Question about 1995 Mercedes-Benz S-Class

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Overheating 1995 s420 overheating while in trafic. Owner said it started 2 weeks ago. Took a compression test of the cylinders and found 2 each very low (opposing banks). Checked the dou valve and found both plungers corroded in the closed position, with one broken off from the soleniod stem. Removed the plungers and placed the dou valve back into position. Removed and replaced the thermostat. Spark plugs were worn with gaps exceeding .070 and plug wires were heat brittle. Replaced all with new. Started engine and test drove still overheating. Checked the exhaust for water traces along with the oil, none found. Need help, posible head gaskets?

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  • Anonymous May 21, 2009

    This car is rear wheel drive and has one clutch drive fan. It does have twin electric fans for the AC. I did notice the clutch fan doesn't change speed when the engine is hot.

  • Ronald Mueller
    Ronald Mueller May 11, 2010

    is this a front wheel drive/with transverse mounted engine? does it have single or twin cooling fans? doubt it's a head gasket your oil would look milky which you did not mention

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Fairly common problem so i would say it is definitely your head gasket. Sorry.

Posted on May 20, 2009

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Get a piece of cartboard and hold it towards the fan. while is running. if the fan stops the clutch fan it,s bad.I am almost positive that,s your problem.
I hope this will help you out.

Posted on Aug 06, 2009

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2 Answers

Have a spark plug not firing.


Are you sure it's actually a plug?
Are you getting oil on the plug?
The plug may be firing but you may be losing compression which gives the symptoms of a misfire. As you've changed the plug, lead and coil this points to to a problem elsewhere.

Your first course of action should be to get a mobile mechanic carry out a diagnostic check for you.

To put your mind at rest, do a 2nd compression test using a light oil squirted into the bores:

Doing a Compression Test
Warm the engine. Remove all the spark plugs.
Get a pencil and piece of paper to note down the readings.
Put the compression tester into the No1 cylinder and crank the engine for 10 seconds.
Note down the compression reading.
Repeat process for all cylinders.

Here's an illustration of what you may expect on a 4 cylinder engine:
Cylinder 1 2 3 4
psi 125 122 120 124

125 is the uppermost figure for that engine. Here, this engine is fine. There's a slight variation in psi figures, but that's perfectly normal.

Here's the same engine:
Cylinder 1 2 3 4
psi 110 112 114 112

The psi reading is down. However, as all the figures are pretty much equal it doesn't indicate head /gasket problems. It may point towards worn pistons or burnt valves.

Now consider these psi readings:
Cylinder 1 2 3 4
psi 125 84 86 124

There's more than a 10% drop - a difference - between cylinder 1 and 2, and cylinders 3 and 4.
The compression readings for cylinders 2 and 3 is down; low. There's something clearly wrong.

It suggests that there is a defective head gasket between cylinders 2 and 3 or a crack in the cylinder head. The rising piston compresses the gases which escape into the adjoining cylinder via the defective gasket or cracked head.

However, it could also mean that there is a problem with the valves (burnt/not seating properly) or perhaps piston / ring problems.

A burnt valve - it's usually the exhaust valve as they bear the brunt of the combustion - can cause a reduction in engine power simply because the combustion process isn't occurring properly. Compressed air/fuel gets squeezed out of that cylinder because of the damaged valve . There even may be a misfire - a surge as the car runs.

Worn or broken piston rings allow compressed gases to leak past into the crankcase. A compressed crankcase can force oil out of the dipstick tube. The pressure in the crankcase will leak to atmosphere anywhere it can find an outlet.

The 2nd Compression Test
The second compression test is known as a 'wet test'. The first compression test was the dry test because no oil was added to the bores. The second 'wet' test can give an indication of whether it is the rings or valves at fault (though bear in mind rings and valves do not cause overheating or water in the coolant symptoms).

Spray a liberal amount of light penetrating oil into each cylinder - aim for the cylinder walls, not the centre of the piston. You want the oil to run down the cylinder wall and around the piston to form a seal.

Place a rag over each spark plug hole and spin the engine to eject the surplus oil.

Then carry out a full compression test noting down the results.

Here's the previous results with the 2nd compression readings added:
Cylinder 1 2 3 4
psi 125 84 86 124
Wet 128 112 110 126

The readings have increased. This because the oil sprayed into the bores has formed a temporary seal around the piston, thereby enabling the compression to be raised. It also indicates that the bores/rings are worn on cylinder 2 and 3 - the 'oil seal' has increased the readings but is still low in comparison with cylinders 1 and 2.

This could also indicate that in addition to worn rings there is also burnt valves. Oil cannot form a seal around a valve. A worn or split valve will cause a low compression reading and misfiring symptoms.
Compressions readings should be taken in conjunction with other symptoms. It will help you identify the problem:

Low compression readings between two adjoining cylinders point towards a head gasket/head fault if your vehicle has shown signs of coolant loss, coolant in the oil system - mayonnaise, overheating, rough running and lack of power.

If those symptoms are not present it points towards burnt valves/piston rings. A worn engine may be difficult to start and pressurise the crankcase, but it doesn't cause overheating problems.

Feb 09, 2016 | Cars & Trucks

1 Answer

#2 cylinder misfiring why?


