Mazda B2600 G6 overheating help please

I have purchased a 1992 mazda bravo 4WD. Since purchasing I have had constant overheating problems. Cylinder head has been replaced twice ( 2 x different heads), block has been replaced, cooling system has been flush repeatedly, thermostate has been replaced, it still overheats even with the thermostate removed. Radiator has been service twice, thermo fan clutch has been replaced. There are no leaks and no water loss. The bottom radiator hose is slightly cooler than the top, so appears as though the water is cooling.Has a new water pump, flow appears normal. The water is circulating and there does not appear to be any blockages. I am going to start bypassing things such as oil cooler and heater core at a last ditch effort, then maybe remove the air cond to try and get some more air flow through the radiator other than that I am at a loss after 10 years as a mechanic I have really lost it with this one Iam open to anyone with any ideas or same type of problems.:banghead:

flushing/flow testing isn't all that reliable. Considering your list of work, I'd say replace the radiator

Removing the t-stat often has the opposite effect many assume. It will take longer to get hot, but will more likely overheat when it does get up to temp. Never remove a t-stat. You need to at the very least, put a restrictor plate in place of it. There is definitely such a thing as too much flow in a coolant system!

flushing/flow testing isn't all that reliable. Considering your list of work, I'd say replace the radiator

Removing the t-stat often has the opposite effect many assume. It will take longer to get hot, but will more likely overheat when it does get up to temp. Never remove a t-stat. You need to at the very least, put a restrictor plate in place of it. There is definitely such a thing as too much flow in a coolant system!


Thanks Uncle Bob I agree that this may be and option, I am going to change the water pump tomorrow, It is circulating but does not appear to be much. It only has a single core radiator in it. So it could probably do with a bigger one anyway. I am still ata real loss though. I stood and watched the service get done on the radiator the second time and it flowed throgh really well. The radiator isnt new but appears to be okay. If the water pump doesnt fix it a new radiator is going in. Its really starting to rack up the dollars now:runaround:

you can have very good flow through a radiator but still have very poor heat transfer efficiency. Either due to scaling that the flush agent didn't remove and/or from large sections of the radiator still being plugged.

Think of a 2" ID pipe flowing coolant. It will flow extremely well, but it won't do crap for heat transfer. Flow is only one factor in proper heat transfer

you can have very good flow through a radiator but still have very poor heat transfer efficiency. Either due to scaling that the flush agent didn't remove and/or from large sections of the radiator still being plugged.

Think of a 2" ID pipe flowing coolant. It will flow extremely well, but it won't do crap for heat transfer. Flow is only one factor in proper heat transfer

The more i think about I think you may be right I have been looking for a new radiator thanks for your help

The more i think about I think you may be right I have been looking for a new radiator thanks for your help


Thanks uncle Bob, you saved my sanity, I cant believe that I had a radiator to a trusted service centre twice and it can still be faulty. Thanks mate for your help the new radiator fixed the problem. .:grinno:

Glad it worked :)