Fluctuating coolant temp. M20B25

[Kepes 231]

Well then, time for an update! There's good news and there's bad news, let's start with the good

She's got a brand new radiator in her! as well as new rad hoses and expansion tank cap. It's amazing how much nicer the engine bay looks with the new radiator and crack-less hoses.

And the bad news - same problem!!! Not sure what's going on. The temp gauge never fluctuated before the head gasket was done. The head was resurfaced.
Seeing as this wasn't happening before the hg was done, I don't see a cracked head/block being an issue. The head was pressure tested, the block was closely inspected.

I thought for sure the new radiator would fix the problem as a week after I ordered it, the old radiator sprung a leak (thankfully doing most of the leaking while parked). I returned to my car one night and the check coolant light came on. Coolant all over the road. Filled the reservoir and drove home with my eyes fixed on the gauge. Got home sweet and didn't drive her until today when I installed the rad. I think the (very) little coolant loss I had in the past was from the radiator leaking.

So, not sure where to next
Draining all of the coolant every time I want to inspect/change something is annoying

I'll test the thermostat (only 2 years old) as per the instructions in the bentley manual
If that passes the test then I'll be installing a new water pump (1 year old)

So, that's my course of action but I welcome all opinions of what I should do!

Edited November 22, 2015 by Kepes

[_ethrty-Andy_ 2122]

you have checked the temperature sender itself is in spec right? how about the gauge?

[polley 916]

Don't think they fit backwards.

[e30ftw 393]

Thermostat in backwards preventing flow - or something else - but as Alan said many posts ago - FLOW is your problem get professional advice

But we are the professionals.

[polley 916]

Get it scanned.

[Kepes 231]

you have checked the temperature sender itself is in spec right? how about the gauge?

I checked the gauge - all good. I don't know how to check the sending unit (brown sensor). It has 1 prong and there is no explanation in the bentley manual on how to do it/what the resistance should be at x degrees Celsius.

Thermostat in backwards preventing flow - or something else - but as Alan said many posts ago - FLOW is your problem get professional advice

If it is flow then the only related things changed during the hg were water pump, and I did take apart the thermostat housing. I really do think that it was something that changed during the process because the problem began as soon as it was back together.

The fan has some horizontal movement to it aka it wobbles a tad.

A couple of months back I parked my car up the ski field (below freezing temps) for the weekend. When I started it, there was a whining noise from the front of the engine (wp bearing!?) which went away by the time I opened the bonnet. I can't really explain the sound. Kinda like a fuel pump that's about to go bad.

I'm really leaning towards a faulty waterpump.

The Bentley manual lists advanced timing as a probably cause of overheating. It was my first time doing a timing belt, and although the marks looked good to me, the car pings on 91 and even 95 under load. I didn't think much of it and just used 98 fuel, problem solved masked. I thought that the resurfacing of the head was the reason for it.

Could the timing marks being off by a few degrees be the issue?

But we are the professionals.

Right! I really enjoy working on this car and the problem solving side to it. I'll get there in the end.

Edited November 23, 2015 by Kepes

[hotwire 352]

With respect Toby - you really are stabbing in the dark here.

Will gave comprehensive testing procedures a few posts back.

Off the top of my head:

Water pump - unlikely

Thermostat - maybe

Air lock since refilling - maybe

Cam timing - maybe

Ign timing - maybe

Crack - block/head - maybe

Head gasket - maybe

You cannot assume there are no issues with what has been done. It requires systematic diagnosis of all possibilities.

I realize you are on a budget but if you don't have the resources to diagnose/fix, it might be a lot simpler to get it professionally checked. It will not be a major to diagnose

Edit - how do you know the gauge is working correctly? the fact it goes from cold to hot by earthing/insulating the wire does not mean correct operation.

What is the actual temperature?

Also - is it still using water?

Edited November 23, 2015 by hotwire

[Kepes 231]

With respect Toby - you really are stabbing in the dark here.

Will gave comprehensive testing procedures a few posts back.

Off the top of my head:

Water pump - unlikely

Thermostat - maybe

Air lock since refilling - maybe

Cam timing - maybe

Ign timing - maybe

Crack - block/head - maybe

Head gasket - maybe

You cannot assume there are no issues with what has been done. It requires systematic diagnosis of all possibilities.

