I have 10psi when warm and about 10 miles on engine. I would like to have more oil pressure as I figure it will only get worse in time. I have 10w30 oil in the car.

I also have a leaking rear seal. The engine has been modified some, not sure what is in it, it has roller rockers and is supposes to make 400hp.

Would the low pressure be an indication of a need for a high volume oil pump? Or something else?


Second question the engine is running around 200deg. I figure this is fine for now but during the summer in Houston traffic it might be an issue. The radiator is old and leaks so it needs to be replaced. I know the aluminum radiators are 27% better than stock but are the heavy duty ones at an auto parts store similarly better if I don’t care about weight? My wife is on a fairly tight budget at present so cheaper is better unless I end up needing the more expensive one later.

Last question the car will not start or even turn over when hot. I have tried a heat shield and same issue. I am thinking I need a high torque starter. Assuming it is a starter what is the simplest way to determine the compression ratio? If it is too complicated I will just get a starter to cover me. A mechanic who installed the exhaust thought it sounded like 12 or 13 to 1 but that was just by sound of the engine.

 

There are many schools of thought on HV oil pumps- 10PSI warm and 10 miles on the engine, I'd wonder about the guy that built it- almost sounds like way to much clearance in the rod and main bearings, or an internal leak.

Not real uncommin for an engine to run a little warm with no more miles than you have on it. Check the accuracy of your gauge too.

I'm running 12.5 compression on my BB and a stock starter with no problem- check the ground between the right motor mount stand and the block- it may be bad/disconnected/missing. And the ground from the battery to the frame. turn on the headlights and then turn the key to "start" and see what the lights do.
Maybe someone else will jump in on the compression- they only thing I can think of there is knowing what pistons are in it along with combustion chamber size, along with the usual bore and stroke.

 

Is the oil pressure sender and gauge OK? What was the pressure before the rebuild?

If there's nothing mechanical wrong perhaps thicker oil would up the pressure enough - try 10W-40, 15W-50 or 20W-50 instead of the 10W-30.

 

As an experiment, try putting 10W-50 or 20W-50 motor oil in at the next change and see if it increases pressure at all. If it does, and the oil pressure [when engine warm] is satisfactory, keep that grade of oil in the car. If it increases it some, but not enough, you should try a heavier pressure relief spring in the pump. A street-built SBC engine rarely needs a hi-volume oil pump to get adequate lubrication. As far as the radiator goes, your best option [considering needs and cost] is to have your radiator 're-cored' by a competent radiator shop. If you can't find a good auto rad shop near you, look for one that works on truck radiators. They won't gouge you because it's in a Corvette (actually, you don't want to tell any rad shop the unit is out of a Corvette because they will likely jack-up the price), and the work is just the same, as long as they can get an appropriate sized core. If the integrity of the rad tanks and fittings are good, the unit will be as good as new when you get it re-cored, it will cost significantly less than a new aluminum radiator....and it will still be an exact fit in your car! A new alum rad in your car would be nice....it just sounds like it would be out of your desired price range.

 

I will change to heavier oil when I replace the rear seal. If that does not work I will start looking in to the engine, the mechanic sucked.

The radiator in the car is shot, case leaking, core leaking, a used one the mechanic sold my wife(not at the time). I am debating between spending $250 on the heavy-duty one from the auto parts store or $500 for the Al one.

I will check the wires as that is simplest but I found a lot of posts on heat soak issues and the minni starters fixing the issue that sound a lot like my issues. When the car won’t start I open the hood wait 5 minutes and it starts just fine. I was hoping you could some how use a compression gage and calculate the compression ratio.

I know with go-karts we use to put oil in the cylinder at tdc than again at bdc and calculate the ratio but you can’t tip a car engine upside down to get the oil out.

 

Would you even be able to run it on pump gas if it was 12-1 or 13-1?
I've never heard of being able to tell the compression ration by listening to the exhaust, that sounds like BS to me.
My stock L-48 ran at 200 till I replaced the fan clutch, it now runs at 180.
On a previous car I had the hot starting issue and it turn out to be bad wiring connection to the starter.
BTW, lots of books out there that tell you that 10 psi/1000rpm is sufficient oil pressure
Good luck.

