1991 Mazda T 3500 4 cylinder diesel motor home. Problem!
The motor doesn't reach a temp much above, (on the gauge) 60 deg. I have had the radiator replaced, and have replaced the thermostat 3 times. Belts and water levels are checked regularly.
The fan drive "boss" has also been replaced, as I was told the system is "over cooling" !!??
I have had the entire heater unit out from under the dash, four times. (Bugger of a job)
In cold weather, I can't get any heat into the cab, plus demisters are useless. But....if I blank off two thirds of the radiator, the temp. jumps up to about 90 to 100 deg.
If I restrict the fan speed by looping a leather belt around the fan "boss", the motor heats up!!!???
If the motor isn't hot, it smokes. But, like all older diesels, when hot, no smoke.
With todays prices on mechanics, do not want to get caught out by some no hoper. Any ideas?
Pipes.
macka17 said
11:42 AM Apr 18, 2017
Well.
Yrs ago in "The old country".
Too much cooling was a problem at times through the outside temp's.
A lot fitted a fixed blind\cover over bottom of radiator grill.
Some of us fitted a roll up\down externall blind..
Outside rad. inside grill.
so it was adjustable. according to driving and temp's.
You OVER cooling lad.
don't knock it. That's a bonus.
Just adjust frontal airflow to suit temp's.
IE.. NOT 2 thirds of rad.
JUST the area needed. Trial and error.
Coldest water\air, is at bottom of rad.
Cool from there. Maybe some Ally sheeet.
or even cardboard to get the sizing.
But fit a proper "Water temp Guage" first.
Those on dash ain't worth a gnats toss.
PS. Read up on working temp's on diesel engines.
Mazda forums would be good.
75 to 90ish max under load, is good.
I've seen some in the 100 range and still fine.
As long as they don't stay there long,
like climbing a hill.
Those older donk's are pretty robust.
Warren-Pat_01 said
02:55 PM Apr 18, 2017
Pipes, I assume you have the correct thermostat fitted (it can be checked on stove). I cracked a head (in the pre-combustion chambers) on my MQ Nissan once when I hit a hail storm north of Adelaide & the thermostat was jammed open.
If you cover half of your radiator with a sheet of news paper, does the temperature gauge move, car gets warmer?
Macca's advice is tops.
swamp said
03:35 PM Apr 18, 2017
Hi sounds like u have done most things .
The factory gage could be be lying to u . Verify with a different gage .
Running an engine cold
wears it out faster
floods with fuel more accelerator pedal to get going
poor economy / performance
As u have done radiator in good condition
Viscous hub NOT locking up
THERMOSTAT NEEDS CHECKING for opening temp
crank /w/pump/ Pulley ratio verified . Panel beaters are not mechanics
Noticed they say these hi flow thermostats " eliminate the need to run cooler thermostats "
All these hi flows have a 77c operating group temp .... might be worth a try
Mike Harding said
04:25 PM Apr 18, 2017
I *very* strongly advise you to use another method of measuring the engine temperature before you start covering the radiator otherwise you may destroy a perfectly good engine to prove the temperature measurement system is faulty.
Older engine temperature measurement was performed by a temperature sensitive resistor causing the current through a meter to vary. The meter/TSR were fed from a crude voltage stabiliser; any one of those or their connectors could be at fault and they were never accurate to begin with.
Beg or borrow a temperature meter which uses a thermocouple (many multimeters have this feature nowadays) and, with a cold engine, remove the radiator cap and place the thermocouple in the coolant. Bring the engine up to temperature (it doesn't sound as though it will reach boiling point) and note the reading from the thermocouple. Also note the temperature gauge in the instrument cluster.
Remove the thermocouple from the radiator and loosen one of the thermostat housing bolts enough to trap the thermocouple under it - retighten. Bring the engine up to working temperature again and note the reading from the thermocouple.
If there is, say, a 15C difference between the two readings you can now establish, with acceptable accuracy, the true temperature of the coolant with an external measurement. Replace the radiator cap and see if that makes a difference.
