14 replies to this topic

[zero_wlv]

Hi everyone,

 

I've been trying to track down the cause of persistent overheating on my 998cc 1989 Mini.

For the last 9 months or so,  it's only been able to drive for 20 minutes or so before the needle touches 100degC (it's a newly fitted Tim gauge so should be fairly accurate).

So in practical terms the car's not really usable.

 

Well this afternoon I tore the water pump off,   the pump turned out to be in perfect condition being only 4 years old.

But there's a strange rusty hole in the volute of the pump cavity     (see attached photo).

 

 mini water pump.jpg   35.18K   7 downloads

 

My questions are:

 

     - is it common for the engine block to rust through here?

     - where does this hole go to?     I don't think I've had any oil in my coolant or coolant in my oil

     - is it sufficient cause for the engine to begin to overheat after 20mins?     (probably a silly question)

     - can a workshop fix it?     (probably an even sillier question)

 

I bought the engine as fully reconditioned 4 years ago;    it always seems to have had problems with brown rusty coolant.

When I drained the coolant today it was in a particularly bad state,     the last time I changed it was Nov 2021 with a 50:50 mix.

I'm not sure why the coolant's so bad this time,   maybe because the car's only been out for 3 short trips since November   (simply because I haven't had time to investigate the overheating issue).

 

Thanks in advance,

Liam

 

 

[nicklouse]

Have you actually checked the temperature by other means?

 

IIRC. That is just casting flash in part of the water jacket. If I am seeing what I think I am. It is far away and not well lite.

[zero_wlv]

Have you actually checked the temperature by other means?

 

IIRC. That is just casting flash in part of the water jacket. If I am seeing what I think I am. It is far away and not well lite.

 

I took quite a few measurements with an infra-red gun  (at a point on the engine block just below the thermostat housing),   it agrees reasonably well with what the temp gauge is saying.

 

I've added what is hopefully a clearer photo below,    a screwdriver can be poked right through the hole into a cavity.    I'm not sure where the cavity leads to though.     

 

If it's usual to have the hole there that's great,   it just means I'll have to look elsewhere to solve the overheating  (coolant passages or head gasket perhaps).

 

 mini water pump detail.jpg   47.72K   6 downloads

Edited by zero_wlv, 04 June 2022 - 09:35 PM.

[klivins]

There's coolant jackets all around the cylinders. Even if that was another hole, that should not affect cooling. 100 degree is a tad too much, but nothing extraordinary.
Does it go higher, and actually boil?
Is everything else correct? Fan correct way around?

[nicklouse]

 

Have you actually checked the temperature by other means?

 

IIRC. That is just casting flash in part of the water jacket. If I am seeing what I think I am. It is far away and not well lite.

 

I took quite a few measurements with an infra-red gun  (at a point on the engine block just below the thermostat housing),   it agrees reasonably well with what the temp gauge is saying.

 

I've added what is hopefully a clearer photo below,    a screwdriver can be poked right through the hole into a cavity.    I'm not sure where the cavity leads to though.     

 

If it's usual to have the hole there that's great,   it just means I'll have to look elsewhere to solve the overheating  (coolant passages or head gasket perhaps).

 

mini water pump detail.jpg

 

That ain’t a problem.

[slidehammer]

Maybe you just need to give the block, heater and radiator a good flush through with a hose pipe in both directions if you are getting a lot of rust in the coolant. It might be worth checking with your heat gun the temperature over all the radiator as it might be sludged up and need replacing.

[zero_wlv]

There's coolant jackets all around the cylinders. Even if that was another hole, that should not affect cooling. 100 degree is a tad too much, but nothing extraordinary.
Does it go higher, and actually boil?
Is everything else correct? Fan correct way around?

 

It creeps up above 100deg and looks as though it's not gonna stop,    I've bailed out at 105 every time and pulled over!      So it hasn't actually boiled as such,  but I'm sure it would if I carried on driving.

The fan is definitely the correct way  (ribs facing the outside).

 

 

Maybe you just need to give the block, heater and radiator a good flush through with a hose pipe in both directions if you are getting a lot of rust in the coolant. It might be worth checking with your heat gun the temperature over all the radiator as it might be sludged up and need replacing.

 

I already tried flushing it a couple of times (once with Wynn's rad flush, once with white vinegar and also plenty of water) but I'll give it another go.

