I am battling an overheating issue on a 71 240 with 2.8 block, E31 head

Back ground: the car was sitting for almost 19 years, got it gunning and driving couple of month a go.

Replaced the radiator with a now 3 core aluminium job (came with a cap), also took it to a radiator shop and tested for flow, its perfect.

replaced water pump (bearing was gone)

new thermostat

Mechanical fan, good clutch

back flushed the system

car was running hot and overheating so I  picked up a block test, sure enugh it turned yellow.

Pulled the head, got it surfaced (8 thou) resembled everything with NO thermostat.

Drove it today (T shirt weather) just took it around the block, 3 miles or so, when I got gack the gage was over 3/4, popped the hood sure enugh the upper hose is very hot, lower hose is cold as if the thermostat is closed, let it cool for 15 minutes, removed cap and start the engine, no water flow at all as if the water pump is not working,

Some digging on line and found that some had issues with the impeller separating on water pumps...great, off with the pump ...if you guested that the impeller was perfect you would be right! (I was hoping it came off)

So now what? I'm at the end of the rope here ! Any advice is welcomed.

The only things that I didn't try is to replace is the radiator cap but I don't see how can it cause the issue. there is nothing left to replace.....but the engine.

When the car was parked it drove like a scalded ape and it still does, the only issue is the overheating which did not exist when it was parked.

 

So sitting all those years was the system sealed? No critters could have gotten in? Do you have the heater core bypassed?

Also someone replaced their radiator recently and accidentally blocked it causing overheating issues. You sure that’s not the case? Not dinging you in anyway.

Edited January 30, 20187 yr by JSM

I would replace the radiator if you have a spare laying around. Or the radiator cap...

I suspect trash from the block has blocked up the new radiator.

It sat in socal in a garage under a cover, the system was sealed, zero critters. the heater core is bypassed.

1 minute ago, Patcon said:

I would replace the radiator if you have a spare laying around. Or the radiator cap...

I suspect trash from the block has blocked up the new radiator.

Like I said I just took the radiator to get if flow tested(its new but just incase),  its 100% 

If it were me, I would remove the upper and lower rad hoses.  Adapt a fitting to the upper radiator hose so you can run a garden hose to it. Run it for awhile to see how the flow is coming out and any crud. There isn’t much left. 

15 minutes ago, tzagi1 said:

heater core is bypassed.

Search these words and you might find something.  Might not be the source of your problem but the results will be worth reading, long-term.

Already flushed it with a diluted mixture of muriatic acid and water, neutralised it with a mixture of baking soda and water, then back flush it again, nothing dramatic came out at any flush.

One thing I forgot, I did remove the block drain plug, its almost solid behind it, the water just trickles out, When I took the head off I verified that all the water passages between the block and the head were clean and clear, again, nothing was clogged.

2 minutes ago, tzagi1 said:

Already flushed it with a diluted mixture of muriatic acid and water, neutralised it with a mixture of baking soda and water, then back flush it again, nothing dramatic came out at any flush.

One thing I forgot, I did remove the block drain plug, its almost solid behind it, the water just trickles out, When I took the head off I verified that all the water passages between the block and the head were clean and clear, again, nothing was clogged.

Priori to the overheating or after? Flushing vs getting it hot running much more things could loosen up. 

2 minutes ago, Zed Head said:

Search these words and you might find something.  Might not be the source of your problem but the results will be worth reading, long-term.

It was doing the same thing when it wasn't bypassed, I just by passed it to do the flush(didn't want acid in a brand new core) and did not reconnect it yet.

1 minute ago, JSM said:

Priori to the overheating or after? Flushing vs getting it hot running much more things could loosen up. 

After, I just drained it today to remove the water pump, water is crystal clear with no sediments.

4 minutes ago, tzagi1 said:

It was doing the same thing when it wasn't bypassed, I just by passed it to do the flush(didn't want acid in a brand new core) and did not reconnect it yet.

The dilemma is if you do fix the problem you might not know it because you've created another known overheating situation.