Check in the workshop manual what the working coolant temperature should be (I'll guess around 95C) and now you can block the radiator off with some confidence you know the true temperature of the coolant.
Keep very much in mind that the relationship between the amount of radiator area blocked and coolant temperature is probably not linear. So a 30% block may be fine on a 25C day on the flat but on a 35C day and a couple of long steep hills it may be too much.
Mazda don't design engines to run cold so if all the bits (radiator, thermostat etc) are the correct parts then I'd be looking to find the real cause not trying to put a Band Aid on it.
PS. Whilst you have the meter/thermocouple put the thermostat and thermocouple in a saucepan of water on the gas stove and note at what temperature the thermostat opens.
-- Edited by Mike Harding on Tuesday 18th of April 2017 04:25:31 PM
Bagmaker said
06:07 PM Apr 18, 2017
The thermostat is incorrect or being bypassed pipes, bad thing.
No heating to cab (first indicator that gauge is correct)
incorrect running temperature for motor = premature wear issues.
Have it re-checked by someone competent and send the bill to your last mechanic
Jaahn said
07:53 AM Apr 19, 2017
Hi pipes
Some good advice given already, but you say it has all been checked. So think outside the box for a bit !!
All engines diesel and petrol have the cooling capacity to stay too cold if the thermostat system does not work as it should. They should stay hot driving in the snow and ice and work OK. Trucks may need some manual radiator covering in extreme cold conditions but we do not have them here in Australia. So the only conclusion to say is your thermostat and cooling system IS NOT WORKING PROPERLY.
Some engines do have a slightly more complicated coolant flow than others. Some thermostats are dual action and open up on one side and close the other side to prevent flow. Go to a Mazda agent and make sure you have the exact one for that engine, not just the temperature setting but the physical design too. Fitting a simple one instead of a dual action one will cause problems. The one shown in the link above is a dual action unit.
It is also possible that the internal heater hoses and connections may be incorrectly fitted so the water is always flowing and cooling it when it should not. The bus had several heater units fitted in the back originally and these may be still connected somewhere underneath or the hoses are incorrectly directed. The internal heaters are connected to the thermostat bypass circuit so will cause overcooling if incorrectly piped. These old buses and trucks, Mazda and (Ford brand too) were good workers and usually no problems.
Jaahn
-- Edited by Jaahn on Wednesday 19th of April 2017 07:58:59 AM
pipes said
06:33 PM Apr 19, 2017
The heating system into the cab is COLD.
But when I partially blank off the radiator, then the hot air gets into the cab.
Had a mechanic turn up with one of those "things" that look like a pistol. He pointed it at the thermostat housing, when the motor was hot, and declared that the thermostat was A, OK ?
New fuel filters.
New air filters.
"Diesel Plus" with every tank full.
At 80 kph, on the Nullabor, I get 10 kpl !
85/90, and I get 7 kpl.
Pipes.
erad said
08:59 PM Apr 19, 2017
The mechanic's tool he used was a remote infra-red temperature sensor. It would show the temperature of the thermostat housing. The fact that your temperature gauge says 60 Deg C (however inaccurate it is) and that you cannot get any heat inside the cabin tells me that the thermostat is stuck open.
I cannot see any reliable way of diagnosing a thermostat stuck open other than to remove and inspect it. Then stick it in a saucepan of water and boil it up. You should see it closed when it comes out, and then when it gets hot (typically around 78 Deg C), it should start to open . Typically at around 90 Deg C it should be fully open (the valve disc should have moved 8 to 10 mm open). Then, when it cools it should close again. If it doesn't do that, it is stuffed and needs replacing. Since you are getting no heat inside the heater (other than when you partially blank off the radiator), I would say that the thermostat is stuck open and needs replacing.
pipes said
02:03 PM Apr 21, 2017
Thanks to all for your input.
Pipes.
