No thermostat

[luk4mud]

Well, I'm still working my way through baselining projects as well as chasing an overheating issues. The two converged yesterday when I decided to change out the fan clutch and check the thermostat. There was no thermostat.

The PO had left the metal housing in place, but had cut out the sensor, spring and everything else.

Now I know that a bad thermostat can make a rig run hot, but could no thermostat do the same thing by not regulating the temp at all? There are some suggestions on the Man-A-Fre site that it could make 2 cylinders run hot and give a false (cooler) reading on the temp gauge. If that's the case and I have been running hotter than the temp gauge says, them I have other problems, like the radiator.

I'm gonna run it up a couple of big hills today and see how it does. If it's still running hot, then all I have left to check (I think) is:
Lower hose- some suggest it can collapse if its old
Radiator
Water pump?

Already checked/ done:
Thermostat
Coolant Flush
Fan clutch
Rad cap
Hydro blast of rad fins

Thanks for any help.

 

[turbocruiser]

The absence of a thermostat can cause overheating problems but most of the time the people that take those out are trying to solve some other overheating problem and they think that removing the thermostat will help when in reality it rarely helps. I would suggest you replace the thermostat but also be aware that other overheating problems are probably still present. HTH.

 

[Koffer]

I had this same thing when I got my fj60 no T stat . I installed a new Toyota T stat replaced the fan clutch as it was not working ,still had problems, replaced the leaking intake and exhaust manifold gasket as it was leaking , also thought it was having a vacuum leak making it run too lean
I pulled the Rad and had it flow tested , it was 80% blocked , replaced rad and everything fell into line .
The old fan clutch read bad since there was not enough water flow through it to heat the air enough to make it work .

Does it overheat while driving at speed ? but not idle then its most likely the rad is shot

You may also have a head gasket that's going south and blowing compression gasses into the cooling jacket too

 

[Tools R Us]

It is a bypass system, when the thermostat is closed, the coolant is routed back into the motor, when the thermostat opens the bypass is closed and coolant is routed through the radiator. If the thermostat is missing most of the coolant will take the path of least resistance, the bypass, little will go through the radiator. This type of system will always have less cooling capacity without a thermostat, and any cooling system diagnosis done without a thermostat has little/no value.

 

[AJP]

If the thermostat is missing most of the coolant will take the path of least resistance, the bypass, little will go through the radiator.

don't agree. If the thermostat is "punched" as luk4mud describes .. the path of least resistance is still through the radiator outlet hose and through the thermostat housing into the block. The problem is that it will likely hit the block at too low a temperature ... unless there are other problems (bad rad being the most likely one) and the engine will not reach the proper operating temp.
I have seen this sort of "fix" before .. the idea being that the thermostat flange (without the core sensor spring etc) will act to retard/slow flow enough so engine gets too proper operating temp. It is invariably done to try to "fix" a hot condition.. ... PO may have simply had a faulty thermostat and this was the expedient fix ... or other issues that you will have to watch for .. after replacing the thermostat

 

[Elbert]

simple logic.... if the OEM put a thermostat in the engine...it must be for a reason. Put one back in there....or plan to freeze your @$$ this winter. All in all there is no benefit on leaving the thermostat out of the vehicle.

When folks argue this.... simple question them as to why the OEM put the thermostat there in the first place... then go find a real mechanic and see what their thoughts are?

 

[jvazquez53]

Don't know but since is 85 degrees here all year around the thermostat removed does not makes a difference, however if you are in cold climate, it is a must!

