The Stovebolt Site Forums The Shop Area Engine Shop How can I tell if exhaust leak is due to cracked head or blown head gasket?

I took my 52 chevy 1/2 ton with a 216 to a mechanic because I couldn't figure out why it suddenly started running hot (200 F). He did the test for exhaust gases in the coolant and said the blue stuff turned about as yellow as it gets. I'm considering removing the head myself. How do I tell if the problem is caused by the head gasket or a cracked head?

You can't until you pull the head & examine it. The offending cyl. will usually be cleaner then the rest.

you got any water coming out of the tail pipe

I removed the head without any problems, thanks to the instructions in the manual. The machine shop said they didn't find any cracks in the head and it was not warped. The only problem they found was that the valves were not seating very well (they did some sort of pressure test). I'm afraid to ask, but what other way could the exhaust gases be getting into the coolant?

Are there any "leak lines" in the head gasket? That would indicate a head gasket leak as being a possible culprit.

A crack in the block would cause your leak. I hope it is your head gasket. Did you see any difference in the appearance of the combustion chambers (like one being really clean)? I know that this was already asked, but it is very telling for a head gasket leak.
Carl

Here are some photos of the block I took right after I removed the head. To my untrained eye, all the cylinders look about the same. I also didn't notice any "clean" combustion chambers on the block (sorry no picture). The shop said they found some gunk in the head that looked like StopLeak stuff. I'm not sure how that would have gotten in there. When I had the engine rebuilt about four years ago, the block and head were cleaned in a chemical vat. At that time I took the radiator to a radiator shop to have it cleaned and checked for leaks. Recently when it started overheating, I took the radiator back to the same shop to have it checked again.

Someone had asked earlier if I had water coming out of the tailpipe. I did not see any.


https://www.dropbox.com/s/s0gpdfw03wvalo7/IMG_0262.jpg
https://www.dropbox.com/s/7vh1x5tg2wj8psy/IMG_0263.jpg
https://www.dropbox.com/s/cmxo76prpwj20s9/IMG_0264.jpg
https://www.dropbox.com/s/evib62h11hn4apq/IMG_0265.jpg

You mention that you had it rebuilt, what did they do? Did they install hardened valve seats? It looks to me like you have had coolant in it. Maybe tiny cracks in head, if the seats were replaced they could be causing a leak if not properly installed. I would ask them more about how they pressure tested it.

Hardened valve seats were installed when I had a valve job a few years before I had the rest of the engine rebuilt. So that would have been about 8 years ago. The overheating started in the last 6 months. I will ask them for more details on their pressure test.

Hi Billydon, most likely is you had the head gasket loosen up and was pushing the compression into the water jackets, before you took the head off you should have checked the torque of the head bolts to see if they were at the proper torque#. there is 100 lbs. or more of compression in the cyl.and in the water there is only 13 or so of pressure. so if the head loosened up you will push compression into the water, that will turn the fluid yellow for sure, not having signs of water into the cyl, chambers, and the machine shop says the head is not cracked and is flat is a good thing, clean everything up and install new gasket and try again if you don't find any cracks, its hard to see in your pictures if there was a gasket problem. you didn't have any water dripping from the tale pipe and 200 degs. is really not that hot and maybe your thermostat stuck, did it boil over out of the radiator? if not put it back together , replace the thermostat.

The only thing that stands out to me is the #4 / #5 exhaust port in one of your pictures. It doesn't look like the others, white and dry, yet the pistons are equally colored. Water / coolant usually "steam cleans" the tops of the pistons. Could be it wasn't run long enough to get a good cleaning.

If it were mine, I would install new gasket and go again, flush out the old coolant and run water for a while just to flush out remaining gunk. The stop leak could have been added when you had the truck back at the shop for checking. With out being there or knowing the shop first hand, its hard to tell what they did.

Joe

It never boiled over, but the gauge was getting pretty close to the top end. It was pushing coolant out the overflow even though the radiator was only filled to slightly over the fins. I had already installed a new 160 degree thermostat (but I checked and both the old and new thermostat were opening up at around the right temperature).

