Mi Running Hot

[Tom Fenton 1,548]

A bit ago I decided to neaten up the coolant plumbing on my Mi with some BBM hoses. It now looks much better but ever since doing so it runs hot on the gauge.

 

Here are two pics, old and new.

 

OLD

 

NEW

 

 

Any thoughts gratefully received, I will be putting the plumbing back to how it was unless anyone has any better ideas? The strange thing is that surely lots of others use the very good quality BBM hoses without any issue, so why has my car started to run hot since fitting them??

[Anthony 1,003]

My guess is that it's nothing to do with the hoses themselves - I like many others have run them for years and never had any issue - and rather something that's occured as a result of the hose fitting, such as there still being air trapped somewhere, thermostat sticking, or perhaps somehow you've partly blocked the rad by disturbing a load of sediment somewhere draining and refilling.

 

Is it always hot regardless, hot just under sustained load, or just hot in traffic/idling?

 

The new way that it's plumbed in should be fine, as that's how an 8v is as standard and clearly works just fine.

[welshpug 1,666]

I'm a bit baffled, looks like you havent changed anything at all bar where the heater return goes, which shouldnt affect it

[Miles 331 1 Cars]

Try ditching the rear water pipe, not needed in the 205

[Ryan 99]

I plumbed mine like your second pic and it's been fine for five years, so I doubt it's the slight change in layout.

 

How hot is "hot"?

[feb 47]

Excuse the probably daft question but which way does the coolant flow in the heater matrix pipes?

 

As I understand, on the top diagram, water flows from the green most left heater pipe to the thermostat, right? Then out of the thermostat and up to the heater to the right port?

 

The above assuming the thermostat is open. What about when the thermostat is closed?

 

With my (probably wrong) understanding I would think that with the new setup the engine would run cooler as water would alwayscirculate through the heater matrix (as opposed to before).

[dee205 3]

Excuse the probably daft question but which way does the coolant flow in the heater matrix pipes?

 

As I understand, on the top diagram, water flows from the green most left heater pipe to the thermostat, right? Then out of the thermostat and up to the heater to the right port?

 

The above assuming the thermostat is open. What about when the thermostat is closed?

 

With my (probably wrong) understanding I would think that with the new setup the engine would run cooler as water would alwayscirculate through the heater matrix (as opposed to before).

 

 

I could be wrong but I was under the impression that the water distribution block was the return or cooler ( for want of a better word ) with the real hot water leaving the engine via the thermostat when it opens at a certain level and then through the matrix and rad where it is cooler before being returned.

 

Have you tried another known good rad just incase it is partly blocked as Anthony says.

[Anthony 1,003]

Actually Tom, looking at it again - one your old setup, is the 2nd heater matrix pipe T'd off the top radiator hose as it looks in the diagram?

 

If so, that was probably allowing it to run cooler than the thermostat rated temperature, as the heater matrix circuit would act as a thermostat bypass. Now that you've plumbed it in properly, the thermostat is regulating temperature, and thus running hotter (perhaps not helped if the 'stat is old and not opening properly)

[feb 47]

Anthony, wouldn't it act as a bypass only when the thermostat is open though?

Doesn't water flow clock wise in the blue pipes?

Only guessing by looking at the diagram.

Edited September 6, 2011 by feb

[Anthony 1,003]

Coolant flows towards the rear coolant distribution block, as that's where the water pump draws coolant in.

 

The heater matrix as it was plumbed in would allow coolant to bypass the thermostat, go through the radiator (cooling it) and then into the waterpump.

 

I imagine that on cruise the thermostat would be closed on the old setup, and all the coolant running through the matrix, hence it running cooler.

 

Now that it isn't bypassing the thermostat, the coolant will always atleast to the thermostat's rated opening temperature.

[feb 47]

It makes sense now, thanks!

[Tom Fenton 1,548]

Cheers for the thoughts guys.

