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QP M139 F1 engine heat issue (potential overheating)

6K views 36 replies 9 participants last post by  Jim bob 
#1 ·
Hi, first post. 2months of ownership of a M139 sport GT 2007

So when I got the car I did just drive for bit without really checking anything. The car seemed mech A1. I noticed when stopping for a while at times where I have been going slow, the overflow for the radiator bubbles and gurgles. That to me sounds like boil over. The thing is, the temp guage never goes over 90degC. I've never seen it go higher and I've never got a overheat warning etc.

I decided to give it a bit of a look over. The coolant seemed low so I followed the manual, set the climate control to max hot to open the heaters and filled to correct level. Did a long drive and some slow driving before stopping. When stopping coolant overflowed all over the ground. Since then, the coolant level has obviously gone down. The tempt gauge still doesn't go above 90degC and it gurgles when driving slow and stopping like it is overheating.

Two theories here - 1. blown head gasket. Probably should get the coolant system sniffed for combustion gases. 2. bad thermostat. Should just replace it anyhow.

Anyone seen this? It's almost like the gauge is broken or they purposely didn't allow it to go over 90degC so as not to scare the driver (seen jeep do this with oil pressure because of complaints). That is jeep showed a fake oil pressure so drivers didn't get worried at idle! It's odd that it boils but temp gauge is not high.

thanks.
 
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#4 ·
Hey guys, thanks for the responses. Ok so there is definitely a problem. I'll need to keep sorting this.

I decided not to top up coolant and see what happens. Gauge stays 90degC, I stop and the coolant system is aggressively whistling out the overflow. Clearly overheating so I'd say the gauge is not telling the truth.

I'm still 90% this is a blown head gasket and a stuffed temp sender. Don't always get white smoke with a blown gasket. I can't see what else would cause this. If anyone has come across this, would love to hear it. No warnings from the car, gauge on 90degC, car overheating.

Thanks.
 
#6 ·
Generally what happens these days is that the heads will be warped...Most everything is using full out stainless steel head gaskets so they are hard to blow...You can use a fluid test to check for that or a gas analyzer if you have access to one...Jason
 
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#8 ·
Could it be a case where the cooling system simply isn't holding pressure, thereby allowing coolant to boil? In the old days when a radiator cap failed, you would boil coolant out the overflow tube, but not because of overheating, but because the system wasn't holding the correct pressure. Could the overflow tank cap be bad?
 
#9 ·
12 cylinders I like this idea. Yes quite possibly the lid is buggered.

If the F136 uses steel gaskets I agree that it's unlikely to be a blown headgasket.

I think I will do the following,

Test the sender and gauge by heating the sender in boiling water and see if I get the correct reading over 90degC on the gauge

Pressure test the lid

If all seems ok I will pressure test the entire coolant system.

I put more coolant in today and it sat on a nice 87degC while cruising home at 80klm/hr.
 
#11 ·
Well... It's definitely really hot tonight. Check my vid out below. I've another theory. Faulty temp sender is giving false gauge reading and false signal to ecu to turn on fan? Does the same sender do both?
I'll have to fix this before I go too far I think.

 
#15 ·
So I've confirmed something today. Definitely gauge is not reporting true temp and fans not coming on. Running aircon puts a fan on and keeps temps much lower but not quite enough to stop a boil over. I'm 90% this is a dodgy sender causing fans to not come on
 
#16 ·
You can get a thermometer to put into the reservoir. Use that and a obd scan tool (basic one is fine) to compare what the thermometer and the scan tool are showing for temperature. That’ll tell you right away if it’s a sensor issue or something else.


Sent from my iPhone using Tapatalk
 
#17 ·
The sensor is a RTD. It changes resistance with temperature. Remove the connector and measure the resistance of the sensor on a cold engine. You can remove it put it in ice water and measure the resistance as it comes up to room temperature and then add it to hot water.
I have done this on another car that had cold start issue but at <-10C temperature. The sensor was still connected to the ECU but just in a container of water.
RTDs are pretty robust but it could be connection to ecu or a pocket of air at the sensor.
 
#18 ·
Hi, first post. 2months of ownership of a M139 sport GT 2007

So when I got the car I did just drive for bit without really checking anything. The car seemed mech A1. I noticed when stopping for a while at times where I have been going slow, the overflow for the radiator bubbles and gurgles. That to me sounds like boil over. The thing is, the temp guage never goes over 90degC. I've never seen it go higher and I've never got a overheat warning etc.

I decided to give it a bit of a look over. The coolant seemed low so I followed the manual, set the climate control to max hot to open the heaters and filled to correct level. Did a long drive and some slow driving before stopping. When stopping coolant overflowed all over the ground. Since then, the coolant level has obviously gone down. The tempt gauge still doesn't go above 90degC and it gurgles when driving slow and stopping like it is overheating.

Two theories here - 1. blown head gasket. Probably should get the coolant system sniffed for combustion gases. 2. bad thermostat. Should just replace it anyhow.

