Overheating/coolant loss on long trips

87hilux7mge · 04-19-2011, 07:00 AM

cre, ive been curious about this too. the two motors i picked up for my project (88 jdm 7mge, 90 cressida 7mge) both tested high compression while cold! the jdm motor ranged 185-193, the cressida ranged 20-195 (3 cyls were completely boned). when i disassembled the motors, they both had the same type of pistons, but when i compared them to my new pistons, they had considerably less dish in them, almost flat tops. i was concerned that id gotten turbo pistons, but compared them with my freind john's pistons, and mine were definitely for N/A. so somewhere, toyota got a wild hair up their bum and put high compression n/a pistons in some motors.

i had no luck finding these pistons anywhere.. but that seems to be in the same compression range as mine, since his was warm.

sorry that was a lil off topic...

cre · 04-20-2011, 04:11 PM

I'm going to hazard a guess that no one's bothered to get the part number and manufacturer off of one of these? It's cast inside.

Have either of you measured the dish volume?

87hilux7mge · 04-20-2011, 07:27 PM

i did a ruff measure and the flat top is almost 1/16th deep, not counting valve relief. my new pistons are 1/8th. i cant recall what the dish is on turbo pistons.

i can get the part # this weekend and post it up sometime next week. im ashamed to say, i never thought to get the number and cross reference it from the factory...fail.

i will certainly check it out though!

dannydavi · 04-22-2011, 08:11 PM

Quote:

Originally Posted by 87hilux7mge

cre, ive been curious about this too. the two motors i picked up for my project (88 jdm 7mge, 90 cressida 7mge) both tested high compression while cold! the jdm motor ranged 185-193, the cressida ranged 20-195 (3 cyls were completely boned). when i disassembled the motors, they both had the same type of pistons, but when i compared them to my new pistons, they had considerably less dish in them, almost flat tops. i was concerned that id gotten turbo pistons, but compared them with my freind john's pistons, and mine were definitely for N/A. so somewhere, toyota got a wild hair up their bum and put high compression n/a pistons in some motors.

i had no luck finding these pistons anywhere.. but that seems to be in the same compression range as mine, since his was warm.

sorry that was a lil off topic...

I took out the thermostat to make sure it wasn't that. The rad was replaced a little over a year ago, although I haven't ruled that out yet. The fan clutch I replaced this weekend because the checks I did on mine seemed like I should replace it... but still overheating

When I took the rad off I flushed it best I could and it seemed to be flowing just fine. Also felt the upper and lower hoses and noticed the bottom was cooler than the top, but still warm.

after looking more into it, it seems on long trips is only time it occurs, around town I'm golden.

cre · 04-22-2011, 08:27 PM

Stock dish is 3mm below the crown. I don't know what's up if you've actually got different pistons; Usually the high readings are the result of oil draining into the cylinders from the plug galley.

Danny, what's your timing set to? Retarded timing (both mechanical and ignition) will cause higher engine temps.

dannydavi · 04-22-2011, 08:40 PM

Quote:

Originally Posted by cre

Stock dish is 3mm below the crown. I don't know what's up if you've actually got different pistons; Usually the high readings are the result of oil draining into the cylinders from the plug galley.

Danny, what's your timing set to? Retarded timing (both mechanical and ignition) will cause higher engine temps.

Well I have the JDM engine so I have no clue what pistons are in it. I haven't checked timing since I put it in, I'll have to check again. I might just take it to a shop instead of dealing with this headache, I'll deal with a wallet ache instead...

cre · 04-22-2011, 09:07 PM

156psi optimum, 124psi min. If your engine was PERFECT and just had a lot of carbon buildup you still wouldn't see much past the lower 160's.

JDM uses the same pistons.

That's GE by the way; GTE is supposed to be about 15psi lower.

87hilux7mge · 04-22-2011, 09:28 PM

piston dish that on the pistons i bought was exactly as you said cre, 3mm, just under 1/8th inch (if my math is correct...??). i do remember gauging the other pistons and they are just under 1/16th inch, prolly around 1.5mm. so ill have to figure out what the serial number is today. ill get one and post back soon.. im very curious about these two sets of pistons i have...might have to use them in another build if i can find a good block. high compression 7mge

dannydavi · 04-22-2011, 11:47 PM

so just an update, block tested it today and it is blown

I hate life

04-19-2011, 07:00 AM	#1
87hilux7mge walbro fp Join Date: Dec 2010 Location: spokane Posts: 479	cre, ive been curious about this too. the two motors i picked up for my project (88 jdm 7mge, 90 cressida 7mge) both tested high compression while cold! the jdm motor ranged 185-193, the cressida ranged 20-195 (3 cyls were completely boned). when i disassembled the motors, they both had the same type of pistons, but when i compared them to my new pistons, they had considerably less dish in them, almost flat tops. i was concerned that id gotten turbo pistons, but compared them with my freind john's pistons, and mine were definitely for N/A. so somewhere, toyota got a wild hair up their bum and put high compression n/a pistons in some motors. i had no luck finding these pistons anywhere.. but that seems to be in the same compression range as mine, since his was warm. sorry that was a lil off topic... __________________ 87 toyota 4x4 single cab short box pickup, 7MGZE.

04-20-2011, 04:11 PM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	I'm going to hazard a guess that no one's bothered to get the part number and manufacturer off of one of these? It's cast inside. Have either of you measured the dish volume? __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

04-20-2011, 07:27 PM	#3
87hilux7mge walbro fp Join Date: Dec 2010 Location: spokane Posts: 479	i did a ruff measure and the flat top is almost 1/16th deep, not counting valve relief. my new pistons are 1/8th. i cant recall what the dish is on turbo pistons. i can get the part # this weekend and post it up sometime next week. im ashamed to say, i never thought to get the number and cross reference it from the factory...fail. i will certainly check it out though! __________________ 87 toyota 4x4 single cab short box pickup, 7MGZE.

04-22-2011, 08:27 PM	#5
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	Stock dish is 3mm below the crown. I don't know what's up if you've actually got different pistons; Usually the high readings are the result of oil draining into the cylinders from the plug galley. Danny, what's your timing set to? Retarded timing (both mechanical and ignition) will cause higher engine temps. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

04-22-2011, 09:07 PM	#7
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	156psi optimum, 124psi min. If your engine was PERFECT and just had a lot of carbon buildup you still wouldn't see much past the lower 160's. JDM uses the same pistons. That's GE by the way; GTE is supposed to be about 15psi lower. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

04-22-2011, 09:28 PM	#8
87hilux7mge walbro fp Join Date: Dec 2010 Location: spokane Posts: 479	piston dish that on the pistons i bought was exactly as you said cre, 3mm, just under 1/8th inch (if my math is correct...??). i do remember gauging the other pistons and they are just under 1/16th inch, prolly around 1.5mm. so ill have to figure out what the serial number is today. ill get one and post back soon.. im very curious about these two sets of pistons i have...might have to use them in another build if i can find a good block. high compression 7mge __________________ 87 toyota 4x4 single cab short box pickup, 7MGZE.

04-22-2011, 11:47 PM	#9
dannydavi 12psi boost Join Date: Mar 2007 Location: Sacramento, Ca Posts: 373	so just an update, block tested it today and it is blown I hate life __________________ '86.5 Supra - A/T - N/A - JDM Useful Sites: ToyoDIY.com ToyotaPart.com MKIIITSRM

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