Tony Bev said
03:36 PM Apr 21, 2017
Hello Pipes
Usual disclaimer, that I am not a mechanic, but cheeky enough to try and find out, how things work
As I travel with a thermal temperature gauge in my armoury, (it looks like a gun).
The next time we bump into each other, we can play around to our hearts content, to see exactly where the hot water from the engine, starts cooling.
In the meantime if you do cure the problem, can you let us all know how it was done, as there are other travellers, who have the same vehicle as yourself
As a sidenote, I hope that you have had your back operation, and that you are well on the way to making a full recovery
1991 Mazda T 3500 4 cylinder diesel motor home. Problem!
The motor doesn't reach a temp much above, (on the gauge) 60 deg. I have had the radiator replaced, and have replaced the thermostat 3 times. Belts and water levels are checked regularly.
The fan drive "boss" has also been replaced, as I was told the system is "over cooling" !!??
I have had the entire heater unit out from under the dash, four times. (Bugger of a job)
In cold weather, I can't get any heat into the cab, plus demisters are useless. But....if I blank off two thirds of the radiator, the temp. jumps up to about 90 to 100 deg.
If I restrict the fan speed by looping a leather belt around the fan "boss", the motor heats up!!!???
If the motor isn't hot, it smokes. But, like all older diesels, when hot, no smoke.
With todays prices on mechanics, do not want to get caught out by some no hoper. Any ideas?
Pipes.
Yrs ago in "The old country".
Too much cooling was a problem at times through the outside temp's.
A lot fitted a fixed blind\cover over bottom of radiator grill.
Some of us fitted a roll up\down externall blind..
Outside rad. inside grill.
so it was adjustable. according to driving and temp's.
You OVER cooling lad.
don't knock it. That's a bonus.
Just adjust frontal airflow to suit temp's.
IE.. NOT 2 thirds of rad.
JUST the area needed. Trial and error.
Coldest water\air, is at bottom of rad.
Cool from there. Maybe some Ally sheeet.
or even cardboard to get the sizing.
But fit a proper "Water temp Guage" first.
Those on dash ain't worth a gnats toss.
PS. Read up on working temp's on diesel engines.
Mazda forums would be good.
75 to 90ish max under load, is good.
I've seen some in the 100 range and still fine.
As long as they don't stay there long,
like climbing a hill.
Those older donk's are pretty robust.
If you cover half of your radiator with a sheet of news paper, does the temperature gauge move, car gets warmer?
Macca's advice is tops.
Hi sounds like u have done most things .
The factory gage could be be lying to u . Verify with a different gage .
Running an engine cold
wears it out faster
floods with fuel more accelerator pedal to get going
poor economy / performance
As u have done radiator in good condition
Viscous hub NOT locking up
THERMOSTAT NEEDS CHECKING for opening temp
crank /w/pump/ Pulley ratio verified . Panel beaters are not mechanics
Is the engine running fine in hot weather
Compressions verified
Injector pump and injectors serviced , Injector pump lift / timed correctly
Many thanks.
Pipes.
Noticed they say these hi flow thermostats " eliminate the need to run cooler thermostats "
All these hi flows have a 77c operating group temp .... might be worth a try
I *very* strongly advise you to use another method of measuring the engine temperature before you start covering the radiator otherwise you may destroy a perfectly good engine to prove the temperature measurement system is faulty.
Older engine temperature measurement was performed by a temperature sensitive resistor causing the current through a meter to vary. The meter/TSR were fed from a crude voltage stabiliser; any one of those or their connectors could be at fault and they were never accurate to begin with.
Beg or borrow a temperature meter which uses a thermocouple (many multimeters have this feature nowadays) and, with a cold engine, remove the radiator cap and place the thermocouple in the coolant. Bring the engine up to temperature (it doesn't sound as though it will reach boiling point) and note the reading from the thermocouple. Also note the temperature gauge in the instrument cluster.
