Problem diagnosed!

[Morris]

Since I rebuilt my motor (and added an oil pressure gauge) I have been frustrated by low pressure. Most specifically, low oil pressure at idle after a long highway cruise. Well, I finally bought me a cheapo infrared thermometer from Habor Junk. Checked the temp at my oil filter after cruising around town. Oil pressure at idle 20 psi, oil temp 185°. Perfect. Go for a highway cruise and pull over for a check. Oil pressure at idle 11 psi... youch! oil temp 207°... YOUCH!!!

Just ordered a new oil cooler kit from Summit Racing with my Santa money. Huzzay!

I can't tell you how many hours and dollars I spent trying to figure this stupid problem out. I thought from the beginning it was an oil cooling issue, but I continually second guessed myself. Doh! I am both smarter AND dumber than I think.

 

[JPSmit]

Doh! I am both smarter AND dumber than I think.

at least you're that - I'm only half and it's not the good half if you know what I mean

congrats

 

[Trevor Jessie]

Refresh my memory... did you rebuild this engine? If so, what did you have done?

 

[Hap Waldrop]

207 oil temps are not anything too bizare, but you will benefit from a cooler. 9 times out of ten too little of oil pressure results from too much clearnce at the rod beearing, either too much with a fresh engine, or bearing wear on a older engine. Two questions to start with.

1. Did you resize your connecting rods in the rebuild?

2. What was your final rod bearing clearence?

 

[Morris]

I did not resize my rods. My final bearing clearances where in the .002 to .003 range.

I realize things could be worse than 207°. But I am getting 207° under fairly easy driving conditions. If I can keep my oil pressure where I want by keeping my oil around 185°, which the cooler *should* help me achieve, I will be happy.

 

[Trevor Jessie]

I'm going to guess that you may end up treating symptoms and never cure the problem. I'm thinking like Hap, that there is an issue with the bearing clearance.

 

[Morris]

 

[aeronca65t]

Morris:

One of things I did on my 1500 was to make sure the oil pump side plate was flat. The pump impellers wear into the side plate and create a worn "trench" which can reduce oil pump efficiency.

It's not a difficult job. Just get a nice flat piece of glass and put a piece of fine emory paper on it and "sand" the plate until it's flat. You can even do while drinking beer! :laugh:

I do not run an oil cooler in my race car. Oil pressure is good (25 psi at idle), even after a four hour enduro with average rpms at about 5500. My rod bearing clearances are similar to your's.

<span style="font-style: italic">Note to others reading this: We are discussing a 1500 Spridget where the oil pump is in the pan (not like the A-series where it's behind the flywheel).</span>

 

[Morris]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]One of things I did on my 1500 was to make sure the oil pump side plate was flat.[/QUOTE]

Thanks, Nial. You suggested this in an earlier topic I started on this subject. And I did it... and it did seem to bring up my oil pressure a couple psi.

I have checked, rechecked and checked again my bearing clearances. They are within spec. The only place they may be out of spec is on my cam. The 1500 cam has no bearings, and I reused my old cam when I rebuilt. The next time I have a pocket full of cash and a lot of free time, I will replace my came with one from an early Spit. This will allow me to install cam bearings.

While I agree that oil temps are not the actual source of the problem, addressing that symptom will keep my car alive and healthy until the source of the problem can be addressed. When you have a high fever, you take aspirin to bring it down even though the aspirin does nothing to the virus that is causing the fever. Same principle applies here.

As for the oil temps themselves, consider the following: optimal oil temperature for a car under normal street use is 185-195. I was measuring 207° at the filter under very normal (not hard) street driving. It is quite possible that the actual oil temp in the motor is a bit higher then 207° as the filter itself acts as a kind of heat exchanger. Regardless, 207° is too high for highway cruising on a cool night.

I believe the high oil temps are related to increased combustion temperatures caused by running an aggressive spark curve, increased compression, removal of my EGR and a relatively lean mixture (at highway cruise I run a mixture in the range of 15:1 to 14.5:1. It used to run at about 12:1 on my worn out ZS150 carb). Anyway, the oil cooler should be insurance against bearing failure while I continue to experiment with my fuel injection/spark control system in pursuit of finding the *perfect* settings for power, cleanliness and economy.

 

[Sarastro]

If you have a problem with oil pressure, there can only be a couple of causes:

1. Pump isn't putting out enough oil;

2. Bearings and such aren't providing enough resistance to the flow (i.e., clearances are too great);

3. Oil viscosity, which we all know is a function of temperature, isn't great enough.

It seems to me that you are assuming that the problem is #3, but the temperature you measured doesn't seem to be far enough away from the norm to cause a dramatic drop in pressure. Of course, the oil in the engine is probably hotter than what you measure at the oil filter, but not hugely.

Once I replaced an oil pump in a car (not an LBC), which just wasn't pumping efficiently. I took it apart and measured all the clearances. It looked OK, and for the life of me, I couldn't see what the problem was. But I replaced it, and it fixed the problem. So, while less likely, this happens.

In the end, it's hard not to conclude that there is a bearing clearance problem somewhere. Probably the main or rod bearings, as Hap says, but conceivably it could be anywhere that the oil should meet resistance; for example, camshaft or rocker bearing surfaces--if the oil gets through some gap too easily, pressure will drop. But I'll be interested to hear if the oil cooler solves the problem.

By the way, are you sure the gauge is correct?

