1988 743 bobcat overheating issue cant figure it out.

[Billybobjoe12323]

Hello all any help would be appreciated getting really frustrated lol.

I got the bobcat a few years ago from a guy and he said it ran on the hot side of things. I originally used it mostly in winter and didn't notice much other than the needle was about 3/4 way up instead of sitting verticle. Over the years and more recently I had to use it in the hotter months and it ran on the hot end but never crossed over the normal line. Eventually it started creeping up to hot so I figured I better check some things before it blows up.

I have replaced the rad cap and the belt for the water pump, I also flushed the rad out and put all new coolant in. I pressure washed the rad and oil cooler to get any crud out but surprisingly wasn't very dirty. The last thing I did was get a new thermostat for it but when I went to put it in there wasn't one. I figured that obviously wasn't going to help so installed the new one. Now when I run it, it runs about 15 or 20 minutes and blows the lid off the coolant overflow tank. Weird I thought so I tried taking the thermostat back out but it does the same thing.

I tried running it with the rad cap off and it blows coolant everywhere so I figured it was a head gasket issue blowing combustion air back into the coolant system or something. I bought a coolant pressure test kit and tested it. I put it up to 7 psi and it only dropped about half a psi after 30 minutes.

That seems like a very small pressure drop to me but wasn't sure if that was enough to indicate a head gasket issue? Is there anything else I cam check other than pull the head off?

 

[laurencen]

my first 743 had similar issues turned out a crack in the head, close between valves, did not notice at first so just changed the head gasket.

after taking it apart again and totally cleaning it up clearly a crack, it also did not leak down similar to yours

 

[Billybobjoe12323]

my first 743 had similar issues turned out a crack in the head, close between valves, did not notice at first so just changed the head gasket.

after taking it apart again and totally cleaning it up clearly a crack, it also did not leak down similar to yours

Oh really that's interesting, we're you able to have the head resurfaced and use it or do you need a new head when these Crack?

 

[laurencen]

it was junk, I tried peening and weld myself with no sucess, found a new stripped head on ebay and switched all the parts over

 

[Tazza]

These heads always crack when over heated, we rebuild this model engine, and if the engine has been over heated in the past, there is a very good chance the head is cracked.

 

[Billybobjoe12323]

These heads always crack when over heated, we rebuild this model engine, and if the engine has been over heated in the past, there is a very good chance the head is cracked.

Dang looks like I'll be pulling the head off then. Any tips or advice on the process or other thing to watch/ check for while it's apart?

 

[Billybobjoe12323]

it was junk, I tried peening and weld myself with no sucess, found a new stripped head on ebay and switched all the parts over

I was looking on ebay as well but was wondering how shipping charges would be with it being such a heavy item to ship.

 

[Tazza]

Parts to keep an eye out on these engines is if it's been cracked for a while, people run water and not coolant so welch plugs rust from the inside out. There are a few hidden ones, behind the front cover and one on the back behind the mounting plate.

We have had engines come in with water mixing with oil, a welch plug under the rocker cover failed.

Shipping depends on where you are i guess, freight around Australia for us generally isn't too bad.

 

[Micheal]

Is the motor and hydrostatic drive clean from dirt and oil buildup? This will keep the heat in and cause it to overheat. Also check the hydrostatic pressure relief valve and make sure is opening up when there is too high of pressure on the hydraulic system. This too will cause overheating.

 

[laurencen]

regardless of shipping costs it will easily be less than half from Bobcat

 

[Equipment_Tech]

Hello all any help would be appreciated getting really frustrated lol.

I got the bobcat a few years ago from a guy and he said it ran on the hot side of things. I originally used it mostly in winter and didn't notice much other than the needle was about 3/4 way up instead of sitting verticle. Over the years and more recently I had to use it in the hotter months and it ran on the hot end but never crossed over the normal line. Eventually it started creeping up to hot so I figured I better check some things before it blows up.

I have replaced the rad cap and the belt for the water pump, I also flushed the rad out and put all new coolant in. I pressure washed the rad and oil cooler to get any crud out but surprisingly wasn't very dirty. The last thing I did was get a new thermostat for it but when I went to put it in there wasn't one. I figured that obviously wasn't going to help so installed the new one. Now when I run it, it runs about 15 or 20 minutes and blows the lid off the coolant overflow tank. Weird I thought so I tried taking the thermostat back out but it does the same thing.

I tried running it with the rad cap off and it blows coolant everywhere so I figured it was a head gasket issue blowing combustion air back into the coolant system or something. I bought a coolant pressure test kit and tested it. I put it up to 7 psi and it only dropped about half a psi after 30 minutes.

That seems like a very small pressure drop to me but wasn't sure if that was enough to indicate a head gasket issue? Is there anything else I cam check other than pull the head off?

