DIY OM603 head pressure test - head good? - PeachParts Mercedes-Benz Forum

ah-kay · #1 06-09-2018, 12:54 PM

Well, I got this head from a junk yard. It was removed by others and left next to the car. I bought it not noticing the cracks between the valves in 3 cylinders. May be it was the reason that it was left there. I decided to challenge myself and pressure test the head for fun. I used coins to block all coolant passages with JB weld, block the big coolant outlet by putting a plate there and screw the hose connector back on. Actually it is quite easy to do and spend very little time. Submerge the head in water and pressurize the head to 50psi. NO BUBBLES. It also holds vacuum if I pump it with a vacuum pump. All in all, I think it is good. The only shortcoming is I did not use hot water. What do you guys think? Good to install?

btw: you can notice the cracks between valves if you look closely. It doesn't seem to matter in this case, contrary to conventional beliefs.

jay_bob · #2 06-09-2018, 01:27 PM

I suspect that under the dynamics of a running engine things are quite different. Remember you’re dealing with 300-350 psi of compression (ideally) and the head is heated to approximately 80 C/180 F.

I think these two factors are what make head cracks leak, not hitting it with 50 psi air in ambient temperature water.

My opinion which is probably worth about equal to the $0.42 I see glued to that head...

ah-kay · #3 06-09-2018, 02:13 PM

The professional is also pressuring the head to Max 400kpa which is about 58psi. The condition is similar except in hot water. I ramped it to 80psi and still no bubbles. I may be wrong but I am comfortable with my testing.

Diseasel300 · #4 06-09-2018, 04:26 PM

Cracks between valves = junk. It isn't a question of will it leak, it's how badly does it leak? The pressure in the cylinder is much higher than the 350-400PSI of compression when the fuel ignites.

ah-kay · #5 06-09-2018, 09:24 PM

Quote:

Originally Posted by Diseasel300

Cracks between valves = junk. It isn't a question of will it leak, it's how badly does it leak? The pressure in the cylinder is much higher than the 350-400PSI of compression when the fuel ignites.

I beg to differ. I expect any crack, no matter how minute, would show bubbles at 80psi.

Diseasel300 · #6 06-09-2018, 10:20 PM

Quote:

Originally Posted by ah-kay

I beg to differ. I expect any crack, no matter how minute, would show bubbles at 80psi.

Hey, your time, your money. You do what you want. Considering how the #14 heads are the most common to leak and cracks in a casting are NEVER a good thing, whatever...

Go ahead and throw it on the car and see how it works. At best you'll get some life out of it before it starts vapor locking the cooling system. At worst you'll have wasted a head gasket, time, and money on a POS head. Your call...

ah-kay · #7 06-09-2018, 11:10 PM

Quote:

Originally Posted by Diseasel300

Hey, your time, your money. You do what you want. Considering how the #14 heads are the most common to leak and cracks in a casting are NEVER a good thing, whatever...

Go ahead and throw it on the car and see how it works. At best you'll get some life out of it before it starts vapor locking the cooling system. At worst you'll have wasted a head gasket, time, and money on a POS head. Your call...

I have done a number of head replacements and they are all #14. Please please don't make out #14 like a monster. There are still a lot of om603 engine running around with#14. I have put heads with hairline cracks back on and they run Ok. I decide to do a diy pressure test on this one and I find it to be good, in my opinion. I really can't see problem with this head if it holds 80psi.

I understand it is my car, my time and my money. I just want to share my experience on how-to with some improvisation. I appreciate all your comments.

97 SL320 · #8 06-11-2018, 10:14 AM

Quote:

Originally Posted by Diseasel300

Cracks between valves = junk. It isn't a question of will it leak, it's how badly does it leak?

Not always. I'd have to dig around for some manuals but cracks between the valves are common and there is an acceptable limit. In general, cracks here are only acceptable if they don't reach the valve seats and are under a certain length.

Quote:

Originally Posted by Diseasel300

The pressure in the cylinder is much higher than the 350-400PSI of compression when the fuel ignites.

Cylinder pressures are high only for a very short time. Map out a cylinder pressure curve and you will see.

Using 50- 90 PSI to check for combustion to coolant leaks is a very valid test that is used my actual automotive machine shops.

funola · #9 06-11-2018, 10:20 AM

Quote:

Originally Posted by 97 SL320

Not always. I'd have to dig around for some manuals but cracks between the valves are common and there is an acceptable limit. In general, cracks here are only acceptable if they don't reach the valve seats and are under a certain length.
........................

If the cracks between valves are within limits, there are outfits that can machine away the cracks, weld in fresh aluminum, more machining, then do a valve job.

tjts1 · #10 06-09-2018, 05:27 PM

Is this a #14 head? Take close-up pics of the space between the valves and prechamber on cyl 4, 5 and 6.

jt20 · #11 06-09-2018, 07:01 PM

Visible cracks do not always mean they go all the way through.

It could be fine, but certainly not great, and is way more likely to crack further.

Temperature is very important for this test. I would not install it without testing at near boiling temp.

Thats a lot of work.

ah-kay · #12 06-09-2018, 09:20 PM

Quote:

Originally Posted by jt20

Visible cracks do not always mean they go all the way through.

It could be fine, but certainly not great, and is way more likely to crack further.

Temperature is very important for this test. I would not install it without testing at near boiling temp.

Thats a lot of work.

I like your comments. It is a #14 head.

tjts1 · #13 06-09-2018, 10:01 PM

Quote:

Originally Posted by ah-kay

I like your comments. It is a #14 head.

You're playing with fire. If it's not leaking yet it will eventually. If you can't see any cracks on close inspection the only real test is to run it on the engine and see if it pressurizes your cooling system. The later #17 and up heads are substantially redesigned. The deck of the head is much thicker. I wouldn't bother with a "good" #14 head.

Diseasel300 · #14 06-09-2018, 11:32 PM

I'm not knocking the #14 head. I'm running one on my own car. When the head came off for valve work, it was inspected for cracks and pressure tested. It passed and got re-used. I'm certainly not afraid of a sound #14 head and I think the paranoia surrounding them is way overblown.

THAT SAID, cracks are NOT a good sign on the #14 casting, if it isn't leaking now, it will be soon. It's a lot of effort and time to pull and replace the head, not a job to look forward to.

ah-kay · #15 06-10-2018, 12:00 PM

These are links which show how pressure test is done. As long as there is no bubbles, the head is good to go. It may not be necessary to test with hot water. Please understand hairline cracks do not mean cracked head. One word of caution for any one who tries this. Wear safety goggles. If the glued coin popped under pressure, it can fly anywhere.

https://youtu.be/A26KfDj6wAM
https://youtu.be/VJL-hcC_CBA
https://youtu.be/x_OHmyTYDBQ