I picked up the head from the machine shop today. They said the head must have gotten over 240 degrees at some point because the little indicator that was stuck on the side of the head (by the guy who rebuilt my engine I guess) had melted. They said none of the combustion chambers looked any cleaner than the others. When they checked for warpage they couldn't get a 3000th feeler gauge between the head and their straight edge, so it shouldn't have any trouble sealing with the head gasket. They also showed me how they did the pressure test. They seal off an intake or exhaust port with a piece of rubber that has an air hose and gauge attached. They said it should read around 18 psi, but mine were reading from 11 to 15 psi. I told them the engine wasn't missing or lacking power so I was just going to put everything back together with new gaskets and hope for the best. They recommended using some sort of copper-based spray on gasket sealer from Permatex on the head gasket, so I stopped at the NAPA store and bought a can. I have ordered a valve job gasket set from Jim Carter. Once I put everything back together I will flush out the cooling system and run it with water for a while as Joe H suggested. I will let everyone know how this turns out.
Thanks to everyone for all the feedback.

I think that I would have another machine shop look at the head. Sure sounds like a crack in a combustion chamber to me. The copper coat for the head gasket is only used on some types of head gasket. If you are using a modern FelPro gasket no spray is required. The heat tabs are a tattle tale devise used by engine builders and some machine shops use them. When an engine gets to hot it melts the center out of the tab.

Possible the temperature gauge is wrong???

That test checks for valve seat sealing, NOT cracks into the cooling system. Find a machine shop that can do a pressure test of the cooling passages, and/or a magnaflux test where the head is magnetized and an indicator powder is sprayed over the surface to find hairline cracks. So far, nothing definite has been done to detect any cooling system/compression leakage. If you put it back together now, chances are the problem will still be there.
Jerry

Fel-Pro makes some good gaskets. Their instructions will tell you if they need a sealer. The Fel-Pro Permatorque's don't. Stay away from CORTECO (DETROIT GASKET). They have had some real junk in their sales line.

Copper coat is a sticky glue like spray with fine copper pieces mixed in. The idea behind it is the small copper bits work there way in to the small pits and machining marks to seal off the small leaks. It works really well. It sure won't hurt to use it, but with a good paper faced gasket like the Fel-pro's, you shouldn't need it.

Just how long have you been driving the truck before it got hot? years, months, days?

I have seen guys wipe oil across the whole head surface including the chambers and let is set for awhile. Then go back with brake-cleaner and wipe it off. You could see the oil creep back out of the cracks once the surface was clean.

Joe

The machine shop did do a magna flux test and did not find anything.

I've had the truck since 2003 with no overheating problems. In 2007 I had the engine rebuilt. Until last fall the temp gauge had only gone past the 180 mark on very hot days and even then not much higher. Now even on cool days (60 degrees) after about 15 minutes the needle starts climbing past 180 and eventually will be close to the high end of the gauge.

Did they install hardened valve seats in the head?

It sounds like you've got radiator trouble, not something internal with the engine. Once the heat goes into the coolant the radiator has to get rid of it. Sediment deposits in the radiator tubes can interfere with the coolant/air heat exchange and the coolant goes back into the engine too hot. Do an aggressive chemical flush or replace the radiator.
Jerry

Yes, they did install hardened valve seats when the valve job was done when I got the truck back in 2003. I've put about 30,000 miles on it since then.

Hotrod,
Would radiator trouble explain why my coolant tested positive for exhaust gases?

No, if it was showing exhaust in the coolant, there has to be a combustion-to-coolant mix happening somewhere. That can be a crack, a blown head gasket, or a combination of both. If the overheating situation was chronic, it's possible the gasket could have developed a leak after several incidents of too-hot operation. I'd strongly reccomend a good radiator and water jacket cleanout as part of your reassembly routine. One quick check for exhaust gas or compression pressure in the cooling system is to crank up the engine with the fan belt removed and water or coolant poured into the engine level with the base of the thermostat housing, then goose the throttle a few times before enough heat develops to boil the coolant. Any big bubbles or gushing of coolant indicates a compression pressure leak into the cooling system.
Jerry

The reason I ask about the valve seats is I've seen guys bore to deep when installing them and ending up with coolant leaks. If it were my truck I would pull the valve out and look things over before installing it again. It may be ok, but without looking its a crap shoot.

