Is there a way for me to tell if I have a cracked engine block or is it a head gasket job I need on my 1991 300 SE

Symptoms: When the car is at a red light the temp guage goes up. When the light changes to green and I accelerate, the temp gauge goes back down. I was told about 3 years ago by a Mercedes Dealer that I needed a head gasket. This is a "second car" to me, I don't drive it that much. The problem has stayed the same, it does not appear to have gotten any worse or better over all this time. I am a bit hesitant to believe the dealer because I also have a Mazda and oddly enough around the same time a Mazda Dealer told me that my Mazda needed a head gasket and I have found out that was not true.

My 3000 SE is really starting to go through coolant. I normally only drive it once a week and that is just around the block but I find that I need to put coolant in the overflow every week. When I moved the car today I could tell that the coolant was leaking from further back and not by the front of the car. When I took the car in to the Mercedes dealer 3 years ago they also told me I needed a radiator and a water pump.

My concern about a cracked engine block is this. About 3 months ago I had taken the car around the block and I did not know it, but the overflow was bone dry and the car heated up and went into the hot. I shut it down right away. Since then, it has continued to do what it has always done. It runs ok until I am at a stop light then heats up but once I accelerate the temp gauge goes back down.

If I cracked my engine block - would the car even run?

It sounds to me that you may need a new water pump. If you had a cracked block you would find coolent in the engine oil and oil floating in the overflow tank for the radiator. Have you checked the belt. Check the color of your oil. How old are the hoses?

92 300E 139,000
77 Datsun 280 2+2 68,000
02 Dodge Quad 4 By 4
04 Expedition 4 by 4 38,000
00 Mustang 6 198,000
05 Mustang G.T. 23,000
89 Jeep Pick up 198,000

I don't know how old the hoses are, I did have a major tune up done on it about 2 1/2 years ago. I needed to replace the distributor cap and it had been awhile since I had a tune up so I did that, as well as a transmission service and got all new plugs.

I do keep an eye on the oil and it looks pretty clean to me. And I really don't seem to loose oil. It's about half way between full and low.

As far as I can tell, I can't see any oil in the overflow tank. What I do see is the coolant level going down.

I had a transmission guy driving my Miata several months ago and I was describing the symptoms of my Benz to him and he said it sounded like a water pump. This was before I drove it that one time without there being any coolant in it. I did take the cap off the overflow when it was really hot, but it was empty. I don't think anything happened, because nothing came out.

Which belt should I check? I'm not afraid to go looking around under my hood.

One other thing I have noticed under there is the long black cover over the plugs seems to be loose or it won't shut down all the way. I don't know what the deal with that is but I guess it does not affect the driveability of the car.

As stated above, with either a cracked block or blown head gasket there would be high probability of water in the oil or oil in the water.

Double check the cooling system. Have you tried filling the cooling system, idling the car in the driveway and you under the hood/car looking for a water leak? If the water exits the overflow tank, then the cooling system is at fault.

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1983 500SL Euro

I never thought of doing that but I will try it. (I'm female and I know nothing about cars).

To me, what does appear to be true is that a mazda dealer told me my miata needed a head gasket, which ended up not being the case. And a mercedes dealer has told me that my benz needs a head gasket which from the sounds of it, may not be the case either.

It seems to me that you can't trust dealers and all they want is your money.

Thanks everyone for your advice. I wish I would have found this site months ago, it would have saved me a few headaches.

Hi,
Park you car on a hill so that the front of the car is higher than the back. Remove the cap on the overflow cap and add water/antifreeze. When the engine comes up to temp check to see if the water/antifreeze in the tank goes down. If it does keep adding until you have a quarter full in the tank. If you see air bubbles coming out that would be great. Check around the water pump and hoses and the radiator for leaks. Check the wheel on the water pump and make sure it is working right,not wobbling.

If you want to ensure that you do not have a cracked block ( doesn,t sound as if you do) ensure the over flow is at a good level and let the engine set over night. If you do have a cracked block you will see a flim of oil in the overfow tank. There could be many more reasons for this problem but at least its a start.

Thanks for the tip. I might try that. What I really need to do is get the car into the mechanic I use that I trust and have him do a block test. I've been putting off doing that because the dealer said I needed a head gasket and a valve job and he gave me a price of $3,500. This was 2 years ago so I am sure they would charge me more now.

After reading the replies here it really does not sound like I need a head gasket. I don't have any oil floating around in the overflow tank and my engine oil is clean. I've been told if water was in there there would be a white color mixed in with the oil. Nothing like that is on my dip stick. I've been looking for a Mercedes board for awhile. I found a Miata board last year and discussed my problem with the guys on there and they said that the Mazda dealer was full of crap. It appers that the Mercedes dealer might be full of the same thing! I think some of these dealers know that a lot of women don't know a thing about their car. Which in my case, is true.

Let's get back to simple basics.

Check your viscous fan clutch.

Verify that the aux cooling fans (electric fans in front of the condenser/radiator, right behind the grill) turn on as the temp rises at a red light.