Usually if you know which cylinder, you check spark--fuel--compression on that cylinder.
You could do cylinder balance test, engine idling, kill each cylinder, one at a time. If you kill a cylinder that has no effect on rpms, that cylinder is dead for some reason, spark--fuel--compression?
I usually kill spark and do it quickly.

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2 Answers

2002 Chrysler PT Cruiser won't start. Low compression Cylinder 2 and 4


Find an accredited shop that specialises in your vehicle and get on social media to see if there are anyone who uses this shop and how good they are. If you or any of your friends are in a motoring organisation then ask for a recommendation of the shop.. IF you have a V 6 and 2&4 cylinders are adjacent then it will be a head gasket . If not the head may be warped . A competent mechanic will be able you show you where the timing marks are pointing and if the timing is out by the marks not lining up. Forget the replacement engine as it was going and unless the engine was overheating before it stopped then the problem is fixable . IT is just a matter of getting the diagnosis right from a good mechanic.

Feb 22, 2014 | 2002 Chrysler PT Cruiser

2 Answers

Horrible engine knock in 1995 toyota celica


Check for oil pressure.Check the compression in each cylinder.
Yank the valve cover to see if the camshaft is actually turning during cranking mode,only.
Disable the fuel pump or disable the spark(fuel disable preferred)
The engine may have "eaten" something it shouldn't.
A valve may be broken off inside the cylinder head.
Usually an exhaust valve.

Feb 21, 2013 | 1995 Toyota Celica

2 Answers

I have a 99 sienna and the cylinders have low pressure what can i do?


If cylinder compression is too low, the car may not even start because of it. Have a shop do a compression test or a leak-down test to check the internal health of your engine. A good engine should have pressures of 150-200 psi in all cylinders and be close to each other. A worn or high mileage engine may have pressure as low as, say 125 psi, but if still balanced (close readings), would still run decent. Compression below that, especially below 100 psi, is serious trouble. ignition spark refuses to ignite the air/fuel mixture and you get a misfire-a non-working cylinder. Low compression can be caused by worn piiston rings or poor valve sealing. Low compression in 1 or 2 cylinders can be a valve problem, burned valves or valves not seating properly.
A leak-down test will check each cylinder and if there is a problem, the test will find the cause of the problem.

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1 Answer

1995 chevy k1500 4.3 5 speed 150,000 stumbles at idle and while driving slow, and even at higher speed while maintaining my speed it will go erratic and smokes black. Have changed map sensor and ignition...


Did you change the TPS - throttle position sensor . Have you check for vacuum leaks . O2 sensor ? videos on youtube on how to test !
GM OBD Trouble Code 44 4 & 6 cylinders ? head gasket Do a compression test on those two cylinders .

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1997 Jeep Cherokee was an excellent runner until 2 weeks ago. Now it suddenly runs hot and dies. While driving intermittently sputters and miss fires. Check Engine light on. Replaced a few things. Should...


Well the water pump sounds bad....it is a cheap fix at $34.00 and will fix the overheating problem. The O2 sensors start at $63.00...but if you have a "check engine light" on, get it read at the parts store for free and see if the code is for the O2 sensor.

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95 Jeep Cherokee 0 compression in #2 cylinder.


If you have a 0 reading from cylinder 2 that means there is no compression from it and you need an enfine rebuild.It seems that there had been damage to the engine.Have it hooked up to a computer and check diagnostic code.Overheating of an engine can be very costly and damaging, rememeber that always.

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1 Answer

EGR Flow Malfunction, and sometimes a Cylinder 4 Misfire.


How does the oil look? Is it milky or is there any discoloration? Is any moisture or steam vapor coming out of the exhaust pipe? The EGR fault is most likely being triggered from the cylinder missfire. Sounds like you might have a head gasket blown, and/or a cracked or warped cylinder head from the overheating.
You can run a compression test to help determine this.
Good luck...i hope this helps you troubleshoot the problem.

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2 Answers

Loss compression


How to Test Engine CompressionAn engine depends on an equal compression reading in each cylinder to run smoothly. If poor compression exits in one or more cylinders it can cause a rough idle condition and low power. A compression test can be performed to check wear or internal damage. To start a engine compression test gauge is needed. There are two types of gauge styles, one threads into the spark plug hole which is more accurate. The other style of gauge is constructed with a rubber plug that is meant to be pressed against the spark plug hole, this style of gauge is difficult to use. To perform a engine cylinder compression test follow the steps below.
  • Remove ignition coil connector or ignition system fuse to disable power to the ignition system
  • Test ignition system to ensure that the power to the system has been disabled
  • Remove #1 cylinder spark plug and insert compression gauge, most gauges have a hose attachment that is installed into the spark plug hole with the gauge connecting to the gauge hose.
compression_gauge.jpg
Engine Cylinder Compression Gauge
  • After the compression gauge has been inserted, use the starter to crank the engine over for about five seconds. Use about the same five seconds to test the remaining cylinders.
  • Record the compression reading as each cylinder is tested
  • Remove the compression gauge and reinsert the spark plug
  • Follow this procedure until all cylinders have been tested
  • Compare cylinders compression reading, all readings should be within about 5% of each other
If low compression exists a cylinder malfunction exits and further inspection is required. Possible causes for a low compression condition are: burned intake or exhaust valve, broken piston or piston ring, broken valve spring or a blown head gasket.

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