15 replies to this topic

[dan1zo]

Hey fellow enthusiats.

Ive been having issues with my 98 mpi overheating for the last 12 months. It started sporadically but now i need to do something about it now i have the time.

Today i changed the oil, it hadn't been done for ages. Was black and gross. Put in 20w50.
Ive also had the radiator out and checked for leaks, cleaned it out. Flushed the coolant. Checked the water pump and all seems ok.
Today something bad seemed to happen. I ran it up to temperature and all seemed ok to begin with. Fan came on as expected but i went to check in the engine and i could tell the water was boiling. And saw water leaking.

What i though was water spraying from the radiator was in fact spraying from the engine block. Have a look at the picture.
How serious is this? Something blocked in the coolant flow in the block?

Are we looking engine out or is it dead?

Attached Files

•  IMG20260502152121.jpg   61.7K   12 downloads

[primrose8]

That’s a core plug it’s leaking from, not too serious probably corroded, you can buy the core plugs and replace it in situ

[dan1zo]

That’s a core plug it’s leaking from, not too serious probably corroded, you can buy the core plugs and replace it in situ

Ok well thats good at least. But with the overheating, is it likely that the waterways are blocked and preventing proper coolant flow? I guess that would need more investigation?

[sonscar]

When you remove the core plugs you can access some of the waterways and poke them cleaner.Steve..

[lsto]

If one core plug has failed then change all of them whilst your there, I did mine recently because one was leaking and they were all in poor condition. If you have an overheating problem then first things first check the coolant level, obviously you already found a leak. Next change the thermostat, they are cheap and easy to change.

[Wiggy]

What is the temperature gauge doing?

Side note: I'd pull the heater core & flush that out of the car. Mine was a absolutely chock full so I replaced it. The hot / cold valve in the car gets stiff if it's full.

[pete l]

With a water leak, you won't be getting the system under pressure, so it will boil.

[dan1zo]

Hey guys thanks for the feedback. Im getting that core plug sorted. It was overheating before that though. So ive also checked the expansion tank cap and replaced that too. Could be that was stuck open. I didn't realise it was so sensitive to pressure change.
Heater matrix is definitely clear. I don't have the standard heater unit anymore.

[dan1zo]

What is the temperature gauge doing?

Side note: I'd pull the heater core & flush that out of the car. Mine was a absolutely chock full so I replaced it. The hot / cold valve in the car gets stiff if it's full.

It was getting up to normal mid temperature and fan was kicking in as usual. Then after a while it would just shoot up to the red. 

Im guessing it is a pressure issue. So once the core plug is sorted, hopefully is ok and it was the expansion cap.

[dan1zo]

If one core plug has failed then change all of them whilst your there, I did mine recently because one was leaking and they were all in poor condition. If you have an overheating problem then first things first check the coolant level, obviously you already found a leak. Next change the thermostat, they are cheap and easy to change.

I missed this and finally pulled the thermostat. It was in VERY poor condition.

I tested it in boiling hot water and it didnt open, so i've got a new one coming.

 

I managed to change the 2 front core plugs, but how the heck do you do the 2 side ones? Are they only going to be accessible with the engine out? I'm guessing getting them out wont be a problem, but seating the new ones might be difficult from an access perspective.

[dan1zo]

Thanks for the feedback from everyone.

New thermostat installed and when i tested, i found that the temperature sensor had also failed (fan was on constantly). So now with those both replaced it looks like the overheating is resolved.

So with that, the expansion cap might have been ok, but i have a new one anyway now.

 

For future reference on MPI.

Overheating - check first the thermostat. Then the sensor. Then the expansion cap.

All the time doing a good flush of the system. I found it way easier to do with the thermostat housing off. there wasnt much gunk really. so surprisingly clean.

[Quinlan minor]

I'd add "Check plastic header tank for leaks" to the list'

HIKT

 

 

Attached Files

•  Header Tank Pin Hole 2 (small).jpg   30.33K   0 downloads

[dan1zo]

Wow what happened to that?

 

I cleaned my header tank ages ago by putting rice and cold water in it and giving it a good shake.

Got rid of a bunch of the residue inside it.

[Quinlan minor]

Wow what happened to that?

 

I cleaned my header tank ages ago by putting rice and cold water in it and giving it a good shake.

Got rid of a bunch of the residue inside it.

A pinhole in the header tank, sadly not uncommon, the joints often split, too.

The rustalactite indicates it had been weeping for some time. It was only when pressure started dropping, as the hole got bigger, that it started boiling over after shutdown.

Investigations revealed the cause and a new tank was the cure..

[dan1zo]

In addition to this topic, some other things i had found.

 

I found that the water pump may not have been working correctly, the belt tension was very loose and i suspect slipping under load.  Additionally (in another topic) i had a bolt that was rubbing on the water pump pulley from an engine steady attached to it.

So with those fixed i gave it a run.  It still overheated, but i tested again with my OLD header tank cap. I took the new one off and the plastic was 'soft' when it was warm. I also think that the pressure valve in it was too low and leaking, causing the coolant to boil.

 

All of this seems to have fixed it. And i guess new header caps are not always as advertised!!