 

[JPSmit]

what viscosity oil are you using?

 

[Morris]

20-50

 

[Gray_Cat]

Oil pressure relief valve fresh?
Roy

 

[Sarastro]

If you have pressure when it's cold, some pressure when running and hot, but it drops to nearly nothing at idle and hot, that's probably not going to be the relief valve. I've seen very little difference in oil pressure between 20W-50 and 10W-30 for some reason; seems there should be a noticeable difference, but I didn't see it on my car.

Oil pressure can get pretty low in a hot engine at idle; mine is only about 10 PSI and, from what I've heard, that's not unusual. The rule of thumb is 10 PSI per 1000 RPM when hot. Get the oil a little hotter, have a gauge that's a little off, and suddenly you don't see oil pressure. That's why I asked if you're sure the gauge is OK.

Back in the 1960s, the oil pressure in my TR4A ran a little lower than the specified value. I started putting STP into the thing, which raised the pressure, but I'm not sure it really improved the lubrication. It raises the pressure by making the oil thicker, so it's more difficult to force it through the bearing. Is that an improvement? Maybe, if it stays in the gap between the bearing and journal better, but I'm not sure. Cheap fix, though.

 

[Hap Waldrop]

I did not resize my rods. My final bearing clearances where in the .002 to .003 range.

That could be your problem, thats too uch for a street engine. Let me tell you a story about rod bearing clearence on the A-series engines that will shed some light on this, and maybe help you. Since I started doing this Spridget racing stuff, years ago, I always was told by the Spridget race engine building legends, .002" was the was the bestnumber to be used for rod clearences. A few years ago, I was contracted by a couple of guys to build them a race prepped 1275 bottom end, they suppiled me with thier specs, the only thing out of the norma was they requested .0025" rod clearence, I questioned them on tis, and they said that is what they wanted. Now this guy had netted tow SCCA championships, so who was I to question them right, so .0025" it was. I was building myslef a new 1275 race engine at the same time, ad decided I would use this same recipe. WEll the engine ran fine, but for the first time in my career I was fighting oil pressure problems, I end up over regulating the crap out out of the prssure regulator to get cold pressure up, that helped a bit, but not as much as I waned. I was always use to 80+ Psi cold and 70 psi hot after a 18 lap national race, with this motor I was lucky to be 60 psi cold, and 40-50 psi hot at the end of the race. While everything ran alright and the motor was fast, if you let the engine go anywhere near a idle coming into to impound the pressure would drop to near nothing, that made me fell uncomfortable. When I quit racing SCCA, Iended up selling the motor to friend of mine, and decided to repalce the crank and size everyhting back to .002", well guess what the oil pressure wnet right back to the 80 cold and 70 hot like I was used to, tuen out my buddies in Texas ended up having the sameissues I did with the .0025, and when they heard what I had done went back to a .002" set up and saw the same improvements I had.

Here's the deal, as little as.0005-.001" too uch clearence on the rod in a A-series engine can let too much oil bleed off the at the rods, and make the engine struggle harder to mantain oil pressure. NOw in our case we got the extra clearence at the cranshaft journal, so our fix required new cranks, but yor problem is more than likely waer to the housing bore (big end) of the connecting rods. Bottom line I will not build a engine without sizing the rods, you may get lucky, but the odds are you will not. What I see sizing A-series rods as with most connecting rods, that over time they will grow at the parting line, and this will increase clearence, as well as not securely hold the bearing. Resizing rod is relatively cheap, so do ing it along with replacing rod bolts I feel are a necessity when rebuilding one of these engines, it the key to having good oil pressure in my opinion. In race engine you always have mre clearence than you would in a street engine, I buil my street A-series motor on rods and main at .0015".

 

[Hap Waldrop]

Just to elborate more on this, think about how the oil get t the crank, the oil gallies feed the main bearing and then the crank feed oil drillings feed the rod form the mains, and then the oil blleds off the rods form the side clearences, so the rods are the last in line, if the clearence is too big, the blees off will hppen too quickly causning the engine to not mantian decnet oil pressure. Too much side rod clearence can pay intthis as well, I often heard .014" said to be the near perfect rod side clearence, but I saw engine that had great oil pressure with side clearneces as little as .008" and as much as .020", you can of course adjust too tight of rod clearence by facing the thrust area of the rod, this is most commonly done on a blet sander, but there is not much you can do if you have too much other than swap components around, most of the time you see too much or too little rod side clearence this happen when a set of rods and crank that were not a match set form the factory is paried together.

Also, here's a little tip on replacing rod bolts in 1275 rods, the factory used nylocks as a nut, kinda a joke if you ask me, anyway if you go to buy new replacment rods bolts for your 1275 from british parts vendor, you see they are quite expensive for what is a very questionable fastner choice to beging with, it turns out that replacing with ARP rod bolts (part # 206-6001) is more affordable than using new replacment factory style rold bot set which was a joke to begin with, so use the ARP rod bolt set, you save money and get a real set of fastners.

 

[Morris]

Update: Oil cooler is installed. Oil temp is down 10-12° (195° F) and oil pressure is running 15-17 psi at 900rpm idle after a long trip down the highway.

Currently the oil cooler is right against the radiator, so my oil temp seems to be dictated by my water temp. I am currently running a 195° thermostat, so when I put my summer thermostat in (it's 175°) we'll see if that drops the oil temp a bit more.