When the weather is warm, it is normal for the temp to rise when the car is stopped in traffic, especially with the AC on. As the temp rises the aux fans will turn on at high speed and cool it down, and the viscous fan clutch should engage the engine-driven fan. You can hear that fan make a sort of roaring noise as it moves the air through the radiator when you accelerate.

The coolant loss is not normal but based on what you've reported, to assume it is the head gasket is premature. It could simply be a hose. A cracked block is not likely.

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2012 E350
2006 Callaway SC560

Thanks for your response.

Boy, this is starting to sound a lot like the Miata board. The Mazda dealer had my Miata for 20 whole minutes and swore up and down I needed a head gasket. The guys on the Miata board said that those cars hardly ever need a head gasket and how did I run my car so hot that I needed one? Answer was - I didn't.

Based on all the replies here and also on what the transmission guy who worked on my other car said, I think my Mercedes needs a water pump. Oddly enough, that is one of the things the Mercedes dealer said I needed! A Water Pump, A Radiator and a Head Gasket.

Thanks again everyone.

PS Brewtoo - I live in Los Angeles and the temp gauge does the same thing no matter what time of day or time of year. If it is hot, or if it is raining. If I sit at a red light for more than say 5-10 seconds it goes from around 80 degrees up to the 100 mark and sometimes a little over that. As soon as I accelerate, it goes back down to the 80 degrees. Of course this whole head gasket thing has freaked me out a little and now I hardly ever drive the car. I put about 4,000 miles on it last year and I live in LA!

It sounds as if you know more than you think! At least when it comes to people feeding you a bunch of B.S. If the car had a cracked block or bad head gasket two years ago you have known it by now. Your problem doesn,t sound that bad, at least for a car with that much age. Please let us know how it comes out.

J.D.
Charlottesville, V.A.

Just curious, why a water pump? They are usually replaced on these cars because they leak (but they don't tend to leak as much coolant as you say you are losing and you said your leak is more toward the rear of the engine). Loss of pumping capacity is not likely.

Besides the coolant loss, everything you have reported is within the realm of normal.

Have a look at those heater hoses above the engine in the back on the driver's side. I saw one of those with a pinhole in it once and the coolant loss was significant.

This may very well turn out to be a simple problem.

You are asking wise questions. Listening to the dealer can be like asking a barber if you need a haircut!

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2012 E350
2006 Callaway SC560

I will. I am planning on having it towed into my mechanic in a week or so. I have to get a smog by July so I need to get whatever is wrong with it fixed.

I have done some homework. The Miata board I found was a bunch of guys who rip Miata's apart then rebuild them as race cars. So they did give me some of the ins and outs of things. But I took that as pertaining to a Miata, not a Mercedes. My Miata had entirely different symptoms than the Benz does. And the head gasket that the Mazda dealer diagnosed turned out to really be a sticky thermostat! $30. part and my mechanic installed it for free!

From my experiences:

Loss of coolant:
- Cracked coolant tank
- Hose going bad (in my case, the heater hose burst a few weeks ago on my W124...also in the shop for the head gasket btw.

Water pump failure:
- Weeping coolant leak near pump at first, complete purge of coolant on garage floor upon total failure.

Head Gasket:
- Worsening oil leak, actually BAD oil leak. Temps climb significantly while stopped, even in cold weather. Depending on engine, oil and coolant mix is also a symptom.

Cracked engine block:
- Oil/coolant loss, mix of both in coolant tank. Noiser engine. I find this to be a rare issue.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

thanks again brewtoo. It does leak toward the back of the engine, I could tell when I moved it today. There was a bunch around the front of the car, but when I moved it I could tell by the trail of coolant that it stated at the back and went to the front (I was parked on a slight incline).

Something else I do notice when I put coolant in the overflow, if I look down at where the oil pan or whatever is there at the bottom of the engine, I can see a bunch of coolant laying there. Which makes me wonder how safe it is to even drive it around the block - is that stuff flamable?

I'm going to print all this stuff and take it into my mechanic when I tow it in. I did that from the stuff on the Miata board and it was helpful.

G-benz - I really don't have any oil leaks, or at least not anything major. I do keep an eye on it. I've only had to add oil to it once in the last 3 years and that was probably a year and a half ago and right now the dip stick is half way between full and empty.

I can't swear that I don't see any oil in the overflow, but it sure does not look like it. I just see the coolant level going down. But I don't drive the car enough. Just around the block once or twice 1 time a week. Maybe I should do it more than that then check it out? But the engine does not make any noises, and my mechanic said if I cracked my engine block he would think it would be making some kind of noise. Like a pinging sound or a clanging sound. A knocking type sound. I don't hear any noise like that.

By the coolant level going down. Last Sunday I filled it to the full level, and today it was probably 3/4 of that. And from last Sunday to today, all it did was sit (except for the drive around the block). When I moved my car is when I saw the trail of coolant from the back part of the engine (I would say the mid point of the car maybe), to the front of the car.