Remove the thermocouple from the radiator and loosen one of the thermostat housing bolts enough to trap the thermocouple under it - retighten. Bring the engine up to working temperature again and note the reading from the thermocouple.
If there is, say, a 15C difference between the two readings you can now establish, with acceptable accuracy, the true temperature of the coolant with an external measurement. Replace the radiator cap and see if that makes a difference.
Check in the workshop manual what the working coolant temperature should be (I'll guess around 95C) and now you can block the radiator off with some confidence you know the true temperature of the coolant.
Keep very much in mind that the relationship between the amount of radiator area blocked and coolant temperature is probably not linear. So a 30% block may be fine on a 25C day on the flat but on a 35C day and a couple of long steep hills it may be too much.
Mazda don't design engines to run cold so if all the bits (radiator, thermostat etc) are the correct parts then I'd be looking to find the real cause not trying to put a Band Aid on it.
PS. Whilst you have the meter/thermocouple put the thermostat and thermocouple in a saucepan of water on the gas stove and note at what temperature the thermostat opens.
-- Edited by Mike Harding on Tuesday 18th of April 2017 04:25:31 PM
No heating to cab (first indicator that gauge is correct)
incorrect running temperature for motor = premature wear issues.
Have it re-checked by someone competent and send the bill to your last mechanic
Hi pipes
Some good advice given already, but you say it has all been checked. So think outside the box for a bit !!
All engines diesel and petrol have the cooling capacity to stay too cold if the thermostat system does not work as it should. They should stay hot driving in the snow and ice and work OK. Trucks may need some manual radiator covering in extreme cold conditions but we do not have them here in Australia. So the only conclusion to say is your thermostat and cooling system IS NOT WORKING PROPERLY.
Some engines do have a slightly more complicated coolant flow than others. Some thermostats are dual action and open up on one side and close the other side to prevent flow. Go to a Mazda agent and make sure you have the exact one for that engine, not just the temperature setting but the physical design too. Fitting a simple one instead of a dual action one will cause problems. The one shown in the link above is a dual action unit.
It is also possible that the internal heater hoses and connections may be incorrectly fitted so the water is always flowing and cooling it when it should not. The bus had several heater units fitted in the back originally and these may be still connected somewhere underneath or the hoses are incorrectly directed. The internal heaters are connected to the thermostat bypass circuit so will cause overcooling if incorrectly piped. These old buses and trucks, Mazda and (Ford brand too) were good workers and usually no problems.
Jaahn
-- Edited by Jaahn on Wednesday 19th of April 2017 07:58:59 AM
But when I partially blank off the radiator, then the hot air gets into the cab.
Had a mechanic turn up with one of those "things" that look like a pistol. He pointed it at the thermostat housing, when the motor was hot, and declared that the thermostat was A, OK ?
New fuel filters.
New air filters.
"Diesel Plus" with every tank full.
At 80 kph, on the Nullabor, I get 10 kpl !
85/90, and I get 7 kpl.
Pipes.
I cannot see any reliable way of diagnosing a thermostat stuck open other than to remove and inspect it. Then stick it in a saucepan of water and boil it up. You should see it closed when it comes out, and then when it gets hot (typically around 78 Deg C), it should start to open . Typically at around 90 Deg C it should be fully open (the valve disc should have moved 8 to 10 mm open). Then, when it cools it should close again. If it doesn't do that, it is stuffed and needs replacing. Since you are getting no heat inside the heater (other than when you partially blank off the radiator), I would say that the thermostat is stuck open and needs replacing.
Pipes.
Usual disclaimer, that I am not a mechanic, but cheeky enough to try and find out, how things work
As I travel with a thermal temperature gauge in my armoury, (it looks like a gun).
The next time we bump into each other, we can play around to our hearts content, to see exactly where the hot water from the engine, starts cooling.
In the meantime if you do cure the problem, can you let us all know how it was done, as there are other travellers, who have the same vehicle as yourself
As a sidenote, I hope that you have had your back operation, and that you are well on the way to making a full recovery