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 Is my head gasket leaking or not??
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Charles
Grease Monkey

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Posted - Sep 05 2009 :  14:10:24  Show Profile  Reply with Quote
For over six months now, my '81 745i (bored out to 3.5 liter) has had what I believe to be a head gasket leak, but I am not sure enough to spend the $ for a new gasket set, or put in the hours to do it...

New 75C thermostat, recent water pump (bearing failed, after these symptoms started).

It will run normally for hundreds of miles, even in 90 degree weather, and the gauge stays exactly nailed 2.5 marks above the blue (it was 3 ticks with the 80C stat).

UNTIL I get on the boost. Even for five or ten seconds. Then within 30 seconds whether I let off the gas or not, the heater goes dead cold, it overheats to the top of the gauge, and pukes all the coolant out the overflow hose!

This implies to me that combustion gases are entering the water jacket under pressure and displacing the coolant...

After shut down and refilling the coolant, it will run properly again for another 1000 miles. But not being able to use more than 1-2 psi boost is getting old... especially since I run 15 psi, extra injectors, and even a little nitrous for quicker spool up ;)

I think I can smell exhaust in the expansion tank, and it is using coolant slowly. But there is no coolant in the oil and no oil in the coolant, no bubbles in the expansion tank, no steam in the exhaust! All six plugs are the same color too.

Have others seen a head gasket that only leaks under boost?
thanks
Charles
'81 745i
also can email me direct at: charlesmorris800 at centurytel dot net

Hit Man X
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Posted - Sep 05 2009 :  21:54:36  Show Profile  Send Hit Man X an AOL message  Send Hit Man X an ICQ Message  Click to see Hit Man X's MSN Messenger address  Send Hit Man X a Yahoo! Message  Reply with Quote
May have more issues if you are spraying a turbocharged motor...

Are you pulling 2-3deg per 50hp shot? Do you still have that tiny 130lph inline fuel pump?

Extra injectors from what/where?

This is my sig...

Four 745i! One '83 and three '85...I am a glutton for punishment.
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Hit Man X
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Posted - Sep 05 2009 :  22:12:34  Show Profile  Send Hit Man X an AOL message  Send Hit Man X an ICQ Message  Click to see Hit Man X's MSN Messenger address  Send Hit Man X a Yahoo! Message  Reply with Quote
Oh and the motors prefer the 80C thermo... stock gauge is crap.



Have you checked the oil for coolant? And the coolant for oil?



Only experience with a dead gasket on a turbocharged gas motor was on my pal's old Turbo Buick. It was dead obvious... white smoke ALL the time from the tail pipe until we rebuild the top end.

We can discuss faster spool from the Ljet later... you really need a good electronic boost controller for this and if you can, find a higher stall torque converter. Plus an exhaust without restriction.

This is my sig...

Four 745i! One '83 and three '85...I am a glutton for punishment.
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greg_mazur
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Posted - Sep 06 2009 :  05:24:16   View greg_mazur's Photo Gallery  Show Profile  Reply with Quote
You probably need a head gasket, or do so now with the over heat situation you experienced.
Other than that I once had a rotary that would do the same thing with absolutely no oil in the coolant no coolant in the oil and heater dead, "only at high rpm" would react as you described. Problem was the coolant hose collapsing causing cavitation at high rpm, which quickly ran dry the pump and blocked the flow of coolant. Then when you slowed down the engine temp would return to normal. When you get on the boost you also bring up the rpm's, which increases the coolant flow, and weak hoses suck shut. Can come from a higher speed water pump pulley without hose upgrade. If you could bring up the rpm's without boost and see if you get the same results, you could eliminate the pressure question and head gasket issue. If so start looking at the entire coolant circulation system. Good luck....your Labor Day may be just that lots of labor!

Edited by - greg_mazur on Sep 06 2009 05:25:42
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Charles
Grease Monkey

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Posted - Sep 06 2009 :  10:51:44  Show Profile  Reply with Quote
Thanks for the responses so far...

I had thought about collapsing lower hose, but it's firm to the touch even when hot, and revving the engine while watching the hose does not visibly suck it in.

I'm pretty sure I know the answer, just hoping for a simpler solution than pulling the head

Regarding the modifications - I am using a stock 3.5 liter head gasket, 11-12-1-730-223 and it's been in there since 1993 when I blew one (pinging while tuning my Bell rising-rate fuel pressure regulator).

The extra injectors are two large ones spraying into the "charge pipe" (the cone that passes over the valve cover). Microprocessor controller of my own design. It only kicks in above the stock 8 psi boost level.

I plumbed a fitting into the top of the wastegate and added a dashboard adjustable 0-20 psi regulator (thus allowing boost to be dialed in from stock 8 psi up to a theoretical 28 psi).

Exhaust is two 2.5" pipes straight back to only a stock rear muffler. Back pressure is unmeasurable on a 0-15 psi gauge, even at 15 psi boost. That stock muffler flows quite well and is quiet too.

Nitrous is one 20 to 40 hp Fogger nozzle farther up the intake tract and I am not using it currently. The fuel system has been through several iterations and currently has a Walbro GSS392 (255 lph) in-tank pump. That is more than enough fuel and I have a cockpit pressure gauge to confirm. Ignition is an MSD-6A with Boost Timing Master currently set at 0.8 degree retard per psi. I have the check valve (dump to the PCV hose) removed and plugged, connecting both vac advance hoses "straight" to their respective throttle body ports, so when there is boost in the manifold the distributor neither advances nor retards, since it is subject to the same pressure on both sides of the diaphragm ;)

Anyhow this was all working fine for many years at 15 psi boost on 92-93 octane pump gas (can't run over 11 psi with the nitrous or my Metric Mechanic "Hi-Torque" clutch starts slipping anyway).