Sounds like Head gasket is cracked Head. Do compression test first

 

[Billybobjoe12323]

Is the motor and hydrostatic drive clean from dirt and oil buildup? This will keep the heat in and cause it to overheat. Also check the hydrostatic pressure relief valve and make sure is opening up when there is too high of pressure on the hydraulic system. This too will cause overheating.

The engine in clean but there is quite a bit of grime built up around the bottom of the engine. How would I go about testing the hydrostatic relief valve? Also where is it haha

 

[Billybobjoe12323]

Parts to keep an eye out on these engines is if it's been cracked for a while, people run water and not coolant so welch plugs rust from the inside out. There are a few hidden ones, behind the front cover and one on the back behind the mounting plate.

We have had engines come in with water mixing with oil, a welch plug under the rocker cover failed.

Shipping depends on where you are i guess, freight around Australia for us generally isn't too bad.

Interesting wouldn't have thought of that, thanks!

 

[Micheal]

The engine in clean but there is quite a bit of grime built up around the bottom of the engine. How would I go about testing the hydrostatic relief valve? Also where is it haha

On top back of the hydrostatic pump is a pressure switch with two wires going to it. One wire come from the wiring harness and the other goes over to the pressure relief valve, which is in the port block.

 

[Micheal]

I do not mean to offend!
I don't know everything and have a lot to learn but when I rebuilt mine I was having it run hot and my release valve wasn't wired up. When I did wire it up it started running cooler.
Just trying to help other fix their bobcats and pass on what I have learned from working on mine.

 

[laurencen]

with a 743 if it has ran hot the head is likely cracked, it will run hot, pressure the radiator never saw oil in the mix but its possible, compression test never shown up, the crack is small and hard to see but its there

pull the head and take to a shop to check if you can not find it, they can be had on ebay either complete or stripped and do not buy used unless its checked out

 

[walio123]

Guys, you can very easily check if there is exhaust gas in the antifreeze (damaged head or head gasket). Let me tell you a very simple method. You put a large funnel, so that it fits tightly into the neck of the radiator, add antifreeze up to 1/3 of the height of the funnel. You start the engine like this and wait for it to warm up /open the thermostat - which means that the upper hose becomes warm/. Antifreeze in the funnel will move, but if there are bubbles in it - then there are exhaust gases or part of the compression enters the antifreeze. Just be careful, because if the crack is big, hot liquid can splash on you. Of course, there are also chemical-based tests that change the color of the antifreeze if there are traces of gases inside. They are not expensive to buy, but they are not very accurate. It happened to me that I did not read gases in the antifreeze test, but in the funnel I see bubbles. That blow test you did will show you if there is a leak from hoses in the system - you can hear and see where the fluid is being lost.. With a cracked head, it usually doesn't work, because the cracks /if there are any/ expand when the engine warms up.

 

[Billybobjoe12323]

This is NOT a hy-stat problem. IF the oil cooler fan is not working the hy-stat oil can get too hot, yes, but that has nothing to do with the relief valve. Rarely rarely rarely rarely do you ever hit relief in the hy-stat circuit other than momentarily when you grab a lot of stick too quickly and almost kill the engine. To test the hy-stat relief you have to first engage the mechanical travel lock and then (slowly) pull in some control stick. IF the engine doesn't die the system will hit relief pressure and the relief valve will open. Do this in HIGH range only. If you do it in low range you risk breaking the mechanical travel lock.
You do NOT have a hy-stat problem. You have an engine over heat problem.
Venting of excessive coolant pressure (or blowing the cap off) indicates a cracked head or a cracked cylinder or a blown head gasket. But most likely a cracked head..

Thanks for your input!

 

[Billybobjoe12323]

Guys, you can very easily check if there is exhaust gas in the antifreeze (damaged head or head gasket). Let me tell you a very simple method. You put a large funnel, so that it fits tightly into the neck of the radiator, add antifreeze up to 1/3 of the height of the funnel. You start the engine like this and wait for it to warm up /open the thermostat - which means that the upper hose becomes warm/. Antifreeze in the funnel will move, but if there are bubbles in it - then there are exhaust gases or part of the compression enters the antifreeze. Just be careful, because if the crack is big, hot liquid can splash on you. Of course, there are also chemical-based tests that change the color of the antifreeze if there are traces of gases inside. They are not expensive to buy, but they are not very accurate. It happened to me that I did not read gases in the antifreeze test, but in the funnel I see bubbles. That blow test you did will show you if there is a leak from hoses in the system - you can hear and see where the fluid is being lost.. With a cracked head, it usually doesn't work, because the cracks /if there are any/ expand when the engine warms up.

Ah that makes sence! Was wondering why the psi wasn't dropping more.

 

[Jim A]

Put a rubber glove over radiator neck . If it inflates while running it's combustion gas in coolant .
Auto parts has a chemical test kit to sample coolant test for such for $30 .
But bubbles in coolant and rubber glove test cost nothing.