 

'79 has electric op & temp gages & sending units. The Finn asked if gage/sender ok.

Suggest first thing is just go buy a new op sending unit & replace it; probably $15 or less at local parts house.

Me thinks you might do same with your water temp sending unit.

If you're smart enough to wrangle a gokart motor around to figure comp ... me thinks you're probably smart enough to install a universal fit race alum rad (<$200).

*everything on the internet's suspect; including the very words I just wrote.

 

What is the oil presure off idle? If it is low maybe you have a problem, but if it is 40+ leave it alone. On your cooling 200 is not bad but it will probaly come down some as the engine gets a bit looser. The correct rad. in good condition and clean and all will be just fine, you would only need the other types if you had other problems or a lot of power above stock.

 

I would think a heavier grade oil would help but if your running a high volume/pressure pump it should be atleast @30psi at 1000rpm and go passed 50 psi when revved up.
In most bad cases it's the pressure relief valve in the oil pump(cheap fix) or as said before excessive clearance somewhere.(expensive/this sucks fix)

 

Per Smokey Yunick, 10psi (warm) for every 1000rpm you turn is all you'll ever need, and that doesn't mean 60 at idle if you are going to rev to 6000, rather 60 by the time you get to 6000. Very much more than 10/1000 will cost power, increase wear, put additional heat in the oil, and open your filter's bypass excessively, so IMCO one should not consider overly high pressure "insurance".


TSW

 

While I agree with the "Smokey Rule" I also usually see 20psi at idle on any well build Chevy motor with proper clearances.

 

Ok never up the oil weight to make up for low psi

Check your gauges to verify they work correctly

I agree on the 10 psi per 1000rpm

Sounds like a fresh motor and you are using a leaky radiator

Dewitts aluminum, or at least a non leaky, unblocked clean one

Did you use a new thermostat? What temp is it?

Mini starter might fix your problem on hot start, but check your timing to see what its at too it will make a diference if your dizzy is locked out on full timming

12 or 13 to 1 compression hope you are running race gas or premium with some good octane boost!!

Who built your motor or where did it come from?

There are ways to figure out your compression ratio you just need to know the numbers but to know that you need to know the exacts on your motor from your builder or where you got it from. Example bore size, piston in the hole from deck, piston profile, gasket thickness, head chamber size + or - mods and cut down on heads.

 

From what I've seen it's typical to have a bit more than the 10/1000 at low RPM's.

What gets me is the all to common thought process that if some is good, more is better. Guys, SBC's and BBC's just don't need huge pressures to be "safe".

 

My suggestion was to put a heavier oil in as a TEST. If the more viscous oil raises pressure (when engine is warm), then there is not some missing or omitted orifice/plug that the owner needs to be worried about. If it does NOT, the owner needs to look further and find the source of the problem. I was not suggesting that he/she stay with that grade of oil....unless they choose to.

 

As a lot of you already know. I lost oil pressure due to my own ignorance. Luckily I think I caught it in time. The motor is running fine now but I still have low OP. After about 15 minutes of run time this afternoon The electric guage in the car registered 10 psi constant @ 950 rpm idle. The mechanical guage under the hood was 20 PSI. Both guages are "T" off of the block port above the oil filter. I am running Royal Purple 10w30., The OP does shoot up when the motor is reved. I would definately like to see a little more pressure at idle.

I did replace the electric OP sending unit this evening to make sure it was reading correctly. However I have not cranked it to see if that made a difference yet.

 

10 - 20 PSI (warm) really isn't low OP at an idle of 950. What matters is do you have at least 20 by 2000, 30 by 3000, 40 by 4000 and so on. You simply don't need anything near 50 (warm) at idle or 75 at 3000 to overcome the centrifugal force at the mains and adequately supply everything else...

