Should my radiator return be cool at the onset of 200F water temp? - LotusTalk - The Lotus Cars Community
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post #1 of 10 (permalink) Old 07-12-2019, 07:38 PM Thread Starter
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Should my radiator return be cool at the onset of 200F water temp?

The thermostat in my 2005 Elise failed and the engine was very slow to reach running temp - the usual o-ring jam failure. I replaced it early this year with the Duralast 15078. Refilled the coolant with the Airlift. Everything seems fine. But now in the Texas summer I'm worried that I'm running too hot. The water temp reaches 197 or so within 8-10 min. Sitting at idle or in stop-and-go traffic in the hot sun (with AC) I get 208-214F. 200+ is common in normal city driving, with or without AC. I have the BOE tune so the fans are running on high at 196+. So tonight I put the rear on the ramps and went through the bleeding process, pretty much making a mess as coolant was oozing right away. One thing I noticed is that as the car ramped up to 200F, the inlet side of the radiator was starting to warm up but the discharge side was still cool to the touch. Is this low of flow through the radiator normal? Seems little odd to be running the fans on high if there ain't much heat to reject, but maybe that's pre-emptive. The heater was certainly blowing hot. Another complicating factor is this is the first summer I'm running without oil coolers, after doing the BOE cam to replace my wiped OEM cam. Maybe all this is normal, but I'm a little suspicious that there isn't enough coolant flowing through the radiator. Any perspectives welcome!
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post #2 of 10 (permalink) Old 07-12-2019, 10:00 PM
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Warm inlet hose; cool out = classic symptom of stuck closed thermostat.

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post #3 of 10 (permalink) Old 07-13-2019, 06:02 AM Thread Starter
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Yea this is my fear and I didn't test the damn thing before installing it. I'm going to do a bit of driving an measure the radiator tank surface temps.
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post #4 of 10 (permalink) Old 07-13-2019, 06:55 AM Thread Starter
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Drove around for a bit in the neighborhood, stopping to measure radiator tank surface temps. Even after 10 min of driving at 195-200, the radiator inlet tank reached 160 and outlet 120. Air off the inlet side is a bit warm and off the outlet side cool. This can't be right. I'm convinced at this point that I'm not getting enough flow through the radiator. There's a little bit, but it doesn't ever ramp up. Next task will be to pull the thermostat and test it. Maybe it suffered an early life failure.
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post #5 of 10 (permalink) Old 07-13-2019, 07:25 AM
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Wait.......

If you filled with the airlift, I would recommend draining and manually re-filling the coolant system BEFORE messing with the thermostat again. Search this site for lots of good tips on properly filling and bleeding the coolant system.....it's a pain on these cars. I dealt with the same issue and it was actually an air pocket in the return hose right before the thermostat.

A super cool and helpful member on this forum sent me these instructions and it solved my issue.

Bleed burp process - try this...

Fill the overflow coolant tank to the top. Really. All the way to the top when it is cold for 24 hours. Next, start the car and let it idle for 15 minutes. Don't drive it - just start it and let it idle with the heat circuit on. Watch the engine temps.. If it climbs up to 210+ rapidly - you have an air bubble...

Next if it doesn't go over 210 - shut it down and let it sit. If it's OK, it will purge the air. When it does, the tank will drain to about half way and it will be needing a refill. Do that - and repeat the process

If it is stuck with an air bubble (usually by the T'stadt or water pump), you'll need to squeeze the water hoses into the T'stadt from the lower right rear to force it into the T'stadt / water pump.
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post #6 of 10 (permalink) Old 07-14-2019, 03:23 PM Thread Starter
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Thanks. I'll get the car up on the lift, do some measurements, and then some hose squeezing and bleeding to try and break free an air bubble if that's what is really going on here. I'm not getting to 210 until its 95+ and I'm in traffic. Some coolant is definitely flowing.
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post #7 of 10 (permalink) Old 07-15-2019, 07:20 AM
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I figured out the procedure ArizonaExige details myself when I had to refill the cooling system after installing a water-to-oil cooler. The system is prone to an air lock around the thermostat.

Burping the hose in the engine compartment at the bleed screw helps, but what finally fixed it was getting the thermostat to open. With only air around it, you have to wait for it to heat soak without frying the engine (because there isn't enough coolant flow). The good news is that at idle everything happens slowly, so you have time to shut it off when the gauge gets too high (I turned mine off at 205 F), wait for the temperature to come back down, and then restart it again.
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post #8 of 10 (permalink) Old 07-27-2019, 07:52 PM Thread Starter
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170F Thermostat fixed the problem

Bottom line is that I believe you should run a 170F motorad thermostat when using the BOE tune. I tested two of the 180F motorad thermostats and they are barely cracked at 190F and were not fully open until ~205F. What I think happens with the motorad 180F + BOE tune is a steady state condition where the engine temp is close to 200F, the fans are running on high and a small amount of water is flowing through the radiator with a high delta T. The 170F thermostat seems to be the sweet spot, being fully open well before the radiator fans are kicked on high. I did a long drive today at 90F ambient and the engine ran between 185-192F. Nice to have this solved. I guess its also possible that I had some air in my previous install but I did two full cycles with bleeding and aggressive hose fondling to no effect before deciding to try the 170F thermostat.
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post #9 of 10 (permalink) Old 07-28-2019, 05:01 AM
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Forgive my ignorance but what is BOE tune?
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post #10 of 10 (permalink) Old 07-28-2019, 06:54 AM Thread Starter
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Quote:
Originally Posted by Flemgunner View Post
Forgive my ignorance but what is BOE tune?
The "Torque 200" tune from BOE Fabrication: https://www.boefab.com/products/boe-torque-200-na-tune
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