Cold lower hose

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stag888

stag888

Active Member
Posts
113
Location
Bromley , Kent
Hi
My Series 3 has started to running hotter , used to run dead centre , now pushing up close to the red . started to check a few things
  • Checked previous posts for some guidance
  • Replaced thermostat , did test old one , and it certainly didn’t open as much as new one
  • Checked rad , disconnected bottom hose , used the garden hose and water flowed straight through, that seems fine
  • Heater works , hot water makes it through heater pipes in & out & it blows as warm as used to
  • However the bottom hose remains dead cold , I run it for 15/20 minutes , temp goes up & whilst top is hot , it’s that that bothers me, and makes me question flow
Starting to think the water pump may be u/s , but before I go out and change that I’m keen to check I haven’t overlooked anything obvious .
Any guidance much appreciated
Cheers Steve
 
Fan belt tight/good ? even if spinning were it loose or very worn it this can result in it slipping and not pumping properly.
 
With the rad cap off and engine up to temp you can normally see the flow coming into radiator if series type.
 
Hi
OK thanks I'll give that a go tonight, I suppose that's exactly what I was asking how can I telI I have circulation. I have a sinking feeling that there is little flow or movement . I was also thinking of disconnecting the fan belt just to check the pump , although it's not leaking was keen to see if there is any play, noise or friction , plus also planning to carefully disconnecting the heater return pipe whilst running to see if I had flow / pressure .
Found the attached which helped my thought process


car-engine-cooling-system-diagram-prestone-release-imagine-so-630-427.png
 
Well checked water pump , no wobble, spins relatively smoothly , checked rad with cap off and yes the water does move , and increases in line with revs , doesn't seem like a huge amount , but then not sure how much the pump is expected to displace , so it is working . Temp still goes up to close to the red after 15/ 20 minutes of idle , and bottom hose still cold . I think next thing on the cheap check list will be the temp sender , and once I've got a replacement battery for my temp gauge I'll check the block temp .
 
For getting the bottom hose warm I think you need to take it for drive, just running for 15/20 min's is not enough, could be temp sender playing up or voltage regulator. Is the fuel gauge behaving?
 
I should get the temp sender in at the weekend , and can take it for a longer run then , let’s see what does .... fuel gauge seems to be behaving , so perhaps not voltage regular . Will see the weekend brings before I start thinking head gasket
Cheers
 
Hi Stag88. Having the exact same experience. Have replaced water pump, reverse flushed rad, new hoses and flushed matrix. Block test all good, which i am relieved about as i spent 2022 replacing it. Replaced dash voltage stabiliser and rad sender. Still running dashboard gauge near the red and bottom hose stone cold. Where did you get to? I am starting to think rad is blocked and should be replaced. Many thanks
 
Last edited:
Stag88 last seen in 22, when you flushed rad did water come out as quick as going in, if so unlikely blocked have you checked the thermostat is opening in hot water
 
steve2286w said:
Stag88 last seen in 22, when you flushed rad did water come out as quick as going in, if so unlikely blocked have you checked the thermostat is opening in hot water
Click to expand...
Many thanks for the reply. New thermostat installed and checked woth the kettle test. To be fair the old one was only 1 year old. Yes, rad gushes out of the bottom. Block test all good tonight, so relieved. Purged air out by loosening matrix hose and topping up. Flummoxed. Perhaps the gauge is shot, yet in 20 years and 5 series never gad a gauge fail.
 
I'd be more inclined to say gauge/sensor/wiring than anything else.
Top hose will get hot even before the thermostat is open, so the bottom may be cold simply because there is no flow. It may also be that it's only just hot enough to open the stat on and off, so by the time the coolant passes through the rad it's cooled sufficiently.
 
All series gauge's are getting well old. The one in mine just about lifts off the bottom when up to temp.
Check what temp you actually have with a IR temp reader, aim at thermostat, top hose, rad bottom hose.
I had a job to find a new thermostat for my Ninety last year, first replacement did not work at all, second packed up after a month. I then sourced a new in the box old stock Waxstat thermostat, all good since. There are some rubbish parts out there.
 
If the top hose is hot then the thermostat is opening or stuck open.
Remove the radiator cap. Rev the engine a bit, can you see the water move? If so then the pump is working. If the level doesn't rise then the water must be going somewhere ie through the radiator and back into the engine.
Measure the temp of the top hose, or the coolant in the top of the radiator
 
Many thanks both. I have just ordered an IR temp reader from off ebay as I am starting to think its actually fine on temp, but it is the sensor/wiring/new thermostat. Going to remove the termostat tonight and run it without it. I read last night that there is an old school trick to drill 4mm holes in it to increase initial cooling (although downside is less hot air for wind screen de-icing). Thanks again. I appreciate it. Once I get to a conclusion I will follow up to close this thread out in the event these symptons help someone else. I noticed how many dont - which I thought was this forums purpose in part. Debate, discuss, have a blokey banter laugh, yet ultimately technically help each other. Once again, thank you both in taking the trouble to respond. Its appreciated.
 
ORJIP said:
Many thanks both. I have just ordered an IR temp reader from off ebay as I am starting to think its actually fine on temp, but it is the sensor/wiring/new thermostat. Going to remove the termostat tonight and run it without it. I read last night that there is an old school trick to drill 4mm holes in it to increase initial cooling (although downside is less hot air for wind screen de-icing). Thanks again. I appreciate it. Once I get to a conclusion I will follow up to close this thread out in the event these symptons help someone else. I noticed how many dont - which I thought was this forums purpose in part. Debate, discuss, have a blokey banter laugh, yet ultimately technically help each other. Once again, thank you both in taking the trouble to respond. Its appreciated.
Click to expand...
Drilling the thermostat just means it takes longer to warm up which increases engine wear. It will have no impact on coolant flow once the thermostat is open.
Same goes for removing the thermostat, it just increases the time to reach running temp, if it ever does
 
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