Last year I was passing a line of cars and the vac hose blew off the Boost Timing Master and the resultant heavy detonation before I could let off the gas undoubtedly weakened the gasket. I have good forged 8:1 pistons so they survived. Would rather lose a gasket than a piston top!

thanks
-Charles
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Hit Man X
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Posted - Sep 06 2009 :  16:33:20  Show Profile  Send Hit Man X an AOL message  Send Hit Man X an ICQ Message  Click to see Hit Man X's MSN Messenger address  Send Hit Man X a Yahoo! Message  Reply with Quote
Okay good, you have planned out the extra power. Most just believe all they read and believe the stock fuel system can support 500hp LOL Biggest place to start is with the fuel pump... if you are unable to put the fuel at the rail, the best injectors in the world will not do you any good.

Yup on the factory exhaust system, very efficient. You can see right thru the stock rear muffler. Two of my three were choked down to a SINGLE 2" in/out cat! Talk about restriction city. My '84 has the entire factory system which is great. I just need to find some more visually appealing tips.

On the 6A box, did it help idle/low speed performance at all? I have one laying around (6AL actually with rev limit) and am considering adding it as the bank-to-bank EFI loads up cylinders due to its nature... just how a carb acts.



On the gasket, just figure if it has failed... you received 16 years from its service. I ran it past my pal and he believes the gasket has failed too...

Ever run a used oil analysis to check your contamination levels?

This is my sig...

Four 745i! One '83 and three '85...I am a glutton for punishment.
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Charles
Grease Monkey

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51 Posts

Posted - Sep 06 2009 :  20:41:28  Show Profile  Reply with Quote
Yes, the MSD helped. The stock Bosch ignition is very weak (as evidenced by the piddling .028" plug gap from the factory). It definitely started easier, idled smoother and (before I rebuilt the badly worn engine) even smoked less.

I wonder if those test kits (to tell if there are HC in the coolant) are any good... before I order a $120 head gasket and start tearing it down?


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Hit Man X
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Posted - Sep 06 2009 :  21:27:16  Show Profile  Send Hit Man X an AOL message  Send Hit Man X an ICQ Message  Click to see Hit Man X's MSN Messenger address  Send Hit Man X a Yahoo! Message  Reply with Quote
Thanks for the MSD info, I will have to slap that on there when I get the car back on the road... dash is out now! Hopefully it will work on the Motronic cars too. But I am not too sure as I am far from an electronics expert, still trying to learn.

Oh yeah, the oil kits work great. Black Stone Labs is the place to go... figure $20 or so.



I like the 3.5L idea in there, Don (dnliii) told me of this and I finally sourced myself a Motronic block to go into my Ljet also.

This is my sig...

Four 745i! One '83 and three '85...I am a glutton for punishment.
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Charles
Grease Monkey

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Posted - Sep 09 2009 :  18:08:33  Show Profile  Reply with Quote
I didn't need a 3.5 liter block. I had my 3.2 liter sonic-checked and there was plenty of meat even with the 2mm (.080) overbore.
Even a stock 3.5 block should be checked for core shift (thin walls) especially on the major thrust surfaces, if you are planning on big boost...

FYI, BavAuto has the -223 gasket for $119.95 but the -224 (slightly thicker) has to come from the Fatherland and would take a while.

-Charles
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Hit Man X
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Posted - Sep 09 2009 :  23:52:38  Show Profile  Send Hit Man X an AOL message  Send Hit Man X an ICQ Message  Click to see Hit Man X's MSN Messenger address  Send Hit Man X a Yahoo! Message  Reply with Quote
Well I paid $100 for the used block I am just going to run it until something fails.

I take it you are yanking the head now?

This is my sig...

Four 745i! One '83 and three '85...I am a glutton for punishment.
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Charles
Grease Monkey

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51 Posts

Posted - Oct 23 2009 :  16:36:32  Show Profile  Reply with Quote
OK! Finally yanked the head today... got tired of losing coolant constantly, overheating even when driving like an old lady. The job was every bit as much a PITA as I had remembered, including a face and eyeful of nasty, acidic coolant as I removed the block drain plug.

Sure enough, the fire ring on #4 cylinder was pushed out quite a ways. Obviously the source of entry for hot combustion gas into the water jacket. The carbon wiped right off the piston top, too, whereas it's pretty baked on the other five.

I was ready to put the new head gasket on and bolt it back together - but on close inspection, unfortunately there is a very tiny pitting of the head surface right where the leak was. It may clean up with a resurface but more likely should be TIGed and then a light cut for flatness. I am going to take it to Metric Mechanic (they're only a couple hours away from me and I am not going to trust my $$$ head to Chevy Good-Ole-Boys-R-Us machine shop!)

Naturally the fourth and last turbo-to-manifold bolt broke off in the turbo flange... so much for anti-seize paste (of course it HAS been 15 years). Would you believe that M10x95 bolt is $62 list and $51 from Bavauto!! Once I get the piece removed, I am going to buy a 100mm bolt from McMaster-Carr ($7.42 for a pack of five) and cut off 5mm. You can see the busted off piece in the pictures, too.







Guess I will be driving the old pickup for a while!

-Charles
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