 

[Tools R Us]

don't agree. If the thermostat is "punched" as luk4mud describes .. the path of least resistance is still through the radiator outlet hose and through the thermostat housing into the block. The problem is that it will likely hit the block at too low a temperature ... unless there are other problems (bad rad being the most likely one) and the engine will not reach the proper operating temp.
I have seen this sort of "fix" before .. the idea being that the thermostat flange (without the core sensor spring etc) will act to retard/slow flow enough so engine gets too proper operating temp. It is invariably done to try to "fix" a hot condition.. ... PO may have simply had a faulty thermostat and this was the expedient fix ... or other issues that you will have to watch for .. after replacing the thermostat

The pump pushes coolant into the block then it flows through the head, at the chamber in the front of the head it can flow two directions depending on thermostat position. If the thermostat is closed (bypass open) it flows back into the pump through the bypass line (red in the pic). If the thermostat is open (bypass closed), it flows out the far side of the head through the radiator and back to the thermostat housing (blue in the pic).

It can be argued that pumping through the several feet of necks, hoses, radiator is somehow less restrictive than ~6" of bypass, but that's not my experience. The bypass systems, without thermostats that I have worked on all warmed up slower (due to some flow going through the radiator) and overheated much easier (due to a large percentage of the coolant bypassing). They never had a fraction of the flow through the radiator as when the thermostat is working.

The "restriction trick" is to slow flow through the radiator and works on conventional/non bypass type systems. On a bypass system, if a restriction is put where the thermostat normally lives, it restricts the radiator flow, making it even more likely that a higher percentage of the coolant will flow through the bypass.

I'm a firm believer that all motors should have thermostats, they operate much more efficiently. If the thermostat must be removed on a bypass system, the bypass needs to be plugged or the cooling capacity will be greatly reduced, will overheat with much less load, ambient temp than one with a thermostat.

 

[turbocruiser]

Kevin, as almost always, is completely correct on this one.

To the OP, again, as long as any complete and correctly working thermostat is missing it is going to give you grief to diagnose the overall system BUT since it is missing I think that replacing it will confirm that something else specific is wrong with the system and that someone tried masking that problem through removing the thermostat. There are lots and lots of threads here to read through and as many fixes for as many failures of fans, gaskets and rads. HTH.

 

[AJP]

I disagree Kevin. BTW ... I read from luk4mud's op that the thermostat plate with the jiggle valve is there ... but the center (eg valve etc) has been removed

but had cut out the sensor, spring and everything else.

On a bypass system, if a restriction is put where the thermostat normally lives, it restricts the radiator flow, making it even more likely that a higher percentage of the coolant will flow through the bypass.

...since the thermostat valve - even when open - would represent a greater restriction then a thermostat with valve physically removed -- wouldn't it follow from your comment that all cruisers would have a significant overheating problem??


(BTW - let me add that there is some anecdotal evidence that having no thermostat installed can result in too high a temperature - the operating theory being that the increased flow leaves coolant in the rad for an insufficient time to properly cool....other theories are that the higher flow rate results in the main rad hoses collapsing - resulting in "pinching" off the flow of coolant - as a result some hoses are "reinforced" with steel coil to prevent collapse but ymmv)

 

[Tools R Us]

I disagree Kevin. BTW ... I read from luk4mud's op that the thermostat plate with the jiggle valve is there ... but the center (eg valve etc) has been removed ...since the thermostat valve - even when open - would represent a greater restriction then a thermostat with valve physically removed -- wouldn't it follow from your comment that all cruisers would have a significant overheating problem??


(BTW - let me add that there is some anecdotal evidence that having no thermostat installed can result in too high a temperature - the operating theory being that the increased flow leaves coolant in the rad for an insufficient time to properly cool....other theories are that the higher flow rate results in the main rad hoses collapsing - resulting in "pinching" off the flow of coolant - as a result some hoses are "reinforced" with steel coil to prevent collapse but ymmv)

The jiggle valve isn’t relevant, it’s only function is to allow any air trapped in the lower hose and water neck housing to more easily clear. The only time when it comes into play is when the system is first filled. Without the thermostat valves, it has no function, air will easily clear through the huge holes where the valves were.

