Hey guys, I have an 86’ samurai with an 8v tracker motor. The thing has always tended to run hot/borderline overheat when driving 4wd on the sand and going uphill. The water pump recently failed, and I replaced the pump, timing belt, thermostat, and reset the valve lash and timing. The motor sounds better than ever now, but it still has the same overheating issue. Just to try it, I took the thermostat out, and drove it around and it never started overheating. The motor temp actually stayed right between 180-210 the whole time, even climbing uphill for a while. I’m thinking the radiator or fan clutch might not be working 100%, but I was wondering if there is a serious downside to running without a thermostat if the motor temp is still getting hot enough? Also, if a brand new thermostat is working properly, why would it be less efficient at cooling the motor than no thermostat? Less restriction on the flow of coolant?

Thanks for looking

‘86 samurai tracker swap - 1.6 8v

Running a motor without a thermostat is a VERY BAD IDEA - for starters, it will take longer to reach operating temperature - it will also burn more fuel (because it takes longer to reach operating temperature) and wear faster (because it takes longer to reach operating temperature.

If it runs at the right temperature without the thermostat your problem is not the fan clutch, but a coolant circulation issue, possibly a partially clogged radiator

I second flow restriction somewhere.  When you couple reduced flow with the restriction of the thermostat, it causes a problem...how quickly is the motor getting up to temperature?

Thanks for the responses. I was not really planning on running without a thermostat as a permanent solution. I’m just trying to figure out what needs to be replaced. The thermostat is not very old, but there is also no mud guard, and it may have gotten dirty. With a 180F thermostat in, the engine warms up above 180F within 2-3 minutes, and after idling down to 900rpm the idle temp is 200-210F. Without the thermostat, it warms up to 180F after about 5 minutes of driving around. When I drive around on flat roads it stays right at about 180F with no thermostat in. The gauge is an aftermarket, not the original, but I also ordered an IR gun to make sure it’s actually giving the right temp. I think I’m just going to replace the radiator, and the fan clutch look really old so might as well just do the full job while it’s apart.

I wouldn’t consider 210 overheating.  That is not uncommon our high for later model fuel injected vehicles.

More out of curiosity than anything else - where is the temperature sensor for the after market gauge installed?  Do you still have the factory gauge fitted, if you do, what does that indicate?

There is a reason the factory gauges don't have numbers, and are also "non-linear" - they will indicate a "normal" temperature over a fairly wide range of variation - it's done to prevent people from becoming overly anxious because they feel the temperature is higher than it should be.

212*F is generally accepted as the boiling point of water, but that is when it's at atmospheric pressure at sea level - automotive cooling systems are pressurized to allow them to operate at temperatures higher than boiling point, with a 13 psi pressure cap, the boiling point is going to be in excess of 240*F - looking at the FSM for the G16b engine when fitted to a GV (it's what I have to hand), the stock thermostat starts to open at 190* +/- 3.5* and won't be fully open until 212* - that suggests that not only is 212* not a cause for concern, but your 180* may be colder than desired.,

210 was just at idle. Going uphill and 4wd on the sand it climbs to 240+ pretty quick with the thermostat in. The dash gauge doesn’t read anything, and I had assumed the aftermarket gauge was wired into the line that went to the dash gauge. The aftermarket gauge was installed before I bought the car. I’m just waiting for the IR gun to arrive before I start to overthink the problem.

If the aftermarket gauge is in fact wired to the original sender that would be cause for concern - the gauge has to be matched to the sender for it to read properly (accurately) and the OE gauge sender is not designed to provide that level of resolution.

I use an OBD2 reader (mine blue tooth's to my phone), and it give me a digital read from the computer.  Now I know where 200 degrees is on the stock gauge.  When I was running a non stock gauge on my dash, I taped another sending unit into the output housing and ran that for my gauge feed, so the stock sending unit was going to the computer without interference.

My motor , with a 180 thermostat, idles at 180 degrees for a long time before the temperature starts inching up.  My electric cooling fan (I don't have room for a mechanical fan) is on a 200 degree switch, and when the fan comes on it will cool right back down to the 180 degree and shut off.  (The stock electric AC booster fan is not sufficient as an engine cooling fan without the mechanical fan support.)  I am also running an inline temperature switch on my transmission output line to the cooler set at 180-165, that will also activate my cooling fan that covers most of the trans cooler also.  Now if my transmission starts getting hot my fan starts and cools both transmission and motor.  Tfhe motor won't run any colder because the thermostat will regulate the motor temperature.