Would there be any point in taking the head off and poking through the coolant passages with pipe cleaners?

[slidehammer]

 

There's coolant jackets all around the cylinders. Even if that was another hole, that should not affect cooling. 100 degree is a tad too much, but nothing extraordinary.
Does it go higher, and actually boil?
Is everything else correct? Fan correct way around?

 

It creeps up above 100deg and looks as though it's not gonna stop,    I've bailed out at 105 every time and pulled over!      So it hasn't actually boiled as such,  but I'm sure it would if I carried on driving.

The fan is definitely the correct way  (ribs facing the outside).

 

 

Maybe you just need to give the block, heater and radiator a good flush through with a hose pipe in both directions if you are getting a lot of rust in the coolant. It might be worth checking with your heat gun the temperature over all the radiator as it might be sludged up and need replacing.

 

I already tried flushing it a couple of times (once with Wynn's rad flush, once with white vinegar and also plenty of water) but I'll give it another go.

Would there be any point in taking the head off and poking through the coolant passages with pipe cleaners?

 

You could pull the head, but if you are not getting a lot of sludge when you have previously fushed the system, it would probably be pointless

[zero_wlv]

 

slidehammer, on 05 Jun 2022 - 02:36 AM, said:

You could pull the head, but if you are not getting a lot of sludge when you have previously fushed the system, it would probably be pointless

 

 

I just spent a couple of hours pulling the head :)

 

I'm not really sure what the photos are telling me,  I'm not experienced enough, except perhaps that everything could do with de-coking and one of the exhaust valves looks lean.

 

I don't know if there's anything that could cause overheating.

(p.s. the engine's only done 6400 miles since it was reconditioned, although it looks like a lot more!)

 

BLOCK WITH GASKET:

 

 block with gasket.jpg   72.06K   11 downloads

 

BLOCK WITH GASKET TAKEN OFF:

 

 block without gasket.jpg   76.4K   14 downloads

 

HEAD:

 

 head 1.jpg   62.68K   19 downloads

 

HEAD DETAIL:

 

 head detail.jpg   76.35K   9 downloads

 

BLOCK DETAIL:

 

 block detail.jpg   74.45K   6 downloads

 

 

 

Edited by zero_wlv, 05 June 2022 - 07:29 PM.

[sonscar]

From the pictures it looks to me that the only cylinder running anything near right is the one you thought was lean.Looks like gasket failure between 2&3 and water jacket and 4.Photos can be deceiving but looks excessively rich and probably badly worn now,Could be wrong though,Good luck,Steve..

[nicklouse]

Looks like you have a recessed exhaust valve or two there.

[zero_wlv]

Looks like you have a recessed exhaust valve or two there.

 

I'm not really sure what this means,   what are the implications of it?

 

When I bought the reconditioned engine it was described as "high compression",  although I believe this was achieved by using high compression pistons.

It's a 12G940 large valve cylinder head (off a 1275cc?) on a slightly overbored 998cc block.

[nicklouse]

 

Looks like you have a recessed exhaust valve or two there.

 

I'm not really sure what this means,   what are the implications of it?

 

When I bought the reconditioned engine it was described as "high compression",  although I believe this was achieved by using high compression pistons.

It's a 12G940 large valve cylinder head (off a 1275cc?) on a slightly overbored 998cc block.

 

The head, yes 1275, needs a recondition. Or at least looking at by someone who knows the A series build. 
 

one exhaust valve seems to be sitting low in the head. This could be wear or could be intentional to aid the clearance to the block where it may not have been quite pocketed enough to give clearance.

[panky]

Make sure when you you put it back together you use a 1275 head gasket. A small bore gasket will partially cover pockets that have been machined in your block. The 12G940 you have head is normally fitted to a 1275 engine and the valve spacing is wider to that on the small bore engines hence the pockets to give the exhaust valve clearance on your engine.

[Spider]

I can't say with any certainty but that hole you've found may have some impact on the cooling as the pump does rely on the shape of the casting in the block to direct the coolant from the impellar correctly. I wouldn't be too fast to write that off.  You maybe able to prove it by re-building it with one of the plastic metals.

 

Some other common causes of running hot are;-

 

rusted cooling jacket

chocked cooling system

blown head gasket

incorrect timing and / or advance curve

incorrect fuel mixture (carb needle)

vacuum leak

cracked head

cracked block