The thermostat has two valves the are connected, operate at the same time. The front valve (blue in the pic) controls coolant flow to the radiator, the rear valve (red in the pic) controls the bypass flow. When the motor is cold most all of the coolant bypasses. As it warms there is a progressive mix of flow from both. When hot the bypass is closed and most all of the flow is through the radiator. It not about the restriction, it about the bypass being open, so how would a cruiser with a properly functioning thermostat have the same issue as one with the thermostat valves missing?

I agree that a restriction is necessary and that removing the valve isn’t enough. On competition motors that we built would make an alloy washer with a hole with about half the surface area as the thermostat hole. This only works on older cooling systems without a bypass circuit or if equipped the bypass blocked.

I don’t see how any of this trivia is relevant to the problem? See no benefit to running a cruiser without a thermostat, only negatives. Any cooling system testing done without a thermostat is irrelevant to a properly functioning system, so install a known good thermostat and find the problem.

 

[luk4mud]

Any cooling system testing done without a thermostat is irrelevant to a properly functioning system, so install a known good thermostat and find the problem.

Got a good one in now, and it still overheated coming up the hill to my house yesterday. So the quest continues.

This is great information, thanks for the cooling system primer.

 

[80t0ylc]

Got a good one in now, and it still overheated coming up the hill to my house yesterday. So the quest continues.

This is great information, thanks for the cooling system primer.

Reviving this thread for two reasons:

1. luk4mud, any update to your overheating blues?

2. Need some input on opinions on keeping thermostat out for cooling system cleaning.

Background: My original (AFAIK) 16 yr old thermostat started going out on me on an outing, this weekend. So, after ordering a new one at the local Mr. T store, I tore into the cooling system - 'bout time for a flush and change coolant anyway. I drained coolant and removed thermostat and it struck me - why not (while I'm waiting on the new one) button up housing and proceed with flush and cooling system cleaning with t-stat removed? I'm running some Prestone Super Radiator Cleaner with just water for a few days (parking indoors at night, of course). It needs 3-6 hrs of engine running time to work. This can be spread out over several days if necessary. I'm thinking with the t-stat removed, the water and radiator cleaner will move more freely throughout the system and have better results.

What say all you shade tree mechanics? Any feed back on this will be appreciated! Thanks!

 

[80t0ylc]

Bump-anyone?
Edit: should also mention that in the little drivng around that I've done so far, without t-stat, my RT modded temp gauge never gets above the bottom line. So don't know if this is such a good idea. It'll only drop off hi-speed idle after a run down the highway. Letting it sit and idle after that, the idle will slowly climb as the temp drops back down. Will running it for an extended period, say a couple hours, hurt the engine?

 

[Tools R Us]

...
2. Need some input on opinions on keeping thermostat out for cooling system cleaning.
... I'm thinking with the t-stat removed, the water and radiator cleaner will move more freely throughout the system and have better results.
...

I don't see the point? With the t-stat out the fluid will flow through both systems, so will have reduced velocity/flow in both.

... Will running it for an extended period, say a couple hours, hurt the engine?

As long as you watch it and don't overheat it, I don't see how it would be damaged.

As for the failure mode, if I had one fail on the trail, I would block it fully open and if it fell apart, then would plug/block the bypass and run it. In both cases it would run cold, full cooling mode, but much better than overheating, until a replacement was available.

 

[80t0ylc]

I don't see the point? With the t-stat out the fluid will flow through both systems, so will have reduced velocity/flow in both.



As long as you watch it and don't overheat it, I don't see how it would be damaged.

As for the failure mode, if I had one fail on the trail, I would block it fully open and if it fell apart, then would plug/block the bypass and run it. In both cases it would run cold, full cooling mode, but much better than overheating, until a replacement was available.

Thanks, Kevin. The t-stat did not fail completely. Just running higher temps than normal. When tested after removal, it has sluggish and incomplete movement. I think it's just tired after 16 yrs of service. Excellent performance for that time, though.

