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Thread: 7mgte overheating problem, no symptoms of bhg

  1. #1
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    7mgte overheating problem, no symptoms of bhg

    Hey there, I have a 1988 Toyota Supra Running a Modified 7mgte in it and it keeps overheating but only if I hit boost! If I never hit boost it doesnt over heat.

    I was originally told by the previous owner that he thought the head gasket was going again but it doesnt make sense as it shows zero symptoms of a BHG and Im not losing coolant! (Aside from it puking everywhere if the car overheats.)

    The only things I can think of were that he said it started over heating and they removed the thermostat? Very odd if you ask me, maybe it was broken and not regulating temperture?

    Ive also heard that the stock Rad for the 7mgte isnt enough to handle over 300 whp, Im going aluminium anyways so this is getting upgraded regardless, hopefully it might solve the issue, maybe a better cap would help as well.

    The previous owner was only running water as well! I personally wouldnt have done that and feel like maybe it corroded something and clogged the rad. Once again, coming back to the rad.

    It puffs light white smoke now and again but I cant find any collant in the oil, oil in the coolant, strange compression or even problems idling.

    There is a boost leak somewhere I also need to resolve, but I dont think that would affect it.

    Does anyone have an insight on this at all? Im hoping it is an easy fix and i dont need a top end rebuild haha.

    I will be documenting all fixes to see where it takes me, hopefully this thing doesnt blow up!


    Recent maintenance:
    Headgasket, head and block decked, full top end (valve stem seals, steam cleaned, shimmed, etc) at 174xxxkm

    FULL BUILD:


    Engine mods:
    Ported & polished head
    K&N cone filter
    Aftermarket charge pipe
    Lexus 1UZ air flow meter
    RC 550cc injectors
    CT26 turbo, internally modified and bored to 57 trim
    BIC divorced downpipe, recirculated wastegate
    Test pipe
    Apex'i exhaust
    Whole exhaust is 3" to 4.5" tip
    Cometic steel headgasket
    ARP studs
    Aluminum rad pipes

    Chassis mods:
    Eibach springs
    Tokico illumina adjustable struts
    HKS polyutherene bushings
    Front strut bar
    Stainless steel braided brake lines
    Hawk HP+ pads
    Slotted & cross drilled rotors
    HKS TEMS suspension controller
    Targa X brace (weezl wing)
    Stage 2 clutch and plate
    OEM clutch master and slave cylinder
    H4 headlight conversion

    Last dyno pull was 500whp at 21psi on hopes and dreams years ago, running 12-14psi street use at around 400-420 whp, has had some minor work since then.

  2. #2
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    Reserved

    UPDATE:

    - Car now doesnt seem to have boost leaks, still hit fuel cut but whatever, doesnt matter, all vacuums were sealed.
    - 100% running rich, there is no way to control these 550 injectors
    - Rad seems to be clogged, very large temp differnces in piping that should have none.
    - Still no sign of BHG ( Thank god)

    This car is one hell of a ride, whoever built it did some weird ****ing ****.

    UPDATE 2:

    - Jimmy rigged the window washers as sprayers for the rad
    - Think the water pump has failed, have a new one, will see how it goes
    - Also getting new RAD soon, hopefully that solves some problems

    Outside of this, Im not enjoying the car all to much. I dont like turbos to begin with and boost only comes on at 4500 rpm which gives for a bad feeling throttle response.
    Last edited by SweetBB; 08-23-2015 at 11:20 PM. Reason: update

  3. #3
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    Overheats when? Like driving like an asshole for 10min, or just 1 pull on boost?

    Stock rad lol. Get something thicker and report back.


    RETIRED

  4. #4
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    It could totally be a clogged rad, but it sounds a hell of a lot like the head is lifting a bit/headgasket failing under boost. Try retorquing head studs as it's a fairly common issue afaik and is usually the precursor to bhg on 7m.
    If there's one thing I've learned from the first two thirds of the MC Hammer Biography, it's that money never runs out.

  5. #5
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    I've heard that the thermostat is important for building pressure inside the block/head - this pressure prevents the coolant from vaporizing. try putting a thermostat in.

    Also what coolant mix do you have? straight water is terrible.

  6. #6
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    Was it decked & planed with stones or inserts? Makes a difference. Stones are great... if you're rebuilding a 305.

