Oil Pressure For An M180

[230/8]

Here is the issue:

Background: I have a 1969 230 sedan with the M180 engine. It was rebuilt several years ago and has received only seasonal use since then. It is stored through the winter. When starting it in the spring I would always roll it over a minute until the oil pressure raised the gauge and the carbs filled with gas. Then I would pump the gas a few times and, barrooom, it would start every time, no surprises. I use Mobil 1 15w/50 and have for a long time, there are no leaks and it uses absolutely no oil. In all respects, but one, it is a honey of a motor in a classic model. I've owned it 30+ years.

Problem: Two summers ago, when I was starting it up after its winter hibernation I noticed that the oil gauge would not raise when it cranked over, no matter how long I cranked the starter. I did not want to run down the battery so I patted the gas and, barrooom, it started up fine. And the oil pressure gauge moved off the peg like normal. However, ever since then it has done the same thing with the gauge and also, and this is what troubles me, it has a pronounced but very brief bearing rattle for the split second it takes for the oil pressure to build after it starts. This is happening any time it starts from cold. Once the engine is running there is absolutely no noise from the innards, just the good running it has always had. But that cold start rattle really bugs me.

Could it be a worn oil pump and/or oil pressure relief valve? It happened so suddenly...put it away on the fall, just fine; woke it up in the spring and rattle knock. Scares the pants off me. This is a really sweet engine with no other problems. I am reluctant to say that it needs another rebuild with only 12,000 on this one.

Any thoughts?

Thanks,

JCH, aka 230/8

[300SDog]

If hot idle oil pressure is not far below 15lbs and pegs immediately at tapping the gas, then your oil pump is ok.

First place I'd go for checking rattles is valve train. Have you stuck your head in engine compartment while somebody else starts the car?

Btw, if that's the 4cyl 230/8 I've read they are notorious head crackers. Some guy came in here awhile ago from Arizona hollering that he couldnt find a junkyard replacement head for his 230 that was not already cracked same as his. The fellow said he had pulled 3 junkyard cyl heads from "tri-star pete's" famous AZ junkyard.... and ALL of em were cracked!! And yes, i can see where a cracked head would cause valves to start sticking...... a situation that might go away after the engine gets spinning.

Maybe you should be checkin the oil with engine running for telltale signs of water bubbles or check the radiator for oil. I've never cracked a cyl head myself, but these strike me as typical symptoms. Yet the real tell-all would be wet/dry compression test.

This is just one idea, you understand, the rattle could also be something really deadly like piston wrist pin knockin too..... or even just a dislodged rocker arm hold down spring. Whether or not the rattle is related to oil pressure is something we cant easily know..... although head cracking could cause drop in oil pressure too, i think.

Try the search engine here - its excellent and we've got plenty of former and current 115 owners on this board.

[nachi11744]

Hello,
I suspect you have the chain tensioner leaking down. There is a way to *test* it in the factory manual.

M180 is a 6 cylinder 4 main bearing crank engine that was in production in many different specs from about 1951 to 1976 and may still be in production somewhere! It grew into the 2.5 litre M123, made from 1976 till 1985 for the W123 250(not sold in USA). These engines have earned a reputation as bullet-proof machines and were used in cars, light vans, unimogs and probably other applications that I do not know about.

[300SDog]

Then the chain tensioner on early 115's is oil pressure driven.... and leakdown of the mechanism results in robbing oil pressure at cold start to revive the chain tensioner... meanwhile the chain slaps against the tracks causing short-term rattle until the tensioner does its job??

This makes perfect sense to even me who has never owned a Mercedes shop manual. Best regards to Kuala Lumpur Malaysia!!

[230/8]

Thanks for the suggestions. I checked the tensioner last summer and concluded that it seemed to recover quickly after the engine off leak-down and was not likely to be a problem because the starter motor spin-over showed the chain was tight as a size 5AAA shoe and not slapping any visible amount. But, I did not use any "factory method," unless my empirical observation approach just happens to be the factory method. I shall try to rustle up the factory engine manual and will check it again. Any one out there have the CD ROM that would show this? The PDF images can be emailed. I have the chassis manual, but not the engine manual.

