Technical Oil Pressure Light

[MercMeier]

Hi, I have a Bianchina with a 650cc engine. During rebuild I reassembled the front crankshaft assembly improperly and burned out the main and rod bearing due to lack of oil and a bad pressure gauge. I replace the rod bearings and main bearings and crankshaft. The engine has good oil pressure at startup but the oil pressure will eventually drop so that the light comes on after driving for about 30 minutes. I have confirmed that the drop is real by installing a pressure gauge in place of the pressure sensor. It seems like the engine gets extremely hot after running at anything above idle. I don't have any reference Fiat's to compare this temperature to. The thermostat works. No blockages to airflow. Oil pump is working properly.

Any ideas?

Could it be lack of oil getting to the top part of the engine? I'm not sure how much oil should be getting up there if I run with the cap off(I'm not seeing much...)

What sort of engine temps are normal? And how do you measure it?

Thanks,

Dave

 

[JakeF]

Probably the first thing is to check the oil pump. Have to remember that the pump does not actually create pressure. The pressure is created by the engine tolerances as I've understanded. Like a garden hose, if you put your thumb on the hose the pressure rises.
Ofcourse a worn pump will couse problems, but if the engine is "loose" it will have pressure losses.

Keep us informed with this.

 

[kokiksmen]

Probably the first thing is to check the oil pump. Have to remember that the pump does not actually create pressure. The pressure is created by the engine tolerances as I've understanded. Like a garden hose, if you put your thumb on the hose the pressure rises.
Ofcourse a worn pump will couse problems, but if the engine is "loose" it will have pressure losses.

Keep us informed with this.

agree

 

[MercMeier]

Hi, Thanks for the reply!

I have already replaced the oil pump gears and confirmed that it is working by removing the plug just above the pump and turning the engine over.

 

[the hobbler]

Hi Dave;
Sorry to hear of your problems--2 things that I would suggest in light of what you have advised that you have already done:- (1) check the clearance between the oil pump gears and both sides of the housing (I have these at home in an old, pukka, workshop manual) and (2) remove the crank (tedious as this may be) and have all crank journals measured--it may be that in damaging the bearings, the crank journals may have been slightly scored/worn; both these faults will cause low oil pressure as the oil heats up, )and I would suggest, if you are not already doing so, that you use a good quality (Castrol Classic Oils is one) 20-50 engine oil, not one of the modern very thin oils (5-40). Hope all this helps.

 

[MercMeier]

Thanks for the reply!

I am running Castrol 20-50 already. I am planning on pulling the engine and going thru it again. But before I do I would like to try and pinpoint what I am looking for.

The thing that is bugging me is the heat.

It sure seems like the whole engine compartment gets super hot. Wondering if it makes sense that a lack of flow to the top of the engine would cause the (what I think is) excess heat by not allowing the oil to cool as it flows from the top to the sump?

Any tips on how to determine if the engine is running excessively hot or not?

Dave

 

[the hobbler]

Hi Dave;
When you have the engine out and stripped, check that the cooling fan is (a) being driven correctly (ie going round correctly, nut up tight etc), and (b) that there is no damage to the fan--no blade are loose or distorted. On a 500 only 2 things cool it--(1) air being blown across it. by the fan, and (2) air being blown past the sump, which is one reason that when a 500 engine is tuned a larger alluminium sump is fitted (the other reason is that the larger oil capacity gives the sump/oil more cooling capacity)--try this for starter:bang:

 

[MercMeier]

Good point on the fan. I will check that out.

Anyone have any engine temps for me to compare to?

Thanks,

Dave

 

[Bambino]

Dave,
A standard water cooled engine will run at about 80degC (175degF) when at operating temperature. An air cooled 356 Porsche runs at about that temperature as well so I guess that would not be far off the mark for a 500 engine. I'll be installing an oil temperature gauge in my car in the next couple of months if you can wait that long
Regards,
Chris

 

[MercMeier]

I'll see how motivated I am during the cold months here in Minnesota...

Are you going to install the sender in the oil pan? I think I can get my hands on a temp sensor gun that takes a reading just by pointing it at the engine. Not sure what it should read compared to actual oil temp but it should let me know if I'm in the general temp range.

Thanks,

Dave

 

[the hobbler]

Hi Dave;
Had a thought--try laying your hands on a 'stick-on-colour-change' thermometer--this would allow you to easily watch the engine oil temp wothout having to hold/alter anything--much easier

 

[MercMeier]

Good idea!

