engine temperature

[dansalisbury72]

Issue: My temp gauge does not work properly and I am looking for a way to ensure that my engine is not overheating.

Background: after anywhere from 5-10 minutes of driving my temp gauge goes from the bottom of the range on the gauge to the top with no stops in between. I have replaced the temp sending unit that screws into the motor and still have the same problem with the gauge.

My proposed solution: I borrowed a laser temp gauge but am not sure what surface temp would tell me that it is normal temp or if it is indeed getting too hot.

My question: what locations and what temps would give me the best assessment of whether the motor is overheating? I already took a couple shots around the engine and most places are in the 140-160F range (after about a 15-20 minutes drive and with the temp indicator at the very top of the gauge), except for the cylinder head (taken from the driver's side of the head) which ranged from 190-215F.

Any help would be appreciated...

thanks...

Dan

[SafeAirOne]

Dan,

{edit}: Are you trying to figure out if you do, in fact, have an overheating issue, or are you trying to work around having an operating gauge for a while? If you are trying to verify an overheating issue, I'd just go down to my local auto parts store and buy a cheapo capilary-type generic temp gauge and the appropriate adapters to thread it into the port that your sender is now threaded into, then run it and see what the water temp is. You don't have to mount the gauge, just run it out to the top of the bonnet and tape it down where you can see it while driving.

If you are trying to work around having an operating temp gauge, then: {end edit}

Does your fuel gauge also give erroneous readings after 5-10 minutes?


All-in-all the temp circuit is fairly simple--12v comes off the fuse thats hot in the "run" position, gets convreted to 10-ish volts at the voltage stabilizer, then goes through the gauge and out through the temp transducer (sender) to ground.

Any faulty readings on the fuel gage would mean an issue with the light green wire, the voltage stabilizer or the green wire.

If the Fuel gauge is OK, then your problem is with the gauge, the light green w/blue wire or the sender.

[scott]

do y know which thermostat ya got? i'm using an aftermarket temp gauge/sender and it's reading 160. your temp and fuel gauge are power through a volt stabilizer and if it goes bad both gauges will read wrong.

[dansalisbury72]

thanks for the replies...

first off, I want to make sure that it isn't overheating, that is why I wanted to shoot a couple locations around the motor to see if anything is running hot (from the outside anyway).

The thermostat in it is one I got from Rovers North.

The fuel gauge works fine - no issues there.

[Nium]

Start with the engine cold. If you open the radiator cap after the engine is warm an explosive release of hot engine coolant will be released from under the radiator cap. By keeping the cap off with the engine cold and then bringing the engine to operating temp the coolant won't build up pressure and there won't be an explosive release of hot coolant. It would be a good idea to jack up the front of the rig and put it on jack stands so any air bubbles would migrate to the open radiator.
Remove the radiator cap
Place a meat thermometer or candy thermometer into the top of the radiator in the radiator cap hole
Start the engine and idle till the upper radiator hose is hot, meaning the thermostat is at operating temperature and therefor the engine too.
Check the reading on the thermometer you have in the radiator cap hole. Now you know what temperature the engine is running at.

Check the voltage stabilizer to make sure the wire to the temp gauge is on the same side as the fuel gauge. One side of the voltage stabilizer is 12V input and the other side is 10V output but both sides have two male terminals.

Cheers

[dansalisbury72]

I actually tried that a while back when I first started trouble shooting the issue and the engine temp was pretty low - around 110F if I remember correctly (caused a bit of drama because I used my wife's baking thermometer and she was not happy with that). Then I pulled the thermostat housing and discovered that there was no thermostat in there, thus the low temps. I have since installed a RN thermstat and will try it again.

Normal operating temperature is around 180-190-ish, correct? I think up around 200F+ is approaching the hot side, correct?

Again, thanks for the notes guys, much appreciated...

Dan

[dansalisbury72]

alright, just went out and did some work on the truck and a couple things happened, one bad and one possibly promising...

1. the bad - I did as instructed above to check the coolant temp - opened the radiator cap and started the truck and stuck the wife's baking thermometer in the coolant (have done this before with no issues). waited and waited for the thermostat to open and no dice (the upper coolant tube never got warm), so I decided to shut it down and move the operation outside. Went and turned off the ignition and coolant blew out of the radiator all over the place. rookie mistake or did I screw something up? Like I mentioned I have done this a couple times before and coolant never shot out when I shut the truck down.