 

[80t0ylc]

Wow, I just spent the afternoon running with out the t-stat. Some highway driving, some city driving and even some very mild off roading, basically to check performance.

This 1FZ-FE engine is lost without the thermostat. I don't know how the OP or his PO got by for any length of time the way it was set up. Mine being completely out may have made it worse, but I can tell you - don't remove the 1FZ's thermostat to try and fix an overheating problem.

My experiment was for a different reason (as previously posted - to try and improve coolant system cleaning) and what I experienced was weird and spooky at times, but made more sense when you applied logic to it. I'm not exactly sure where the engines water temp sending unit is and also my temp gauge has the RT mod. Heater control = max heat. Weather was partly sunny, air temp 45-50*F.

Highway driving: Gauge stayed around bottom line. Drifted a needles width above going up grades and would drift below bottom line going down grades.

City driving and idling: 1-2 widths below bottom line and ECM set high speed idle 900-1100 rpm.

Off pavement, slow going is where it got weird: Temp gauge would drop down below bottom line, almost pegged. Idle would climb as high as 1500 rpm and it was cool to drop the t-case into Lo because I could just idle though minor ledges and rocks. But, I was climbing a hill and although the idle was set by the ECM at high speed, occasionally the fan clutch would kick in. When this happened, I stopped the truck, popped the hood to investigate. Temp gauge was fooling ECM. Quite a bit of heat was being created in the engine compartment which was causing fan clutch to kick in. Engine, radiator and hoses were much warmer, but temp gauge wasn't registering climb in temperature. This scared me, so no more slow speed hill climbing till I get the t-stat back in.

Anyway, I was being very cautious and I hope it is apparent from my screwing around that removing the t-stat can lead to problems that might not show up, till it's too late, even on a modified temp gauge.

 

[TomOsborne]

Well hey! So I'm here replacing the fan clutch, water pump, thermostat, etc. So what do I find? 2 things actually. 1) PO pulled the guts of the thermostat and I have the self made "restrictive" armature thing going on. So no thermostat sensor, but a framework from the old thermostat is still present in the water outlet. 2) The knowledge built into this message board is amazing. A whole thread dedicated to the theory of running without a thermostat, others encountering the same scenario from PO's, and people running without it for research. So bravo and thank you.

My overall cooling system is jacked. It doesn't overheat, or lose coolant, bit the heater lines are both chopped and just sitting there useless and there are caps at the water outlet redirecting flow and rendering the heaters useless. Which is not a big deal considering i live in FLA, and the PO bought this truck out of Miami..... But, I want to get it all fixed, flush the heater cores, and while i have the radiator out flush the hell out of it and maybe even take it somewhere to get it flow tested? Idk, but thanks everyone for the thread and let me know if you have any thoughts. Little sketched uncovering this but not surprised after some other stuff I have run up against.

 

[mudgudgeon]

Well hey! So I'm here replacing the fan clutch, water pump, thermostat, etc. So what do I find? 2 things actually. 1) PO pulled the guts of the thermostat and I have the self made "restrictive" armature thing going on. So no thermostat sensor, but a framework from the old thermostat is still present in the water outlet. 2) The knowledge built into this message board is amazing. A whole thread dedicated to the theory of running without a thermostat, others encountering the same scenario from PO's, and people running without it for research. So bravo and thank you.

My overall cooling system is jacked. It doesn't overheat, or lose coolant, bit the heater lines are both chopped and just sitting there useless and there are caps at the water outlet redirecting flow and rendering the heaters useless. Which is not a big deal considering i live in FLA, and the PO bought this truck out of Miami..... But, I want to get it all fixed, flush the heater cores, and while i have the radiator out flush the hell out of it and maybe even take it somewhere to get it flow tested? Idk, but thanks everyone for the thread and let me know if you have any thoughts. Little sketched uncovering this but not surprised after some other stuff I have run up against.

If heater lines are cut, i think you'd have a fairly safe bet that the heater core is leaking.