I realize you are on a budget but if you don't have the resources to diagnose/fix, it might be a lot simpler to get it professionally checked. It will not be a major to diagnose

Edit - how do you know the gauge is working correctly? the fact it goes from cold to hot by earthing/insulating the wire does not mean correct operation.

What is the actual temperature?

Also - is it still using water?

No offence taken! I appreciate you're response, you know what you're talking about. I am stabbing in the dark.

You're probably right in that I should get a mechanic who knows what they're doing to diagnose the problem.

Yes that's exactly what I did to test the gauge as per the instructions in the Bentley manual, what else can be done to test the gauge correctly?

The gauge is behaving extremely consistently, with the needle rising in the situations mentioned.

I've only had the radiator in for 1 day. No coolant loss yet however I will keep checking it.

The upper radiator hose is higher than the bleed screw, so potentially air still in the system. It is self bleeding over time (so I hear) so I'll give it a week or so.

Thanks for your help again Grant.

[hotwire 352]

Gauge check - that is merely telling you the gauge is operating to extremes - not that the temperature it is displaying is correct.

I would be wanting to monitor actual temperatures at engine/radiator etc in relation to the to gauge readings & its variations.

Did you have the heater on hot (tap open) when filling & bleeding? M20's can be a bitch to bleed for the unsuspecting.

What I finds works - heater control to hot, bleed screw open, approx 2/3 fill the system, run engine up to temp (thermostat open) then gradually top up & shut off bleed screw once air stops. It can normally be bled in one hit. Recheck level when cold.

If the heater was not open when you filled the system - i would highly suspect an airlock.

[_ethrty-Andy_ 2122]

dont know why people always say BMWs are a bitch to bleed. I have done dozens of coolant changes on all manner of engines and bodys, never had a problem. heater on, bleed screw open and fill her up.

i most likely have a brown top sensor here you can try, or get one off Elijah his M30 should be the same sensor from memory although his engine got a little toasty at some point too, but thats another fault.

only a 10 minute tear down to check the timing on a facelift engine, havent done it on a prefacelift but cant imagine there is much more if any more to doing it.

Id love to say come round and we'll spend an afternoon on it but im flat out at the moment on my own cars and also renoing the house too.

[Kepes 231]

Gauge check - that is merely telling you the gauge is operating to extremes - not that the temperature it is displaying is correct.

I would be wanting to monitor actual temperatures at engine/radiator etc in relation to the to gauge readings & its variations.

Did you have the heater on hot (tap open) when filling & bleeding? M20's can be a bitch to bleed for the unsuspecting.

What I finds works - heater control to hot, bleed screw open, approx 2/3 fill the system, run engine up to temp (thermostat open) then gradually top up & shut off bleed screw once air stops. It can normally be bled in one hit. Recheck level when cold.

If the heater was not open when you filled the system - i would highly suspect an airlock.

Right, middle of the gauge is about 90 degrees isn't it? I'll try get one of those infra red temp readers.

Yeah, heater was on/open.

I've drained the cooling system so many times and usually without any issue so it probably won't be an air lock, I guess I just said it was to give myself some false hope or something

I think what you alluded to is probably the best option - get a mechanic who know's what he's doing to check it out

[Kepes 231]

dont know why people always say BMWs are a bitch to bleed. I have done dozens of coolant changes on all manner of engines and bodys, never had a problem. heater on, bleed screw open and fill her up.

i most likely have a brown top sensor here you can try, or get one off Elijah his M30 should be the same sensor from memory although his engine got a little toasty at some point too, but thats another fault.

only a 10 minute tear down to check the timing on a facelift engine, havent done it on a prefacelift but cant imagine there is much more if any more to doing it.

Id love to say come round and we'll spend an afternoon on it but im flat out at the moment on my own cars and also renoing the house too.

I feel the same way as you, I've never actually had a problem bleeding it. I'll start by checking the temps and comparing them to what the gauge is telling me.