2. the promising - while the truck was idling (and the temp gauge in the truck hit max temp) I decided to see what would happen if I disconnected the wire that connects to the water temperature transmitter (part number 36 in my engine parts manual). disconnecting this did not affect the gauge in the cabin - it still stayed at the hottest temp. Then I disconnected the wire going to the thermostat switch (aka 'the choke light' in my manual - part numer 29 on the engine sketch) and the temp gauge in the cabin went cold, telling me that this wire is what is connected to the temp gauge in the cabin.

I have never messed with electrical stuff prior to this truck and quite possibly have wrongly assumed this whole time that the water temperature transmitter was the part that dictated whether the temp gauge in the cabin read the proper coolant temperature. Or these two connections were just switched up. There is a green wire that currently connects to the thermostat switch that disappears in a wiring harness, but I can tell that it does not lead over to the voltage regulator.

hopefully this is not as confusing to read as it has been to write. Send help this way if you can...

thanks...

Dan

[dansalisbury72]

after I sent the last rambling email and took a trip to the store to pick up some more dri-sweep for the coolant that was all over my garage floor I came back and simply switched the two connections I mentioned in the last note and it seems to have fixed my problem (who would have thought that it would be something as simple as that?). The temp gauge seems to be working properly now - although it rode right on the Normal/Hot border for quite some time before the thermostat finally opened.

now onto the leaking hub seals...

[Jeff Aronson]

I can't help you on the wiring of your temp gauge, because I have one of the older capillary gauges on my II-A, and I'm unfamiliar with the wiring of a temp gauge. The sending unit, usually screwed into the side of the thermostat housing, would not logically send current directly to an electric gauge, however. The unit might be fine but the gauge itself might be wired incorrectly, or have a faulty component. The diagnostic advice given by others here makes sense in terms of tracking down any potential electrical problem.

When you start your car with no radiator cap, it will not rise to full operating temperature because the system was designed to be pressurized - thus allowing for increased operating temperatures without boiling the coolant mixture.

In general, thermostats do not open - allow for circulation to cool the engine - until the coolant temperature rises to either 160 F or 180 F [so called summer or winter thermostats].

The fact that you moved the car, circulating more water and building up greatere internal pressure in the block, thus resulting in the "shooting out." I assume you didn't move the Rover very far, but if you revved the engine to move it, and then shut it off quickly, I can see a full radiator spilliing over.

When a car is overheating, you'll experience common engine symptoms of running too hot. When you shut the car off, it will "diesel" or continue chugging with the ignition off. The engine might "knock" or "ping" when it's under load, such as accelerating up a hill in a higher gear. You will likely get boiling or bubbling in the coolant reservoir alongside the radiator. There might not be any difference in temperature between the top and bottom of the radiator, in other words, as if there's no effective cooling going on because the running temperature is just too high.

And lastly, the Land Rover Series radiators are quite big in terms of capacity for the engine. The nearly 8 quarts of oil in the engine also absorbs a lot of heat. Idling your car in the winter, even in North Carolina, won't necessarily warm it up very much. Without a cap on the radiator, it can take a while to get the engine to warm up. So perhaps the low temperatures are not that surprising.

As an aside, a quick look online suggests engine temperatures for water-cooled cars without significant emissions equipment run between 200 -250 degrees F. Note that engine paint is formulated for temperatures up to 500 degrees F.

Let us know what you uncover in your diagnostics.

Jeff

[jac04]

The sending unit, usually screwed into the side of the thermostat housing, would not logically send current directly to an electric gauge, however.
Not sure I understand what you are trying to say here. The sending unit is in the head. Why wouldn't it be connected directly to the electric gauge? It is obviously directly in the water temp circuit.


Anyhow...

Dan-
Your original problem sounds exactly like the temp sender and the cold start warning switch were reversed. As soon as the engine warmed up, the cold start switch made the circuit, and the gauge went from cold to full hot. Now that they are reversed, everything seems to work fine. Most gauges I have seen have read toward the top of the 'normal' range, so I think you are OK.

[dansalisbury72]

Jeff -
I didn't actually move the truck - it was still sitting in the garage and as soon as I shut it off I heard the coolant gush out - that's why it didn't make sense to me (but I know not to do it again).

Anyway, yeah, the water temp transmitter is in the head and after checking the wiring diagram in my manual supplement - looks like it does indeed go straight to the gauge then to the voltage regulator. Probably should have checked that out before I started this little project.

Appreciate all the info and advice guys, thanks...

Dan

[Nium]

Sorry you got a geyser of coolant Dan. I've done the procedure before and haven't gotten a geyser of coolant when shutting the engine off either. It was a procedure I learned from a mechanic I had worked for years ago. :o