Cavitation? Water pump? Thermostat L20B

[rt5nine]

Having some weird temparture reading on the truck. To start I have a L20B in my 74 620. It seams to run a little warm when in normal city driving. When I'm on the freeway it runs hot 230ish. I replaced the tstat this weekend and now my temp gauge is going crazy. From 160 to 230 and back down again within a couple of blocks of driving.

Has anyone ever had something simuliar happen? I thought maybe its cavitation of my water pump.

Thanks in advance for any help

[datsunaholic]

Thermostat bounce? I've seen that with cheapo modern thermostats.

[MicroMachinery]

Did you bleed the system of all the air after you replaced the thermostat?

[datzenmike]

Replace the thermostat. Get a $12 one. You must have an after market gauge to know the temp it went to. That gauge or it's sender reliable???

 

 

Cavitation bubbles are actually not air but vacuum gaps caused because the water cannot move fast enough to fill in the space behind a rapidly moving propeller. The real problem is that they eventually collapse with great force and this 'erodes' metal.

[Sealik]

When you installed the thermostat...was the jigger positioned away from the engine?

[rt5nine]

Replace the thermostat. Get a $12 one. You must have an after market gauge to know the temp it went to. That gauge or it's sender reliable???

 

 

Cavitation bubbles are actually not air but vacuum gaps caused because the water cannot move fast enough to fill in the space behind a rapidly moving propeller. The real problem is that they eventually collapse with great force and this 'erodes' metal.

 

I'm fairly sure the after market gauges are accurate, been in the truck for 2 engine swaps. MicroMachinery asked if I bleed the air out? How do you do that? It does sorta of seams like vapor lock.

[RoadRace]

I'm fairly sure the after market gauges are accurate, been in the truck for 2 engine swaps. MicroMachinery asked if I bleed the air out? How do you do that? It does sorta of seams like vapor lock.

 

re: bleeding or getting the air out - in the industry its also known as de-aeration. anyway, there are a couple ways to do it. tried and true way for me is:

 

1) take stat out and fill up the engine through the stat hole.

2) jack up the front of the car and top it up.

3) drill a 1/8" hole on the flat part of the stat that will allow minimal air and coolant to pass through.

4) put the stat back in and the hose back on.

5) with the front of the car still in the air, fill up the rad to the top.

6) lower the car.

7) start the car and watch the fluid level; if there were any air pockets, they should become evident as the fluid level will drop as seen looking down in the rad tank with the cap off.

 

if the coolant stays at the same level after the car is at temp and the stat has opened, then:

 

8) rev it up to 2500 rpm and watch the coolant level drop, add coolant

9) put the rad cap back on with the engine still running high

10) drop the throttle, shut the car off.

 

done.

 

PS: vapor lock is fuel related.

[Hoosier77]

only 2 people know about cavitation, that would be HIANZ, and your DENTIST :lol:

[rt5nine]

re: bleeding or getting the air out - in the industry its also known as de-aeration. anyway, there are a couple ways to do it. tried and true way for me is:

 

1) take stat out and fill up the engine through the stat hole.

2) jack up the front of the car and top it up.

3) drill a 1/8" hole on the flat part of the stat that will allow minimal air and coolant to pass through.

4) put the stat back in and the hose back on.

5) with the front of the car still in the air, fill up the rad to the top.

6) lower the car.

7) start the car and watch the fluid level; if there were any air pockets, they should become evident as the fluid level will drop as seen looking down in the rad tank with the cap off.

 

if the coolant stays at the same level after the car is at temp and the stat has opened, then:

 

8) rev it up to 2500 rpm and watch the coolant level drop, add coolant

9) put the rad cap back on with the engine still running high

10) drop the throttle, shut the car off.

 

done.

 

PS: vapor lock is fuel related.

 

Cool I will give this try. Thanks for the help!

[Sealik]

When you installed the thermostat...was the jigger positioned away from the engine?

 

And...?

 

re: bleeding or getting the air out - in the industry its also known as de-aeration. anyway, there are a couple ways to do it. tried and true way for me is:

 

1) take stat out and fill up the engine through the stat hole.

2) jack up the front of the car and top it up.

3) drill a 1/8" hole on the flat part of the stat that will allow minimal air and coolant to pass through.

4) put the stat back in and the hose back on.

5) with the front of the car still in the air, fill up the rad to the top.

6) lower the car.

7) start the car and watch the fluid level; if there were any air pockets, they should become evident as the fluid level will drop as seen looking down in the rad tank with the cap off.

 

if the coolant stays at the same level after the car is at temp and the stat has opened, then:

 

8) rev it up to 2500 rpm and watch the coolant level drop, add coolant

9) put the rad cap back on with the engine still running high

10) drop the throttle, shut the car off.

 

done.

 

PS: vapor lock is fuel related.

 

 

2 holes in "stat"....jigger included?

[banzai510(hainz)]

I drill a 1/8 hole in top of stat to help with the airbubbles and a smooth temp rise.Early 521s and 510 had a bypass on the stat housing already to the intake water line.

I dont know if this is recommended or not but it works for me.

[rt5nine]

The temp gauge is holding right at 185ish. Think i'm good, though its seams I keep seeing white puffs of smoke. Hmmm maybe head gasket?

[banzai510(hainz)]

coule be wore out intake manifold gasket or loose intake bots to the head. if your head has a water passages the water could get sucked in