743b

[raylg]

Hi,First time user. I am working on a 743b that the coolant temp gauge gradually shows hotter than normal.I replaced the thermostat...had the radiator cooked out...replaced the gage and sending unit...checked all the grounds and replaced the wire from the sender to the gage.the Gage will gradually run up to the uncomfortable mark on the gage, wide open no load. The engine shows no other signs of over heating but the gage reading hot...I checked the outside temp of the engine with a infared thermometer and only get 173 deg at the radiator... any guidance will help.

 

[skidsteer.ca]

I'd start with a new guage and sender from a auto parts store. Infared is helpfull but can't get inside the engine. But at this point it sounds like the guage system.
Does the temp come down if you stop working a idle the engine? It may also be a case of everthing in the machine gradually getting warmer then the cooling system being unable to keep ahead of it all.
skidsteer.ca

 

[Tazza]

I'd start with a new guage and sender from a auto parts store. Infared is helpfull but can't get inside the engine. But at this point it sounds like the guage system.
Does the temp come down if you stop working a idle the engine? It may also be a case of everthing in the machine gradually getting warmer then the cooling system being unable to keep ahead of it all.
skidsteer.ca

You didn't mention the water pump, could it be bad?
Generally over heating is due to a cooling system fault, you have mentioned you have done everything except for the water pump. You can even try running it without a thermostat, see what it does, they can stick, even when new. Another cause is a cracked head or leaking head gasket. yet another other cause is over loading the engine, but as you said it was just running open, there isn't much load to cause it to get hot.

 

[raylg]

You didn't mention the water pump, could it be bad?
Generally over heating is due to a cooling system fault, you have mentioned you have done everything except for the water pump. You can even try running it without a thermostat, see what it does, they can stick, even when new. Another cause is a cracked head or leaking head gasket. yet another other cause is over loading the engine, but as you said it was just running open, there isn't much load to cause it to get hot.

Yes the water pump was replaced 2 years ago but I did pull it off and checked the impeller every thing looked good,I also ran it without the thermostat with no change.There is no coolant being pushed into the surge tank and no bubbles eather...Im confused.Is there a way to install a mechanical gage in the thermostat housing where the large threadad plug is..

 

[skidsteer.ca]

Yes the water pump was replaced 2 years ago but I did pull it off and checked the impeller every thing looked good,I also ran it without the thermostat with no change.There is no coolant being pushed into the surge tank and no bubbles eather...Im confused.Is there a way to install a mechanical gage in the thermostat housing where the large threadad plug is..

There likely is not room for bulb of a mech guage inside the housing, or at least you would want to check it closely. The electric guages have a small 1/8” npt sender, where the mechanical guages need at least 3/8 npt and some are 1/2 npt.
Ken

 

[raylg]

There likely is not room for bulb of a mech guage inside the housing, or at least you would want to check it closely. The electric guages have a small 1/8” npt sender, where the mechanical guages need at least 3/8 npt and some are 1/2 npt.
Ken

This engine has a large bolt with a aluminum or some type of soft sealing washer on it, I will double check the size, but it takes a wrench larger than 18mm to fit the head.This bolt goes in the thermostat housing just under the thermostat,if I could find an adapter to fit that I would try a mechanical gage.

 

[Tazza]

This engine has a large bolt with a aluminum or some type of soft sealing washer on it, I will double check the size, but it takes a wrench larger than 18mm to fit the head.This bolt goes in the thermostat housing just under the thermostat,if I could find an adapter to fit that I would try a mechanical gage.

I know the plug you are talking about. It wouldn't hurt to pull it out and see if you can get something to suit the threads.
You have done everything right, i'm with Ken on this one, your gauge or sender may be bad.
I assume the cooling fan has all its blades still?

 

[raylg]

I know the plug you are talking about. It wouldn't hurt to pull it out and see if you can get something to suit the threads.
You have done everything right, i'm with Ken on this one, your gauge or sender may be bad.
I assume the cooling fan has all its blades still?

I did look at the cooling fan blades when I had the raadiator out,they look good and it will blow your hat off.I agree it seems to be a gage/sender problem and its on its second pair back to back and they both read the same,maby I should install a resistor in the sender wire but why.. to me it just seems like this should be a simple fix... challenging.

 

[Jyuma]

I did look at the cooling fan blades when I had the raadiator out,they look good and it will blow your hat off.I agree it seems to be a gage/sender problem and its on its second pair back to back and they both read the same,maby I should install a resistor in the sender wire but why.. to me it just seems like this should be a simple fix... challenging.

You didn't mention if you had any coolant loss? If you are not loosing coolant then I'd rule out cracked heads or blown head gaskets. If you do have some coolant loss then I'd check hoses and clamps first, before looking for head or gasket problems.
I wouldn't trust “cooking“ the radiator. There are too many ways a radiator can get clogged. Did you have the radiator flow tested? Just because coolant flows through a radiator doesn't mean it got through all the pathways needed for complete cooling.
Did you check the lower radiator hose. If that collapses under vacuum it will restrict the coolant flow through the radiator and can cause moderate to severe overheating. You shouldn't be able to squeeze the lower radiator hose closed with your fingers. If you can, then replace it.