 

20 PSI at idle warm with 10W-30 is not bad. I think 10W-40 is fine for these engines in most applications. 10W-30 is for newer engines. They are designed with tighter clearances. Synthetic will generally show lower pressure.

 

Oil Pressure: I'd be interested in how the oil pressure acts under driving conditions. If it drops to zero then comes back up as you come to a stop, or if it drops when you hit the accelerator before then increasing, check the clearances on a couple main bearings. You have to pull the pan anyway to replace the rear seal.

If the pressure goes up nicely and smoothly as you accelerate, reaching at least 30 psi during normal driving (i.e 45-55 mph), you're good to go. That said, I personally prefer a high pressure pump and have run one in both my Corvettes. Just makes me feel better knowing I have 60-70 PSI at 6500 RPM.

Water Temperature: Texas is hot. I lived in Houston when I rebuilt my current small block. After the rebuild, while I could keep it at 200 degrees on a normal day driving on a hot day it would go to 230 degrees at a stop light. Same fan, shroud, etc. I bit the bullet and installed a BeCool aluminum radiator. Same fan, same shroud. (This is a 74 so it's all mechanical.) I never go above 180 any more. Best decision I made - just expensive.

 

Thanks for the info. I guess I have always been in the camp of "More is better". But I guess that is not necessarily true. My OP does grow with engine rpm. I will need to verify and document exact readings at each rpm for future reference. I am now running 10w30 RP Synthetic for the first time and it does appear to have lowered my OP from the 5w30 Valvoline VR I was running.

Wade

 

1st statement here wont help you but the second statement is absolutely true.

Spring pressure behind the bypass valve determines when it will open. If it is designed to open at 60 psi, it doesnt have any effect on anything below 60 psi - UNLESS IT STICKS OPEN - if it sticks open pressure will be low at idle and then build up to the 60 psi at which point the valve would normally open.

I personally wouldnt be comfortable with 10 psi at idle either and there have been good tips for you to try to determine what you need to do.

1. check your pressure with a mechanical gauge - the electric senders are notorious sometimes and keep in mind its something that previous owners rarely change, yours may be original.
2. look at how your pressure reacts under driving. If the engine has excessive clearances in anything but the rod bearings oil pressure will be uniformly low throughout the rpm range (compared to good clearances). If rod bearings have excessive clearance oil pressure will be low at idle and could get worse as rpm rises before going back up.
3. while 200 deg wouldnt worry me much where I live, given where you live you definitly want to get that fixed. A replacement radiator from a local shop should work fine if you are on a budget. but you must make sure that you are using a fan shroud and have all the gaskets around the radiator and shroud that you are supposed to have. If you are not running the factory clutch fan then either install one or go to electric - dont use a fixed flex blade fan. You can also run a higher pressure cap.
4. I doubt very much you are running even close to 11:1 CR as you pointed out judging compression by the sound of the exhaust isnt exactly the same as having measured it. In any case for a small block to make 400 hp (assuming it actually makes that - claims from builders/sellers are often inflated) you dont need anything near that kind of CR.
5. Your starting issue sounds like heat soak - does the solenoid even click when you turn the key? Get your engine temps down and this likely goes away, otherwise a heavy duty solenoid, or a mini starter are all possible solutions.
6. fix the rear seal, leaky vettes arent much fun

Did you purchase the motor? or did the seller claim to have replaced the motor prior to your purchase? in any case 10 psi at idle with 10 miles on the motor is reason enough for me to go back to the builder, similarly the rear main seal shouldnt be leaking with so few miles unless the seal wasnt installed properly, I know of no break-in period for the lip seals used in the small block, they either work or they dont.

I have no doubt in Smokeys reccomendation its been used for many years as a rule of thumb, but it seems to me that Ive never seen a factory car straight from the factory with 10 psi at idle, Ive never owned a GM car that had that kind of OP from the factory. I dont have an owners manual but I would be interested to know what it may say about OP. I would want at least 20 psi @ idle when hot