Anyone seen this? It's almost like the gauge is broken or they purposely didn't allow it to go over 90degC so as not to scare the driver (seen jeep do this with oil pressure because of complaints). That is jeep showed a fake oil pressure so drivers didn't get worried at idle! It's odd that it boils but temp gauge is not high.

thanks.
 
#19 ·
Hi, interesting reading... I have a 07 QP.( with later auto gearbox)
Hopefully it’s not a head gasket issue.. it might just be an air lock somewhere

Also, have you noticed if your radiator cooling fan comes on ?
I know mine does quite often...
Why not, drain the whole system and refill ..just to try.
Whatever... good luck with it.
 
#20 ·
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This is where I start to cringe hard and almost cry. It would appear that my driving around with the system building up pressure has started to cause failures of seals in all sorts of places. I've got a radiator tank leak as well but this one..... It appears the O-ring between the castings has failed. Only way I can see to fix this is to remove the entire front cover from the motor (the one the thermostat housing is bolted to). Can anyone confirm? No easy way to solve this? I'm having terrible luck with this car. Thanks.

Oh, so my thermos definitely not coming on unless I run air-con. 99% the temp sender is bad. I've ordered a new temp sender. Will also get a new thermostat.
 
#22 ·
Sir, what you have going on is a dumpster fire of diagnosing a broken automobile...You haven't figured out why the car is building excessive pressure, but want to figure a way to repair a coolant leak...Did you ever do a block test? I can only help people that want to follow a process...I'm 99% sure it isn't the coolant temp sensor BTW....Jason
 
#24 ·
I have some updates on the problems with my Maserati.

I removed the temp sender and replaced it with a 120ohm resistor. According to the datasheet this should be equivalent to around 117degC. I turn on the ignition and the temp gauge climbs to 90degC and stops. No overheat warning, no fans. Removing the resistor drops temp to 0degC confirming that the ecu is reading the resistor.

What could cause this? I'm at a loss and may have to visit the Maserati workshop.

Note: this supports my suspicions. The whole system is only reading to 90degC then it's just not registering anything hotter. I thought it was the sender but I've tested resistance vs temp. Sender follows datasheet

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#25 ·
What does the OBD reader show for the coolant temp (you don’t even need a fancy one as this is part of the standard/generic EOBD pids)? Ignore the temp gauge itself for now. Manufacturers often put dead bands to not freak customers out.

Do you have another 120 ohm resistor? Put it in parallel with that one (to get effectively 60 ohms). Does it change?

I suspect everything here is working fine and may be a red herring.

Sent from my iPhone using Tapatalk
 
#26 ·
Update:

Swapped out the resistor for potentiometer and did some playing. Interesting... Set pot to 50ohm. At first the gauge would only go to 90degC then it suddenly shot to max. Every time I first turned on the key the temp gauge was reluctant to rise but after that happened it now shoots straight to temp. So yes, dicky gauge.

The ecu is reading the temp correctly the whole time as tulit you said. Thanks for the tip on the obd too. Didn't know they were that simple.

Jason @ enzo's atlanta - you are right. Nothing wrong with the temp sender or ecu reading and looking more and more likely to be a gas in coolant issue. Block test tomorrow and will post results.

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#27 · (Edited)
Hi everyone. I was hoping to reply with this solved but I am once again reaching out for assistance because I'm really at a loss. Ok, where we are up to,


- Block test done - no apparent issues, great!

- thermostat test done - operates correct at correct temp

- Vacuum and pressure test entire coolant system (now good after a few fix ups).

- Coolant fans confirmed not coming on at all

- tested relays - all good. Properly tested, Yes they are good.

- relays bypassed (shorted) - fans come on. Also tested overall cooling system performance and it is A1 if I mimic the fan on/off manually by shorting. So this problem is cooling fans but no solution yet.

- checked main relay fuses - good

- checked in radiator resistor - faulty, bypassed for now (shorted). New one on order.

- result fans will NOT come on at any temperature

I see some spoke of a fuse in the cabin under the passenger well (USA) that was faulty and causing this. I logic tested every fuse in the car (under bonnet and under dash) with all coming up OK.

I then removed the cooling fan relays. Ran the car up to 95degC (ECU recorded temp via OBDII) and put a meter on the solenoid pins (86/89 I think). 3.5v constantly on both relays.

It's odd the 3.5v. Almost like a floating ground or something weird. So the relays are not getting a +12v to work as though the ECU is not sending signal. ECU temp reads ok. The only other experiment I ran was to unplug the thermostat mounted temp sender which threw a temp sender fault. The ECU went into fault mode, showed 100degC constant and the fans CAME ON. So fault mode sends a signal to the relays but normal mode does not.

Questions: What does the radiator mounted temperature sender do? I'm lost to it's purpose. I haven't tested it yet.

Questions: Does anyone have a wiring diagram for the cooling fan circuits?

Some photos/vids for your amusement below (yes the dust is making me sad too and I want to drive me car again)

Block Test Video HERE

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