V8 Overheating issue / Fan problem - LotusTalk - The Lotus Cars Community
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post #1 of 19 (permalink) Old 06-18-2019, 07:29 AM Thread Starter
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V8 Overheating issue / Fan problem

My car is currently at the dealership for various repairs and maintenance. One thing that needed to be addressed was it started overheating the day before I was to take the car in. The technician says that the fans aren't coming on under normal conditions. He says that if the A/C is on then they will come on and the engine will not overheat. But if no AC or the heater is on then the car's fans will not kick on.

Any ideas?
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post #2 of 19 (permalink) Old 06-18-2019, 08:33 AM
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When the A/C is on it overrides the temperature setting that would turn the fans on and off. The logical route would be to figure out why the ECU is not controlling the relay to start and stop the fans under the control of the temperature. Does your temperature gauge work? Is all of the air bled out of the motor? Make sure the header tank is full and the overflow bottle is at the full cold mark when cold.
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post #3 of 19 (permalink) Old 06-19-2019, 04:41 PM
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According to the Lotus service notes there are 2 coolant temperature sensors. One for the temperature gage and one for the ECU. The ECU temperature sensor controls the fans. As David said the A/C switch overrides the ECU temperature setting. If the ECU sensor is bad it should turn on the check engine light. This is easy to test using a scan tool and look at the coolant temperature data. The ECU and the AC switch use the same fan relay so I don’t think that is the problem .

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post #4 of 19 (permalink) Old 06-23-2019, 01:29 PM
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Like it's been said before, the ECU turns on the fans when the AC is off and coolant temp above 100*C.

Scan the car with proper diagnostic software. See what temp the ECU is reading, compare that to actual temp. That should tell if the temp sensor is good or not. If sensor is good, command the ECU to turn ON the fans. If fans come on, you are overheating for other reasons. If not, further troubleshooting needed.

Also, overheating a V8 almost guarantees liner sealant issue in the near future. It'll show up as mysterious coolant loss, confirmed by an oil analysis test.

'03.5 Final Edition Esprit ~ 5.7lbs/hp; mildly modded - 430rwhp, 353rwtq
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post #5 of 19 (permalink) Old 06-23-2019, 07:08 PM
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Or ship the car to gmendoza’s shop and call it a day.
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post #6 of 19 (permalink) Old 06-25-2019, 04:01 AM Thread Starter
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Got a call from the technician. I believe he felt a bit sheepish when he admitted it was simply trapped air in the system. Looks like all is well again. Thanks for the help.
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post #7 of 19 (permalink) Old 06-25-2019, 06:42 AM
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If that is the problem you must keep a close eye on the level, you may have a leak and will have this problem again if it is not fixed. Make sure the header tank is full when cold and the overflow tank in the R/R wheel well is at the full cold mark when cold. If the level goes down, it is leaking out somewhere. Make sure the level switch in the header tank is clean and working so you get some warning.
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post #8 of 19 (permalink) Old 06-25-2019, 10:07 AM
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Before you panic after reading David's advice, remember that anytime you open and drain the cooling system, you should monitor the level in both the overflow bottle and the header tank. Expect the cold level to drop and need topping up, over the next 5 - 10 driving cycles. It should stabilize after that.

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post #9 of 19 (permalink) Old 06-25-2019, 06:45 PM
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It can take a few driving cycles to expel all of the air. That said, if the level keeps dropping you have a leak. If you don't see it on the floor that can be bad news. An internal leak can be expensive to fix. An external leak is going to be a lot cheaper and easier to fix like a loose hose clamp so start looking. If you have a pressure tester or can borrow one (Auto Zone lends them out) it can help find the leak. If you notice your oil level is rising that would not be a good sign. You can also have the coolant tested for combustion gases. If you test positive you blew a head gasket. Was the motor ever overheated?
David Teitelbaum
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post #10 of 19 (permalink) Old 06-29-2019, 08:33 AM Thread Starter
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Thank you both for the advice. I'm kinda thinking I may have a leak (external). I seem to remember seeing slight signs of escaping coolant on a hose and hose clamp while under the car a few months back. There's no way it could be classified as severe by any stretch of the imagination. But then again, I guess there shouldn't have been any sign of escaping coolant. And the coolant reservoir behind the passenger side wheel is perpetually empty. I'll dive underneath today and see if I can hopefully locate that spot again.
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post #11 of 19 (permalink) Old 06-29-2019, 09:51 AM
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Even a tiny leak will eventually cause enough loss of coolant for the motor to overheat. After enough driving cycles the level will get low enough and enough air will get in to prevent the water pump from circulating coolant. Once the water pump gets air in it you are "done". You should have gotten a warning from the low level sensor in the header tank. Clean the tank and make sure the sensor and warning light work. Keep a closer check on the coolant level in the header tank AND the overflow bottle. Find and fix all of the external leaks you can. If the coolant is over 5 years old drain flush and replace it with fresh stuff. The additive package (which includes a leak sealer) wears out. So even if you still have enough concentration of Ethylene Glycol to prevent freezing or boiling, the additive package is gone. The coolant can also turn corrosive (part of the additive package includes buffers to maintain the proper ph) and attack the metals in the cooling system causing corrosion and leaks. Use 50/50 soft water and a nationally branded permanent type anti-freeze like the good old green stuff, Prestone. The coolant should be checked annually for concentration and ph. As an owner check you should be checking the coolant level at least once a month along with tire pressure and oil level.
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post #12 of 19 (permalink) Old 07-03-2019, 09:28 AM Thread Starter
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I bought a coolant pressure tester and located the leak. I have since topped everything off and took the car for 2 spirited runs and had to top the system off twice. A decent amount after the first run and a somewhat less after the second. After reading jrealty's last post on cycles, I'm gonna hope this is normal. I did, however, test the cap with the pressure tester and it wouldn't hold a pressure past like 17lbs. So I bought a new cap rated at 21-25 lbs and it held even less pressure. Is the 21 lb. documented system pressure amount legit?
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post #13 of 19 (permalink) Old 07-03-2019, 04:14 PM
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The V8 is rated for a cooling pressure of 21 lbs? Wow, the 4s only run 15 PSI (one BAR).

