head gasket symptoms

[67fintail230s]

Hi,
I have a 1975 230.4. Yesterday, on the highway, I noticed the temp gauge was spiked. It happened 25 miles into a 200 mile road trip. The air temperature was a beautiful 85 degrees F. We pulled the car off the highway. The radiator cap relief valve was clicking as the gas evacuated through the overflow. There was no indication of a leak. My first assumption was a failed waterpump which would cause the uncirculated fluid to overheat and boil over. Once the car was cool enough to add water (~3/4 of a gallon), a restart confirmed the water pump was not seized and was operating with no unusual sound.
My new theory is that the head gasket failed between a cylinder and a water jacket. The cylinder pushes air into the system. This causes superheated air pockets. These bubbles expand the fluid and eventually make it to the radiator cap and make the overflow look like a green volcano. I managed to drive the car back home with the temp gauge hovering at about 190 (normally 170) and the heat at full blast.

If any one supports or disagrees with this theory or has any suggestions before I order the gasket kit, I would really appreciate any input.

Thanks

Anthony

[300SDog]

Bought my first MB - a 1965 220Sb with an already blown headgasket, one of several easily repaired bargain Benz's that I've owned. The engine ran like crap with a couple of low compression cylinders, naturally. Coolant showed up as bubbles on the dipstick. And even worse, alot of coolant poured out the oil drain plug when changing the oil - making me think the car was driven with bad head gasket for awhile. After simple DIY repair, the car ran well and lasted through 4 yrs of college.

If you are thinking blown head gasket caused overheating to occur, thats an interesting theory whereas overheating is known to blow gaskets and warp the head. Maybe *cracked* cylinder head is root source of the problem. Either way, its a bread and butter operation to pull the head. But have heard that decent 230/4cyl heads on the used parts market are becoming scarce.

Hey, does anybody know when MB went from cast iron to alloy heads on their 4 cylinder cars? Am thinking my '63 190c had cast iron head.

[mzsmbs]

first, I'd check oil for coolant, and cold coolant for oil-if you really think that's the head gasket (bubbles in oil or grayish oil, oily slime in the coolant)

second, I'd check the upper hose to the rad (squeeze-use gloves) when engine is HOT! and see if you have flow there-eliminating the pump

third, I'd check the thermostat to see if it's stuck one way or the other.


....before I'd dig @ the head....

[280S]

I never experienced overheating with my car (280S, M130 engine), which had a blown head gasket. The first symptom was that the coolant needed more frequent refills and that sudden burst of vapor and coolant came out of the radiator cap and the side hose. I had to check the coolant level every morning in order to avoid overheating. Also, starting the car in the morning became difficult.
I hope this helps.

[Mark DiSilvestro]

One way to know if there's a severely failed head or gasket, is if the radiator builds pressure rapidly while the engine's still cold. See if the radiator hose gets hard or tries to 'balloon' after running for less than a minute. Often, if an engine with a bad head or gasket is driven, much white smoke will come from the exhaust while running or after restarting. Less severe head or gasket leaks might require a CO detector at an open radiator cap.

I concur with 240DieselDog's theory about overheating being most likely cause of failed head or gasket, though, on these aluminum heads, neglect of coolant changes can damage heads and gaskets too. You possibly could have had a thermostat failure, and I once had a '72 220 that used to run fine for weeks, then AFTER returning from a monthly 400 mile, weekend trip, it would overheat on the way to work the next morning. Fortunately, I would spot the temp guage and pull over before any damage occured. Refilling the radiator would 'cure' the problem until my next trip.
Turned out the waterpump had an intermittent seal leak that only happened after returning from those long trips and the engine had cooled off overnight.

By the way, the 4 cyl OHC 190 gas engines had aluminum heads from their introduction in 1955. The diesels continued with cast iron heads until the early '80s 190 cars.

Happy Motoring, Mark

[67fintail230s]

Here is what I have checked so far:

There is no oil in the coolant and no coolant in the oil.
I let it run for 1 minute, shut it off, opened the cap, and there was no pressure in the cooling system.
The pH of the coolant is between 9 and 10.

I have never had a thermostat stick closed but I would rather replace it then the head gasket.

I may try a leakdown test first. I have never done one. If I hook up the pressure gauge in the spark hole, turn over the engine until TDC for that cylinder, note any pressure drop and put my ear to the open radiator and listen for bubbles? Would that work?

thanks

Anthony

[Mark DiSilvestro]

A pressure guage or a compressed air hose?
The usuall way to check for coolant leaks is with a hand pumped radiator pressure tester.
Thermostat sticking (either open or closed) is how they usually fail. If you're not leaking coolant and/or getting lots of white 'smoke' from the exhaust, I'd check the thermostat first.

Happy Motoring, Mark

[Benzcrusher]

Many of my old benzes were project cars before I parted them out. Several of them had blown head gaskets which had been replaced by a local indy shop. I am confident that failure to retorque the head bolts after a few hundred miles killed these engines.
Well, one engine had the WRONG head gasket, the PO paid $1100 in 1992 for that favor....

Moral of the story, buy the FSM for your beast so that you and or your mechanic will know how to proberly do head jobs!

Another note:
If you do a head job make sure your crank bearings are in top condition, otherwise you'll spin bearings under the "extra" load of a tight top end. Many engines will allow you to remove one or two bearing caps from the lower oil pan opening.....

[67fintail230s]

found the thermostat at my local parts store for $13. That is the plan for tonight.

thanks for the input, I'll keep you updated

[67fintail230s]

Here's the skinny on the recent coolant boilover.
I decided to remove the thermostat to verify a sticking thermostat. I found since the thermostat supports the O-ring it couldn't stay out. So I replaced the old thermostat and went for a test drive. Drove about 30-45 min in city and even parked it and left it idle for 15 minutes. Temperature remained stable (around 180). Drove home on the highway ~15 miles at an average speed of 80mph. Temp remained stable. Parked it at home with no signs of overheating. Temporary blockage? Temporary thermostat sticking?
I do love those repairs that fix themselves.