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Location:
Brisbane
Registered:
July 2004
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7M-GE Compression results, dodgy??
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Wed, 15 December 2004 03:07
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Hi all
I have a MX83 cressida thats been overheating on longer drives (say over an hour). 2 mechanics said it wasnt a blown head gasket so I've replaced everything else  but over $1000 later problem remains (already done fan clutch, thermostat, cap, water pump should be ok (done earlier this year), flushed and new coolant, radiator was cleaned professionally earlier this year, replaced lower hose, and temperature sender unit for instruments).. head gasket was done earlier this year aswell, but as anyone who knows about the 7M engine, well... a blown head gasket is certainly a possibility, or maybe a small crack in the head? especially since ive noticed the car blows bubbles into the overflow tank (exhaust gas getting into radiator??) and there is a residue of what could be oil in the coolant (but NO signs of water in oil or under filler cap).
Did a compression test this morning:
Method used:
Drove car until it started playing up (ie: overheating).
Pulled inlet pipe off but left throttle body on.
Removed EFI relay (in engine bay fusebox)
Removed high tension coil wire.
Took out all spark plugs and wires. (hope this didn't matter as opposed to doing each cylinder one at a time)
Screwed in gauge, turned car over with throttle wide open until needle stopped moving. Repeated for each cylinder.
Results: (cylinder #1 is closest to radiator)
Cylinder 1. 15bar (215psi) ON RETEST 14.25bar (204psi)
Cylinder 2. 15bar (215psi) ON RETEST 15bar (215psi)
Cylinder 3. 14bar (200psi) retest not done
Cylinder 4. 14bar (200psi) retest not done
Cylinder 5. 13.5bar (193psi) ON RETEST 14bar (200psi)
Cylinder 6. 13.25bar (185psi) ON RETEST 14bar (200psi).
I looked in the toyota manual and it says minimum 128psi with a maximum difference of 14psi. (but these specs are assuming that the throttle body is removed, i didn't do this, just held the throttle open).
So if i've done this correct, does this mean that i have higher than normal compression (which might fit with the fact that the head had some work earlier in the year), but how come cylinder 2 seems bloody high (i tested this one 3 times, all with the same reading too..)
Thoughts please anyone?? These readings aren't at all what i was expecting and seem really high...What readings have others gotten on their 7M-GE's??
Cheers.
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Registered:
May 2002
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 00:41
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If your head has been over heating for some time now it would be likely that you've either warped your head or posibly cracked it. When they changed you head gasket, did they use a factory replacement or a HKS item. I'd use a HKS item as they are proven. I had mine replaced with a standard gasket the first tiem and it blew between cylinders 4 and 5 after about 1500km.
Also i'd ask if they faced the head with they had it off. Very important and in some extreme cases you might need to reface the block/deck too. You might want to have the head checked out whether it's softened up and not useable as this does occur with these 7M heads.
Not to worry as the stooges from toyota stuffed this up from the factory by not torquing the head down to the appropriate torque settings and virtually most of the 7M's had blown their head gaskets. It's a pitty as these motors are very strong when the gasket is done properly.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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I supported Toymods
Location:
Perth, Western Australia
Registered:
December 2002
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 05:04
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I'd be going back to the radiator if it heats up over a long time, even though it was cleaned, if you didn't install a filter in the top hose, it will probably be blocked again.
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Location:
Brisbane
Registered:
July 2004
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 05:21
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Thanks for your replys guys.. its been damn frustrating trying to fix this problem.
I'm fairly sure the mechanic used a genuine gasket and had the head faced (dont think the block was done, although shouldn't have been needed to).
I had wondered if there was some way that my auto was running hot and somehow acting like a heater element in a kettle when the fluid runs through the tranny cooler in the radiator, but seemed a bit farfetched..
So maybe take the radiator out and send it off to be disassembled and cleaned again? Spose it should be fairly cheap (last time it was only $80 for them to take the tanks off and clean the core).
I've been told by other cressida owners on the cressida forum (yes! we have our own forum...  - http://www.thermactor.com/forum/index.php) that it sounded like a crack in the head, but shouldn't this have shown up with a low compression in the check i did the other day ??(especially since i drove the car till it overheated, theoretically heating the car up to the point where the crack is opening up).
Any help would be appreciated..
Cheers.
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I supported Toymods
Location:
Perth, Western Australia
Registered:
December 2002
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 05:27
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| capableronTRD wrote on Thu, 16 December 2004 13:21 |
i drove the car till it overheated, theoretically heating the car up to the point where the crack is opening up
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You realise metal expands with heat, not contracts???!
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Registered:
May 2002
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 05:30
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Have you performed a Leak Down Test? It's similar to a compression test, but uses the pressure of an oxygen cylinder to test for leaks and is more acurate (from my understanding). A good mechanic should be able to perform one of these and it'll definitely show up any leaks or imperfection in the chamber.
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Location:
Brisbane
Registered:
October 2002
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 07:33
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call melvins automotive, they are in yarowee st currajong, u need a car that wont overheat in t'ville too 
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Location:
Brisbane
Registered:
July 2004
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Re: 7M-GE Compression results, dodgy??
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Thu, 16 December 2004 09:23
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My thinking was that a crack was possibly opening up when the metal expands, but hey i'm definatley no expert!
Hmm..i suppose i really SHOULD get as conclusive result as i can before going in and ripping the head off (which looks like a B*tch with these engines!)...i'll definatley chase this up. THanks.
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