't help at all. It seems to me that all oil from pump, filter etc. gets back into sump over night. When engine is hot there is no problem with oil pressure and engine works like new without any knocking.

I have spare oil pump, should I replace it? Is there any non-return valve in pump that may be broken?

 

[Uno driver]

I think I found a problem :slayer:. Seal at picture is hard and not sealing at all, so when you turn engine off air gets inside and oil leaks out from tubing between pump and sump.

 

[Unoturbo'd]

clean the oil pickup strainer in the sump. sounds as if clogged

 

[Uno driver]

No, it is completly clean, but I was thinking the same thing before I took the sump off.

 

[Unoturbo'd]

well 2 other possible conclusions are that maybe the oil pump is worn, or that the big end bearing shells are worn somehow. not generally a problem for the little fire engine

 

[Uno driver]

Thanks, I have spare oil pump, but I hope it was only the seal. I've just put sump back on, now I'm waiting silicone to dry, then I will start it and see.

When engine is hot there isn't any noticable knocing or rattling and oil pressure is OK at idle (no warning light). I think if there was a problem with pump or bearings it would get worse when engine heats up and oil gets thinner.

 

[Unoturbo'd]

i think ud be best getting the pressure checked by your local garage. it is unusual for a pump of that design to wear. but like anything, you can get problems.

 

[Uno driver]

At first startup light came off after 2 or 3 seconds (no oil in pump). At second startup after sitting several hours light went off immediatly

Problem was because oil pump was rather sucking air through the seal instead of thick oil from the sump.

 

[alexGS]

Problem solved, then?

Which seal? Or was it the countersunk screws loose on the back of the pump? That was the problem on the FIRE I was working on, but we had slightly more oil pressure when cold than when hot.

-Alex

 

[Uno driver]

It was the seal between pickup strainer and oil pump, you can see it here https://www.fiatforum.com/uno/159792-oil-pressure-problem-fire.html?p=1881076

Yes, problem solved, engine runs like new

 

[alexGS]

It was the seal between pickup strainer and oil pump, you can see it here https://www.fiatforum.com/uno/159792-...ml#post1881076

That's in this thread! :doh: Sorry!

I blame my tiny Eee PC screen (and the picture may not have loaded)...
Great to hear it's all fixed.

Update on the original topic: oil pressure problems fixed with the dark-red Uno project, but STILL have oil leak problems from the sump. Sump has been re-sealed four times now, and the oil pump removed, crank seal replaced (jjhepburn even took the engine out to do a really thorough job of cleaning/sealing sump). We've even tried a different sump (it didn't leak at all before). So, I'd love to know how you get on with sealing yours.

-Alex

 

[Uno driver]

I don't know yet if it leaks or not. I cleaned off old sealant and then used alcohol to remove any oil. Then I put silicone on sump, waited for 20 minutes, put it on, wery lightly tightened the screws, waited for another 30 minutes and tightened them as they should be. Then I waited over night for silicone to dry. One hour is not nearly enough (or because it was cold here).

 

[Uno driver]

I did some more testing. Problem is not completly solved, but it's much better than before. When I turn hot engine off (fan kicking in) and then start it again after several hours it takes 3 seconds until warning light disappears at idle. If I turn off cold egine and start it again after some hours, light goes away immediatly.

Is it possible that crank seal has something to do with it? It's leaking, but not badly.

 

[Unoturbo'd]

is there a gasket on the oil pump. not sure if its the same design as the 1301

 

[alexGS]

I did some more testing. Problem is not completly solved, but it's much better than before. When I turn hot engine off (fan kicking in) and then start it again after several hours it takes 3 seconds until warning light disappears at idle. If I turn off cold egine and start it again after some hours, light goes away immediatly.

Is it possible that crank seal has something to do with it? It's leaking, but not badly.

Crankshaft seal won't be anything to do with low-pressure after startup. But, interesting that you're getting a leak there after removing pump - I think we had that too.

Have you checked the countersunk screws that hold the plate on the back of the pump? If they are loose, you get the problem we had (pressure loss when hot).

-Alex

 

[Uno driver]

I didn't remove oil pump, as I thought the only problem was the seal on attached pictue . I will take it off one day in spring, now it's a little too cold for work like this. And as I said, it's much better than before and I'm not worried any more . Before it was critical - light didn't go off at all until I revved engine up at ~1500rpm. Then it went off after ~5-7 seconds.

 

[ralphnz]

Alex, re:sump. Manual, Section 13:18. has a drawing of sump seal fitting. You have probably seen this? But the new seal tapers toward the sump channel, it isn't square as the old seals were, and is to be fitted as illustrated?
Is your seal the wrong way around?