Jump to content


Photo
- - - - -

Running Lean Causing Overheating?


  • Please log in to reply
30 replies to this topic

#1 Mike92

Mike92

    Previously known as PoweRMikE.

  • TMF+ Member
  • PipPipPipPipPip
  • 337 posts
  • Location: Plymouth
  • Local Club: South Devon Mini Club

Posted 06 April 2018 - 11:49 AM

Hi Guys,

 

I've been trying to figure out why the Mini (1989 998cc stage 1 kit fitted with a HS4 carburettor) has been running hot, primarily at higher speeds such as on the motorway. I've checked the temperature gauge which looks like it goes up to about 90-95 degrees. I've upgraded the radiator to an aluminium Fletcher rad in hope that it may help the issue, which has helped a bit, but not enough that it still runs quite hot at times. However, when sitting it traffic, idling the temperature sits bang on where it should be in the middle.

 

After looking at the past MOT emissions test, the CO reading is 0.56% and the limit is 3.5%. I've heard many stories of fellow Mini owners having to weaken their mixtures to pass the MOT check, is this a hint that the Mini may be running too lean, causing the overheating?

 

One other thing which may also be a hint that it's running to lean (or something else entirely!), which is whilst cruising and then applying full throttle it'll feel as if it holds back, then after around half a second it'll then accelerate as it should.

 

If anyone can shed some light on this it will be much appreciated! Many thanks



#2 nicklouse

nicklouse

    Crazy About Mini's

  • TMF+ Member
  • PipPipPipPipPipPipPipPipPipPip
  • 9,850 posts
  • Location: Not Yorkshire

Posted 06 April 2018 - 11:59 AM

what needle came with the stage 1 kit?

have you looked at the plugs to check if it is running lean?

#3 area51

area51

    Learner Driver

  • Noobies
  • PipPip
  • 20 posts
  • Location: Lancashire

Posted 06 April 2018 - 12:41 PM

Hi, check the timing, as if it is out it may cause the issue.
Also the water pump. Is it the original? After a while the impeller corrodes, thus the pump becomes very ineffective in pumping coolant round the engine.

#4 Mike92

Mike92

    Previously known as PoweRMikE.

  • TMF+ Member
  • PipPipPipPipPip
  • 337 posts
  • Location: Plymouth
  • Local Club: South Devon Mini Club

Posted 06 April 2018 - 12:51 PM

I believe it's running on a AAU needle. 

 

I've just checked the plugs, condition of them seem to vary, see the pictures below:

 

#4:

SparkPlug4.jpg

#3 (Not sure why this one is so black!):

SparkPlug3.jpg

#2:

19927a2d-6019-4d6d-95b2-f988a1e53270.jpg

#1:

2f5005f4-7b60-421e-aeef-6affe548f7d4.jpg

 

I'll have a look at the timing, I believe the water pump is original which could be the culprit! 



#5 dyshipfakta

dyshipfakta

    One Carb Or Two?

  • Members
  • PipPipPipPipPipPipPip
  • 1,377 posts

Posted 06 April 2018 - 12:57 PM

hmm that plug on 3 doesnt look good at all. Any misfiring? Does it pull well?

#6 Mike92

Mike92

    Previously known as PoweRMikE.

  • TMF+ Member
  • PipPipPipPipPip
  • 337 posts
  • Location: Plymouth
  • Local Club: South Devon Mini Club

Posted 06 April 2018 - 01:01 PM

Haven't noticed any misfiring as such, I think I'll give it a compression test and give the plugs a clean. I only recently changed the head gasket a couple months ago so I hope nothing major is going on!



#7 Rorf

Rorf

    Speeding Along Now

  • TMF+ Member
  • PipPipPipPipPip
  • 370 posts
  • Location: Cape Town

Posted 06 April 2018 - 01:19 PM

No 1 and 2 look excellent, No 3 is very oily and No 4 is very clean - a sign of a possible head gasket coolant leak on No 4. Also explains the increase in heat at higher road speeds.

 

Did you skim the head on the last head gasket change?



#8 Mike92

Mike92

    Previously known as PoweRMikE.

  • TMF+ Member
  • PipPipPipPipPip
  • 337 posts
  • Location: Plymouth
  • Local Club: South Devon Mini Club

Posted 06 April 2018 - 01:39 PM

Thanks for that Rorf, good to know. 

 

I didn't skim it last time no, however the head gasket change before this one I did get it skimmed (probably around a year ago now).



#9 nicklouse

nicklouse

    Crazy About Mini's

  • TMF+ Member
  • PipPipPipPipPipPipPipPipPipPip
  • 9,850 posts
  • Location: Not Yorkshire

Posted 06 April 2018 - 01:47 PM

I would get a compression test done.

#10 Mike92

Mike92

    Previously known as PoweRMikE.

  • TMF+ Member
  • PipPipPipPipPip
  • 337 posts
  • Location: Plymouth
  • Local Club: South Devon Mini Club

Posted 06 April 2018 - 02:06 PM

Yeah that's the plan for tomorrow me thinks! 

 

Thanks for all the help and suggestions so far guys



#11 Rorf

Rorf

    Speeding Along Now

  • TMF+ Member
  • PipPipPipPipPip
  • 370 posts
  • Location: Cape Town

Posted 07 April 2018 - 05:33 AM

If you remove the head have it pressure tested also to ensure there are no cracks especially between the inlet and exhaust valves of No 4



#12 Mike92

Mike92

    Previously known as PoweRMikE.

  • TMF+ Member
  • PipPipPipPipPip
  • 337 posts
  • Location: Plymouth
  • Local Club: South Devon Mini Club

Posted 07 April 2018 - 10:41 AM

Right I've just been out and did a compression test (engine warmed up prior) with the below results:

 

|   4   |   3   |   2   |   1   |

| 170 | 175 | 153 | 164 | (PSI)

 

Does that dip in PSI for #2 sound a bit low to you guys?

 

I think I'll grab a new water pump for it anyway seeming as it's the original still in there, it's no doubt probably seen better days


Edited by Mike92, 07 April 2018 - 10:44 AM.


#13 tb205gti

tb205gti

    Mini Mad

  • Members
  • PipPipPipPip
  • 169 posts
  • Location: Denmark

Posted 07 April 2018 - 01:37 PM

Hmm I have the exact same issue with mine. City driving and slow driving is OK - motorway and the gauge goes pretty high. It have never boiled though, and there are no signs of overheating apart from the gauge.

 

Running a 940 head with raised compression. Plugs looks fine, maybe a bit to the rich side.



#14 Rorf

Rorf

    Speeding Along Now

  • TMF+ Member
  • PipPipPipPipPip
  • 370 posts
  • Location: Cape Town

Posted 07 April 2018 - 03:53 PM

Those pressure readings are contrary to the plug numbers; are you numbering from the radiator side (No 1) :proud:

 

If you are not using a heater off take from the No 4 side then this side of the engine can run warmer then the pump side.

 

Good idea to replace the coolant pump, also give the block a good flush and ensure you use a good quality coolant.



#15 Ado1379

Ado1379

    Speeding Along Now

  • Members
  • PipPipPipPipPip
  • 489 posts
  • Location: Northern Ireland

Posted 07 April 2018 - 04:37 PM

I have had this problem, I even had a Gunson Colortune on each cylinder and I was getting the same results as indicated by your spark plugs.
It turned out to be my head gasket leaking (head is being skimmed on Monday)

What gave it away for me was the bubbles in the radiator as soon as the thermostat opened




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

Mini Spares