Did you bleed the system with the thermostat out?
You are describing a no water circulation in the motor which is why the fan isn’t coming on when it gets to that point in temperature. The most common problem is air in the cooling system from a blown head gasket. If the lower hose doesn’t get hot than the thermostat never opened and the fan will not come on. If it is other than air you have an uncommon problem such as the water pump impeller broken, Rad. Completely clogged, or something clogged. With running straight water you can have parts fail prematurely.

 

Thank you Chris.

I think i bled the air but do not rmember for sure since i did that quite a few times today. Will check that in the morning.

I am thinking a clog or the H2O pump. Is it correct to assume that the inside of the engine has water ways that are far larger then the radiator? Any way to check the H2O pump w/o pulling it?

Other things i am thinking to try right now is to drain the fluid and try to blow air up thru the lower hose to see what kind of flow i get. Also thought about trying to firce water up the lower hose to again check flow.

Thanks again for the help.

 

You mentioned running straight water & it drained out brown. RUST. Antifreeze has corrosion inhibitors & without that you have stuff rusting within hours.

You can check for clogged radiator by disconnecting both hoses. (I usually unbolt T-stat housing because it's a pain to undo the hoseclamp at the bottom of the radiator.) Use a garden hose to flow water through the radiator - it should flow easily through even with a normal household garden hose at full blast. Flush it in both directions to remove any loose crud.

With the T-stat opened up, you can do about the same thing with the engine. Flush the water into the T-stat housing & watch it come gushing out the nozzle for the upper radiator hose. During this, the heater temperature control should be set all the way to HOT.

If you have hot water in the garden hose, all the better.

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You mentioned the fan doesn't run when it's overheating. There's a fan switch in the T-stat housing, that one's responsible for the fan while the engine is running. Unplug that & jumper the wire with a paperclip. Key on, that should make the fan run (both fans I think). If it DOES, then replace that fan switch.

 

Jim,

When i jumper that fan connector at the T-stat both fans come on. Sounds like a bad switch.

Will flush with water this morning and see what i get. Sure hope it's a plugged radiator as i do not really want to do the H2O pump again.

 

Disconnected the T-stat housing and the upper radiator hose. Flushed the radiator from the top and bottom. Good flow and only slightly brown water came out. No chunks and no flow restriction at full hose pressure.

Flushed the engine from the upper radiator hose. Water coming out of the T-stat housing was againn slightly brown and unrestricted. Tried to flush engine from the t-stat housing but most of the water came right back out. A little came out the upper radiator hose. Figure that was mostly because i could not get a good seal on the t-stat housing with the hose.

So..... Seams like my choices are:

1. a potentially bad t-stat housing thermal switch. Will that alone cause overheating?
2. a bad H2O pump. Would one break in 9 months running straight water? Is there a way to test it before i pull it?
3. Some other obscure problem.

What would you do next?

Thanks

 

Sounds like you have good flow through tne engine & radiator. I understand about it just splashing back out when you try to put it into the T-stat housing. Last time I did that was summertime & I ended up soaking wet.

1) When you drive even 10mph, there's plenty of air through the radiator so the fan doesn't need to run. That will only cause overheating when parked & idling.

2) I've never known anyone to run straight water that long. Corrosion doesn't take long at all, if the conditions are right. There aren't many iron things in the cooling system, so the waterpump impeller probably is the source of the rust you saw. Wish I knew a better answer...

3) Bad thermostat. Fairly new, right? They've been known to be bad right out of the box, but not all that often.

 

Jim,

Thermostat is new. Bought it yesterday. It is aftermarket but i tested it in boiling water.

Pulled and tested the t-stat thermalswitch. In cold water it shows open. At about the point my water goes to a full rolling boil the switch will close but not show true 0 ohms. (-.67 is what i got) I figure that probably does not matter. Moved it from hot to cold water and it woudl open and close consistantly. I figure it is good but why don't the fans come on? Again if i short out the t-stat thermoswitch switch connector both fans run.

I did clean some crud off of the thermoswitch so maybe that was the problem.

Seams like i need to verify flow on the H2O pump. If i leave the t-stat housing off, fill the engine with water and turn it on for a few seconds it seams like i should see good flow. Will try that next.

 

It's supposed to close the circuit at 190F or something like that (wish I knew the actual number). If it takes a rolling boil to close the switch, that's already overheated. The difference between zero ohms & +1 or -1 is within the measurement uncertainty of most normal mortal multi-meters.

With the T-stat housing open, you can probably see more than one passageway leading into the engine. Try to squirt the hose into each one & check.

Don't run it with the T-stat housing open. Instead, bolt the housing closed without installing the thermostat. Fill it up. NOW you should be able to see motion in the radiator. It's not wild high-speed flow, unless you grab the throttle cable & rev the engine.

 

Ok, not sure if this is a good test but...

Left t-stat housing off. Jumpered the ground wire from the housing back to the motor so i could start the car. Left the radiator cap off. Rest of hoses are connected normally. Filled radiator so the engine was full of water.

Started the car. Left the hose running to fill the radiator as water left the engine. I was expecting to see a surge of H2O from the engine side of the t-stat. Nothing. lots of water out the radiator side of the t-stat housing.

So, without total understanding of what the flow should be out of the engine it seams like i am not pumping water. The water that did come out of the radiator side was just overflow and no real forced flow from the engine.

To me that sounds like my pump is gone. does this sound reasonable? Also, i really have not had ongoing temp issues. This sort of just jumped on me so it seams like the pump broke instead of something going bad over time.

Please advise if this sounds solid as i really am not looking forward to doing the pump.

Thanks

 

Jim,

Saw your post after i posted my latest test. I will put it back together w/o the t-stat and check for flow in the top of the radiator. Will report back.

The dealer does not have any thermoswitchs in stock but it sounds like since i overheat at low spead that this is not my primary problem. I overheat at idle or at speed. I can probably drive 2 blocks before i overheat.

More testing....