Just ordered a pack of 3 for about $15.

Factory Effex 08-90225 Temp Specialty Sticker, (Pack of 3) : Amazon.com : Automotive

 

[the hobbler]

Well done Dave;
A pack of 3 thermometers (and I assume you are talking about thermometers--in England something else comes in packs of 3!) will allow you to record engine temperature at 3 different points at the same time--sump, rocker-cover and cooling-air at its outlet by the thermostat would be one suggestion--keep us informed please.

 

[dunnah01]

I've found this very useful for measuring temps around engines:

http://www.ebay.co.uk/itm/Non-Contact-IR-Infrared-Laser-Point-Digital-Thermometer-/360263403953?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item53e15f49b1

 

[jjacob]

If the engine is truly running hot I would check that the fan belt is not slipping causing the fan to run slow. You might also check the fan to see if it is in good shape.

Low oil pressure can be caused by excessive clearance in the main and rod crankshaft journals. You do not have to remove the crankshaft to check this. You can check the clearance by using Plastigauge. These are thin strips of plastic that you put between the bearing shell and the crank/rod journals. You only need to remove one half of the bearing (bottom), put the plasigauge in, reassemble and retorque. Do not move the crankshaft. Then disassemble again and check the width of the Plastigauge. This will tell you the clearance. Check this against the factory tolerances.
John

 

[MercMeier]

Thanks John. I will check out the fan for sure. Also, It's a good idea to Plastigauge again. I've never made an assembly or measurement mistake before but there is always a first time...

 

[MercMeier]

Well, I tested the fan and it is spinning and blowing air just fine. I used an infra-red temperature gun to check temps(the stickers haven't arrived yet and I got impatient...). It got to about 200 F at the valve cover and about 180 at the sump and the oil pressure just kept dropping.

I pulled the sump cover and checked the rod bearings with plastiguage. They were within spec.

I pulled the engine and then removed the crank and crank bearings. The front(timing chain end) crank bearing seems to be the culprit. It is scored and when I put it on the journal it has a lot more play compared to the rear one. The good news is that the crank journal measures to spec.

Not sure what caused this but I have ordered a new bearing and will make sure there is no debris and it has a good coat of assembly lube when I put it back together.

Any other ideas as to why that front bearing is wearing? Could having the belt to the front pulley too tight cause such a mess?

Thanks,

Dave

 

[jjacob]

Did you find any trash in the oil pickup screen? You might want to check the oil pump for scoring or trash as long as you have everything apart.
I don't think a belt that is a little too tight could cause this. My guess is something was in an oil passage or in the oil pump after the rebuild.
I would also check the oil filter slinger assembly and make sure all of those parts are clean.

By the way, I don't think the temperatures you measured are high. Seem normal.
John

 

[the hobbler]

Hi Dave;
I agree entirely with John; the chances of an overtight fan-belt causing the problem are practically nil--if the belt was tight enough to cause a problem with the rear crank-bearing, it would also cause some (small) problem with the front (flywheel end) bearing due to the rigidity of the crankshaft. The cause of the problem, as John says, is more likely to be contamination in the oil passages or from the oil-pump. Whilst you have things stripped down, make sure that the oil-pump is ABSOLUTELY clean as are ALL passage-ways. When you build the engine back-up, may I suggest that you use a 50/50 mixture of STP (or Wynns) with a thin engine oil on ALL moving parts; by using this mix you (a) prevent 'drain-back' which will (b) leave a layer of lubricant on all surfaces prior to starting and (c) effectively prime the oil-pump so that there is no delay in creating engine oil-pressure. Using this build-up lubrication system I have actually pushed a 500 down the road (plugs out, in gear) and put the oil-light out prior to starting the engine! The only proviso to this system is that you do NOT put the unused STP/oil mix into the engine until it is well run-in (otherwise the STP will actually prevent proper running-in of the engine). i hope this helps you and that the problem is sorted--travel well

 

[Bambino]

The only thing I have to add to this excellent advice is that the oil pressure is read from the flywheel end of the crankshaft and if it is low there and you've identified the problem at the timing chain end of the crankshaft, then it will be low along the whole length of the crankshaft thus putting all of the bearings (main and big end) at risk of failure.

As John has said, an oil (sump) temperature of ~80degC (~175degF) is normal. The head will be warmer for various reasons (spark plugs, exhaust gases etc.) and can get quite hot in racing engines - even those that are water cooled.

Keep us informed,
Chris