There is absolutely no substitute for getting the cooling passages in the head pressure tested. Magnaflux will not show internal cracks or the valve seat boring error mentioned above.
Jerry

The machine shop said they had not pressure tested the cooling passages, but they would be happy to do that. So I took the head back to them. I asked if they could tell whether the head gasket had been leaking and they said they did see a place where it looked like it had ( they said they had told me that when I first took the head to them. I have no recollection of that, but at least now I feel like we know what the problem was). After talking to my mechanic, I also told them to mill the head even though it was within 1/3000 of flat.

You sure the thermostat is working OK? Blown gaskets usually don't overheat that fsat. The ones I have seen, just blow coolant out the overflow and once it gets below the sender, the temp gauge reads cool or normal ( sending units will not read steam). Cracks in the head can blow coolant out like above, or suck coolant in and burn it, in that case, you can smell the exhaust. It will be kinda of sweet smelling.

If the exhaust is leaking into the coolant, that could it heat up really quick, but I would think that should blow coolant as well. You might really look into the exhaust ports for signs of something, anything that looks odd I would be leery of. Exhaust pressure in the ports ( after the valve ) is somewhat high for a short burst, nothing like compression in the cylinders. Dad had a Pontiac head rust out from the inside into the intake port. It didn't look like anything but a small white line till we poked at it. It turned in to a very thin walled 1/4" wide hole.

Joe

Joe - I had previously bought a new 160 thermostat and tested it with a candy thermometer.

I took the radiator to a different shop (in the big city- Dayton). They said after they cleaned it the flow increased about 25%. They also fixed a couple small leaks. They also recommended cleaning out the water passages in the block before I put the radiator back.
At the moment the head is off (at the shop getting milled, so the head will be nice and clean). Should I clean the block before I put the head back on, or is that even possible? If so, how? ( I've read the posts about the petcock in the block, so I know where it is and how I might have to remove it and use a coat hanger to get things started).

I'm picking up the radiator and head today. I'm assuming since I haven't gotten any responses to my last post that it is not possible for me to clean the block without the head installed.

With the head off, there will lots of places water will run, none of those places will be helpful. Cleaning that up will more work than I would want.

Very true, water will come out the deck area and run into the oil pan.

You could do it if you are careful, but it will easier with head on. Leave the thermostat out while flushing the block. If you can block the radiator hose inlet and outlets, and one of the heater hose outlets, you can use the last opening to pressure up the block with a garden hose. Then open or remove the petcock and flush out what you can. The petcock is the lowest and farthest back hole in the block, if it runs clean there, chances the block is pretty clean. With the outlets open, one of those solid brass hose nozzles with the pinpoint spray will work good to back flush the block through the petcock opening. Power washers also work really good.

Be sure to drill the 1/8" hole in the thermostat to let air out while filling the engine.

Joe

While the head is off, take a long, thin rod and poke around through the coolant passages to the bottom of the block and stir up the sediment as much as possible. Then install the head and back-flush the block through the drain petcock hole. Sometimes a thick layer of rust and crud accumulates around the bottom of the cylinders that no amount of in-the-vehicle flushing will dislodge- - - -it takes several hours with the bare block in a power washer cabinet with a strong, hot cleaning solution to clean it out. Good luck!
Jerry

Just wanted to give an update: After back-flushing the block with a garden hose/air hose (I found a post by Hotrod Lincoln, I believe), the engine is back together and is no longer overheating. Whether it was the new head gasket or back-flushing a ton of rust out of the block or having the radiator cleaned and repaired, I guess I'll never know. Thanks to everyone for their help.