Thanks again to all,

230/8

[230/8]

A couple of other related thoughts...the noise is not really a rattle, like that referred to in other posts concerning the newer cars with complicated valve timing systems. This is a solid and deep knocking that occurs for only a split second or two just as the engine starts up cold. The gauge is slightly slow to move for that split second as the oil pressure builds and then immediately runs up to normal pressures, and as the gauge moves off zero the knock leaves never to return, until the next stone-cold start. Also, if the engine starts up with a varooom! and immediately runs up to operating speed the noise is almost non-existent because the oil pressure builds immediately to its full pressure. If, however, it starts up rather lazy, i.e. fails to catch and run strongly, like when it has been sitting for a loooong time, and when it catches it ticks over very slowly at a low speed for a few seconds, then the noise is more prominent.

It is almost like the brief noise one might hear after an oil service job if you fail to fill the oil filter and then must wait that initial short time for it to fill. In all other respects the oil pressure is spot on normal. Very hot days or after a long high speed run it may drop slightly to about 10-15 at idle in gear, but it will immediately peg the gauge at 45 when the engine runs up the gears. Using Mobil 1 15w/50 has greatly helped the hot weather dino-oil thin-out that caused me some concern, but I have never felt that my oil was endangering the motor.

I am just concerned that this change in start-up behavior may be symptomatic of a problem that could grow into a major cost to repair if left unattended. My wife's car, a Mercury, has rattled on for a second or two while the filter fills up after each oil change for ten years now, without apparant adverse affects. Can the M180 engine endure this same type of stress upon start-up without harming anything?

Is it unreasonable to focus on the oil pressure relief valve? It seems that if this valve was leaking slightly and relieving pressure when it should be closed, i.e. at start-up, then the engine might react as it does. Am I off-base here?

Thanks again for all your help.

230/8

[nachi11744]

Hello,
You say deep knocking, like bearing rattle. Then it would seem like a good idea to remove and clean the oil pressure relief valve. IIRC, it is under a cap nut along the driver's side front face of the cylinder block. There is not much that can be done to cure momentary bearing rattle on some engines but it is not common on Mercedes sixes.

At the very least, I would do the following:
1. Clean oil pressure relief valve
2. Test timing chain tensioner for leakdown
3. Remove oil filter housing and clean out relief valve.
3. Check oil cooler thermostat (should be closed at cold start).

You could hook up a master oil pressure gauge at the oil filter head connection to the car's gauge and check how long it takes for pressure build up on cold start. Other than that, I cannot think of anymore tests without getting into the engine to check the main/rod bearing condition.

Hope that helps.

[nachi11744]

Hello,
FWIW, my car's M115 has a sluggish oil gauge as well, from a cold (cool?!! ambient temp 70F minimum here)start it takes it's time to reach 45psi but there are no *unusual* noises as the pressure builds up. Oil is 20w-50.
Have a good week.

[230/8]

Thank you, I shall dig into the areas you have suggested ASAP. I was not aware the oil pressure relief valve could be cleaned, and also unaware there is a valve in the oil filter housing. FYI, my old crock does not have an oil cooler, but does have automatic and AC, which in summer poses a challenge to good running when I use AC on a hot day. Aside from that little nuisance it is in all other respects the perfect old Benz to use everyday; well it would be maybe a little more perfect if it had a hundred extra horsepower.

Thanks again,

230/8

[nachi11744]

Hello,
I guess *cleaning* can only amount to spraying carb cleaner into the block mounted valve, I am not sure if your M180 has a valve in the oil pump as well, some Mercedes engines had both.....please check in a M180 engine manual!

The oil filter has a relief valve to bypass a clogged filter element. Remove the housing from the block and soak in kerosene or diesel overnight, then spray carb cleaner into all the filter head passages.

Very unusual that you car does not have an oil cooler, all 230 W114s that I have seen have oil coolers.

A hundred extra horsepower??????You need to rev up to 5500-6000rpm to see just how quick a 230 is, all straight sixes have a high torque peak, on this M180 it is around 4000rpm. If you tool around at 2000-3000rpm, the engine is hardly breaking a sweat!

Here in the tropics, a car just amounts to an air conditioned room on wheels, so I run a/c all the time, the 2cyl York has long been replaced by a Sanden SD-507 swash plate type compressor, it does slow down the idle by about 150rpm and knocks about 5mph off at 80mph, but at 100F ambient temp, I have 40F a/c vent temp and about 175F engine temp. I do have the 6 blade visco fan from a M130 and a W123 type Bosch electric fan ahead of the condensor.

[kilgor]

This is the wrong thread, but I would like to learn about your A/C conversion...