First make sure that the cap you are running has two seals, one on the spring-loaded center section, and one larger one inside the top of the cap. Some Lotus 'genuine parts' don't have the larger seal these days, and you NEED that. I ended up buying a dusty old cap from an auto parts store...

Another watchpoint is the plastic header tank in the engine bay...they can develop stress cracks about an inch below the neck and no longer contain pressure. (I believe JAE can sell you new ones, they are from a Peugeot).

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post #14 of 19 (permalink) Old 07-04-2019, 08:00 AM
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Do not use a cap rated for more pressure than 17 lbs. Hard to test a new cap properly because the rubber seals are dry and cold. Even if the cap leaks a bit, it goes into the overflow bottle and should get drawn back into the system so the level should not go down, ie, you don't lose (leak) coolant. You do need to pressurize the system to raise the boiling point of the coolant but if you go above 17 lbs you will blow hoses and the water pump seal. The rad can also blow. Continue with your regime and you should notice that you will be adding less and less until it finally stabilizes. Be sure to ONLY add 50/50 soft water and anti-freeze. Test the low level switch in the header tank.
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post #15 of 19 (permalink) Old 07-04-2019, 09:24 AM
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Quote:
Originally Posted by jtrealty View Post
Do not use a cap rated for more pressure than 17 lbs. Hard to test a new cap properly because the rubber seals are dry and cold. Even if the cap leaks a bit, it goes into the overflow bottle and should get drawn back into the system so the level should not go down, ie, you don't lose (leak) coolant. You do need to pressurize the system to raise the boiling point of the coolant but if you go above 17 lbs you will blow hoses and the water pump seal. The rad can also blow. Continue with your regime and you should notice that you will be adding less and less until it finally stabilizes. Be sure to ONLY add 50/50 soft water and anti-freeze. Test the low level switch in the header tank.
David Teitelbaum

The V8 cap is rated a 145kpa, or about 20psi.

'03.5 Final Edition Esprit ~ 5.7lbs/hp; mildly modded - 430rwhp, 353rwtq
'65 Karmann Ghia, '80 930, '89 928 S4, '92 Corrado, '02 Maserati Coupe, '06 Murcielago
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post #16 of 19 (permalink) Old 07-04-2019, 10:02 AM
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Looking it up in the Technical Data section TDK V-8 engine page 6 Cooling System the pressure cap is supposed to be 15 lbs/in (110KPa). Increasing it 125% to 20 psi is a LOT.
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post #17 of 19 (permalink) Old 07-04-2019, 10:07 AM
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Quote:
Originally Posted by jtrealty View Post
Looking it up in the Technical Data section TDK V-8 engine page 6 Cooling System the pressure cap is supposed to be 15 lbs/in (110KPa). Increasing it 125% to 20 psi is a LOT.
David Teitelbaum
That, along with many others, is an error.

'03.5 Final Edition Esprit ~ 5.7lbs/hp; mildly modded - 430rwhp, 353rwtq
'65 Karmann Ghia, '80 930, '89 928 S4, '92 Corrado, '02 Maserati Coupe, '06 Murcielago
www.fquick.com/gmendoza
https://www.youtube.com/channel/UCPI...bwPaEI4JFbyCrA
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post #18 of 19 (permalink) Old 07-04-2019, 10:10 AM
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Quote:
Originally Posted by jtrealty View Post
Looking it up in the Technical Data section TDK V-8 engine page 6 Cooling System the pressure cap is supposed to be 15 lbs/in (110KPa). Increasing it 125% to 20 psi is a LOT.
David Teitelbaum
Looks like you've been down this road before.
https://www.lotustalk.com/forums/f16...4/#post3107290

'03.5 Final Edition Esprit ~ 5.7lbs/hp; mildly modded - 430rwhp, 353rwtq
'65 Karmann Ghia, '80 930, '89 928 S4, '92 Corrado, '02 Maserati Coupe, '06 Murcielago
www.fquick.com/gmendoza
https://www.youtube.com/channel/UCPI...bwPaEI4JFbyCrA
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post #19 of 19 (permalink) Old 07-04-2019, 11:49 AM
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Yes, it looks like this is history repeating itself again. I guess we are back to the V-8's being at 21 psi. That IS a lot and even a minor leak that would not have leaked at 15 psi will be a problem.
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