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7M mkII with overheating issues - problem solved

4540 Views 9 Replies 8 Participants Last post by  Suprajayaz
Many mkIIs that have the 7M in then seem to over-heat easily when driving more than 60-70mph. I've found that this is not really the case, the mkII water temp. gauge is too sensitive for the mkIII sending unit. The normal operating temp for the mkIII is 160-230F, however the mkII reads normal from 150-190F and any thing more than 195F and the gauge is climbing for H very fast.

The solution to 'over-heating' 7M powered mkIIs is to install an aftermarket water temp guage and make sure that you do not go over 220F OR use the mkII water temp sending unit on the 7M motor. I personally opted for the aftermarket temp guage. Hope this helps some of you who are chasing a phantom problem.
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where are your # from ive never had a problem with my 7m gte in my mk2 with running hot. i just checked the trms and you #s are of
mk2 page

mk3 page

if the thremostats the same then y would the car run hotter?
if your car is running that hot then shomething els has to be the problem.
im not trying to shoot you down i just dont know where you got your info from. Dave
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Yes, the t-stats (assuming 190F) should open at aprx. the same temperature, however this is not the issue that I am attempting to deal with. I know of five 7M mkIIs that have perfectly good running engines (MHG, ARP studs, 3 core custom built rads. and no leaks anywhere) that seem to have an over heating problem - and got the feeling that 5 swaps in a row cannot be bad. So I did a little research. Trent from MVP motorsports has a high hp mkIII and knows his car inside and out - he told me that the mkIII temp gauge will read normal up to 230F. That tells me that the sending units differ a bit from the mkII to the mkIII.
Also, if you live in an area that hardly gets above 85-90F then everything will appear normal. However, if you live in TX, FL, AZ, NM, or some other hot place (Atlanta, GA for me) and run the a/c frequently the temp gauge will rise quickly and the car may not necessarily be overheating.

Just thought that I would share what I have learned and try to save some other people time and money chasing a problem that may not really exist with their swap.
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thats cool like i said i just didnt know where you got your #s from --- im in california and it gets well over 100 hear but as i said befor iv never had a problem with getting hot and im on a stock 5m rad so i dont know .
I'm having this problem with mine. I'm going to try the mk2 sender like you said, it makes sense. I have the 3row rad, etc. and the engine shows no signs of overheating and runs fine. Thanks for the info.
I would recommend running the 82 C thermostat and using Redline Water Wetter for added protection in the warmer climates. And having the cooling system reverse flushed, new radiator cap and checking to see if the radiator is having the proper flow ( not clogged).

I tow a 5th wheel trailer with my Cheby PU and if I use a 195 F degree thermostat the temp pushes upwards of 215-225 F. I use a 180 degree thermo the temp never goes over 205 F.
7MGTE has LOWER normal operating water temp than 5MGE. Opposite of what you are suggesting.

5MGE = 88°C
Early 7M = 82°C
Late 7M = 87°C


Andy S
New to forums: Hello everybody..., I have the silver supra w/7mgte with a/c, fluidyne radiator, stock hydro fan, and three additional electric fans w/shroud running with a/c on going to Palm Springs in the summer temperature in the 115s+, and yes the needle does read just below the red zone,I was assuming it is early signs of blown headgasket,or the high cruising rpm(3800) cause the higher heat, but (engine sounds ok,and coolant is not spitting out of the resevoir),definitely ok when not running the a/c (tons of load with a/c on). When I remove the head to get it rebuilt, the gasket was fine. My motor now has the hks metal bead gasket, I went to the vegas meet with the a/c on going up/down hill no problem, but have not had the chance to go to palm spring in the 115+ degree to see if that problem still exist.
I'll have to agree with chris for the time ..
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Still running the stock rad for me with twin electric fans and I have a heat problem. I can run without a/c on most days without problem but turn on the air and I'm in trouble. I need either the three core or the aluminum rad from the group buy or something. I'm going to look into this.
I ended up with a Don C. custom 3 core radiator - using stock shroud + new 7mgte fan and clutch, which helped 90% of the high temp issue in my 7mgte Mk2. I removed the plastic cover under the pass side headlight, added a dryer hose from the driver side air dam opening to the radiator and also made a 'scoop' about 4.5"x12" that directs air from under the car up to the radiator.. kinda like how Vette's do. Water wetter did nothing for me, so now I just run ~ 60% water / 40% antifreeze. Full boost, up long hills in Arizona 110F+ days and temp needle goes from straight up (normal in my car) to about the 5/8 range. Cooling issues resolved. Hope this helps. Jay B
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