  7. #7
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    Impeller fall off waterpump?
    1987 Corolla GTS Hatch | 1985 Corolla GTS Coupe | 1987 Corolla GTS Coupe | 1992 Tercel CE | 1992 Paseo | 2003 Corolla CE | 1974 Corolla 4 Door | 1978 Corolla Coupe | 1979 Corolla Hatch SR5 | <3||||||1990 Miata |||||| <3
    I like Toyota's wanna fight about it?

  8. #8
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    Quote Originally Posted by JungleMatic View Post
    Overheats when? Like driving like an asshole for 10min, or just 1 pull on boost?

    Stock rad lol. Get something thicker and report back.
    No, I drive it under 3k rpm and have no problems. It isnt until I hit boost that it overheats or I go on the highway (5th gear at 2500 rpm)

    Quote Originally Posted by Chewy View Post
    It could totally be a clogged rad, but it sounds a hell of a lot like the head is lifting a bit/headgasket failing under boost. Try retorquing head studs as it's a fairly common issue afaik and is usually the precursor to bhg on 7m.
    Heads are torqued to 80, Im gonna be re torquing them to 100

    Quote Originally Posted by Sparkie View Post
    I've heard that the thermostat is important for building pressure inside the block/head - this pressure prevents the coolant from vaporizing. try putting a thermostat in.

    Also what coolant mix do you have? straight water is terrible.
    Yes straight water is terrible, I went to prestone 50/50 and it seems to be working way better, no leaks and no oil in coolant after running it for a day or so, or vice versa. that I could see at least.


    Buying a new thermostat today, and going to be putting it in. Ordered a new rad hopefully that can solve my issue.

  9. #9
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    put a thermostat in it and bleed it properly, sounds like air in the system, i had a Mk3 7mgte with all the various hoses on that thing bleeding can be a a pain in the ass.

    Geard.
    Collecting Parts...

  10. #10
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    Dang BHGs
    1JZ 1984 Celica GTS
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    ? 1972 Celica race car

  11. #11
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    Quote Originally Posted by Geard View Post
    put a thermostat in it and bleed it properly, sounds like air in the system, i had a Mk3 7mgte with all the various hoses on that thing bleeding can be a a pain in the ass.

    Geard.
    Bleed + Thermostat, still hasnt doen the trick. Rad seems to be clogged somewhere though as the pipe that connects the rad to the tstat is 40 degrees cooler than the rad!

  12. #12
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    the upper hose flows coolant from the tstat housing to the rad I thought... that would imply a water pump or thermostat failure if that hose isnt hot.

    but I could be wrong, someone else help.

  13. #13
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    Quote Originally Posted by SweetBB View Post
    No, I drive it under 3k rpm and have no problems. It isnt until I hit boost that it overheats or I go on the highway (5th gear at 2500 rpm)



    Heads are torqued to 80, Im gonna be re torquing them to 100
    Unless you know of a bunch of people who have done the same, I wouldnt be the pioneer down this road. 75-80 is the revised spec over the years, if you're just choosing 100 and goin for it, its possible you're just causing yourself more problems.

    Retorque to 80.

    Brett
    '87 AE86 - GTSR5 - Daily Driver
    '72 RA21 Celica - 'Ill build it one day'
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  14. #14
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    Quote Originally Posted by celica-fiend View Post
    Unless you know of a bunch of people who have done the same, I wouldnt be the pioneer down this road. 75-80 is the revised spec over the years, if you're just choosing 100 and goin for it, its possible you're just causing yourself more problems.

    Retorque to 80.

    Brett
    I havent torqued them yet, a few people told me I should but I didnt go through with it.

  15. #15
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    FYI, a T-stats does not affect pressure. Rad cap does. Check/Replace rad cap if system does not get pressure at operating temp (rad hose doesn't get firm). The system does need to be purged of air too.
    Bryan
    DK Moderator




  16. #16
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    Had a similar issue with my M3. Didn't purge it well enough and the T-stat was not bathed in water and therefore did not receive enough heat to open. Upper rad hose was cold but the engine got plenty too hot.
    1JZ 1984 Celica GTS
    1UZ 1981 Corolla sedan
    ? 1972 Celica race car

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