Bottom hose cold engine running hot v6
 

Hi just started using my car after flushing the cooling system along with a new genuine rover thermostat. Everything started off ok for the first hour running between 89-93 degrees on obd display then in traffic temp rose to 100-101 fan come on and cooled it back down to 95 degrees in about 1 minute it then dropped to 92 degrees. Then driving around town i noticed it started running between 96-99 degrees and when stuck in traffic fan came on at 100 initially rose to 102 then eventually dropped down to 96 after about 3-4 minute but wouldn't drop down to 95 to turn the fan off. When i got home i checked the top hose which was red hot however the bottom hose with the bleed screw in was cool i switched the engine off and for some reason the bottom hose got hot again. Iv noticed a slight coolant leak from where one of the rubber hoses goes on the metal rail pipe which goes to the oil cooler. I had to top up the coolant this morning by about a cup full there wasn't no pressure when i unscrewed the cap i changed the coolant last week.I think thermostat might be faulty even though its new.
Anyone any ideas thanks

How is the cabin heater, hot air or not, usually a good indicator of if there is air in the system.

Regards

Forgot to check that I'll start car up again to see if it gets hot. I had the heater on at first when temperatures were normal and it was red hot but I'll check it again.

The heater is hot i drove it agsin just now and the temperature was between 90-93 degrees however when i slowed right down it went upto 96 degrees, when i got home the bottom radiator pipe was still hot and the heater was still hot however the temperature never got to 100 degrees it was just staying at 99 degrees when i revved the engine temperature dropped to 93 degrees then quickly rose back to 99 degrees stayed there for 30 seconds then fan came on at 100 and cooled the engine back down to 95 in about a minute the heater was blowing hot and the bottom radiator pipe was still hot

Pete, three important points for you:

1. Your thermostat isn't faulty.
2. You need to stop the leak you've identified. It will prevent the cooling system pressurising properly and cause the variable temperatures you are experiencing.
3. Did you refill and bleed the system according to the MG Rover procedure? Crucially, did you refit the bleed screw before starting the engine and did you raise the expansion tank?

Simon

Yep i raised the tank until there was a short jet of coolant and left it raised whilst i tightened the bleedscrew, they was also a slight weep coming from the screw aswell but i tightened it a bit more and it stopped, if you try tightening anymore it goes tight then loose then tight again. I think I'll get an updated stainless steel pipe rail but it might just be the clip that joins the rubber hose onto the pipe.

Good that the heater is working and that the lower hose is now hot - sure as Simon points out leaks prevent pressurisation but I wouldn’t be surprised if there were still a few air bubbles hiding: we’ve got four 75s at home, two have been absolutely no problem to bleed, one took several test drives to fully bleed as we kept finding air coming out of the bleed screw, and the fourth was just about impossible, totally defeated the ex-Rover dealer garage despite months of effort, and allowed me to buy the car as “spares”. It sounds like you’ve almost cracked it but if you dare touch it, loosen the bleed screw while the engine is running - air or coolant ?

Regards

Thanks to both you and simon for your advice I'll give it a try forgot to say after the first run you could hear slight bubbling in the top hose after i turned the engine off.

That suggests a damaged thread on either the screw or hose. I'd suggest that you renew both.
I regret that I have to disagree fundamentally with this. The MG Rover bleeding procedure specifies that the screw should be tightened before starting the engine and not touched again. If it is suspected that some air remains in the system, it is because there is another problem. This must be identified and corrected. You have already identified it Pete; the leak mentioned earlier. Loosening the bleed screw is not the solution.

Simon

Don’t worry about it Simon, there will be times when we agree and obviously disagree. In the example above I mentioned two cases where I have found a non-MGR method works, and in my mind when a pressurised coolant system is opened one of two things come out of the bleed screw, either coolant or air.

When a professional ex-MGR dealer garage have tried all the conventional methods (with no other problems as they'd changed everything except the headgaskets which they were considering) over a period of several months and still get nowhere then I’m up for unconventional methods and I end up with a very cheap car with lots of new parts.

Mike