That would be cool, but I'm working weekends atm so looks like we both have our hands full! Good luck with the reno

[_ethrty-Andy_ 2122]

Good luck with the reno

Thanks mate, clean sailing thus far, no real surprises... surprising for an 87 year old house

[Kepes 231]

Thanks mate, clean sailing thus far, no real surprises... surprising for an 87 year old house

If only cars held up just as well

[Kepes 231]

Got frustrated and pulled the skid tray and lip etc to have a good look after work.

Looks pretty obvious that I have a leak from the weep hole on the water pump. It is also making some bearing noise.

[hotwire 352]

Well that is crap for the age of it. That said, the new GMB unit I fitted to my E39 lasted a week before leaking It had replaced the original that had done 150k before collapsing its bearing. Needless to say - I was NOT impressed!

[Kepes 231]

Well that is crap for the age of it. That said, the new GMB unit I fitted to my E39 lasted a week before leaking It had replaced the original that had done 150k before collapsing its bearing. Needless to say - I was NOT impressed!

I know exactly how you feel! I'm also angry at myself for not properly diagnosing it before buying the new radiator. Oh well, Now I've got two good radiators.

It was dark when all of my coolant leaked on the street. Parked on a very steep hill, obviously it caused the coolant to come out the weep hole on the slope. I just assumed it was the radiator.

I was actually going to order a GMB unit as this one was an OEM Saleri unit, but I may reconsider after hearing your experience.

Edited November 25, 2015 by Kepes

[hotwire 352]

Dare I say - i did suggest you get the radiator checked by a radiator shop.

I have used plenty of GMB units at work over the years without issue.

When I found my E39 unit had failed on a Sunday arvo, & not having pre organised an OEM replacement, i went to Repco, had the choice of a Repco branded Chinese unit or a GMB at about $10 dearer. Closer inspection confirmed the Japanese GMB unit was too made in China

Logic told me though - the GMB unit should still be better. Famous last words!

[Kepes 231]

Yeah you did and now I wish I had listened

Went to Repco today and the sell the GMB unit for $102. It's $30US online and I need to buy a valve cover gasket anyway so looks like the E30 will be retiring until it arrives. Started to over heat on my way home from work today. I've become used to glancing at the temp gauge every now and then so I got the heater on full blast and made it home.
I've been incredibly lucky come to think of it

[hotwire 352]

Mine was much less than that but it was trade.

Must say though - in this case - not necessarily convinced your water pump is the overheat cause though, Yes on the later units where the plastic impellers split & then slip.

Cant say I have seen an M20 unit fail like that though. The leak will not cause this.

[Kepes 231]

Mine was much less than that but it was trade.

Must say though - in this case - not necessarily convinced your water pump is the overheat cause though, Yes on the later units where the plastic impellers split & then slip.

Cant say I have seen an M20 unit fail like that though. The leak will not cause this.

Apparently the leak represent coolant getting passed the internal seal? Or something like that. From what I've read, when the weep hole leaks it means there's coolant passing through the bearing and therefore it's on it's last legs if not already broken

[hotwire 352]

Yes true but that wont cause an overheat. Unless it has spat out all the coolant or the impeller is not turning & pumping water. Both unlikely on yours I would think.

[Kepes 231]

Yes true but that wont cause an overheat. Unless it has spat out all the coolant or the impeller is not turning & pumping water. Both unlikely on yours I would think.

You're more experienced than me so you'll know better, but given that there's a leak from the wp do you think it should be replaced?

[hotwire 352]

Yep absolutely! I just suspect there is another reason for the temp issue. Do the pump first though.

It is a matter of fixing the known issues first.

Reminds me of a certain V8 Falcon sitting in our workshop. Have bloody near rebuilt the car it seems - one thing leading to 10 more Has done 450k though. Hopefully will leave tomorrow & stay away for a while.

[Kepes 231]

Yep absolutely! I just suspect there is another reason for the temp issue. Do the pump first though.

It is a matter of fixing the known issues first.

Reminds me of a certain V8 Falcon sitting in our workshop. Have bloody near rebuilt the car it seems - one thing leading to 10 more Has done 450k though. Hopefully will leave tomorrow & stay away for a while.

Yeah it is extremely frustrating!!

Thanks heaps for all of your help Grant, I really appreciate it. I'll get the water pump done and report back

Edit: Are you a mechanic?

Edited November 25, 2015 by Kepes