 

I would normally lean towards the rad in this situation, but it was a definite step change between changing the hoses round.

 

I've replaced the stat with the proper Mi one. I have flushed out the rad, it was pretty clear really.

 

Hot wise obviously I am only going on the gauge, but it is running on the 5th bar or the 2nd "heavy" bar, this is too hot for my liking. The Emerald also thinks it is hot as the fan is running a lot.

 

Sitting still it will stay about the same, cruising part throttle it may cool slightly, but full attack and it just gets hotter and hotter.

 

It isn't just as simple as swapping the rad, the one fitted has alloy TIG welded end tanks to a special alloy core to fit in the space available.

 

I think tomorrow I will try putting the pipes back as they were and at least try it. If that doesn't work I'm going to have to make another rad, and sharpish.

[Anthony 1,003]

Did you do the 'stat at the same time as the hoses?

 

If so, I'd be tempted to try another stat first and foremost, ideally an 82 degree normal 8v one - Halfords certainly used to have these on the shelf and cheap as chips if you've got a trade card.

 

Most Mi16 'stats that I've seen have been 89 degree rated, which is usually about halfway or a touch under on the gauge, so you're not massively over that. The mark you meant is marked up as 90 degrees on the Euro style clocks to give you an idea, although clearly the Emerald will give you a more accurate temperature.

 

 

To give you a comparison, my 82 degree 'stat runs on the 4th mark (one below halfway) and the 72 degree SBC 'stat in the engine I've just fitted sits a little over the 3rd mark - so both roughly tie in with the numbers on the above cluster, and if yours is an 89 degree 'stat, it would figure that yours will be not too far off what temperatures you're seeing - assuming I've understood your post correctly.

 

Constantly hot even not under load doesn't sound like the radiator to me.

[Tom Fenton 1,548]

No, I changed the stat for another to see if it would make any improvement, there is no difference. I cannot use the 8v stat as I still have the Mi rear water pipe etc in place.

 

Tomorrow afternoon I will put the hoses back just to satisfy myself one way or another. If that doesn't sort it I'm going to have to investigate either the water pump or make another radiator.....

[Anthony 1,003]

I cannot use the 8v stat as I still have the Mi rear water pipe etc in place.

You can, just means that the bypass rail across the back of the head doesn't work as it should - most Mi16's out there will likely be running 8v 'stats.

 

I'd say that if you put the hoses back to as they were, it'll run cool again, because you're effectively bypassing the 'stat and allowing the engine to run cooler than the thermostat temperature - assuming I'm reading your initial diagram correctly and you T'd off the top radiator hose as it appears.

 

Are the Mi16 'stats that you've got 89 degree rated?

[Tom Fenton 1,548]

Well I re plumbed it last night and it now runs cool again.

 

Can't really explain why, as it runs at 95 or so degrees on the Emerald as it was, it now runs around 80 deg and only gets up to about 90 when it is sat idling after some grief.

 

A job for another day I suppose is to get hold of a different thermostat and see if it will run cool with the proper hoses on there.

 

But for now I need to source the blank for the lower water housing to block of the port I do not need.

[pug_ham 245 3 Cars]

I'm with Anthony on this one, initially your old hose set up was effectively by-passing the thermostat so it would been virtually running without one.

 

But for now I need to source the blank for the lower water housing to block of the port I do not need.

What was on there originally blocking the distribution block unused port off?

 

I assume you're still using the three port Mi block on the back of the engine but could always swap a two port 8v on & use the blank from the third port for the thermostat pipe.

 

g

[Tom Fenton 1,548]

There was a blanking cap, but it had been there since 1989 by the looks of it, and didn't fill me with confidence to say the least!

[pug_ham 245 3 Cars]

fair enough, 1307W4.

 

Hmm, maybe not, just checked price of that part number & its £18.59!!

 

I might have one somewhere.

 

g

Edited September 8, 2011 by pug_ham