1988 90 v8 3.5 - temperature

[Mediamab]

So I have ensured coolant all topped up and running through the system which is all working well. Thermostat appears to be kicking in when engine gets warm but idle the temp gauge barely hits the white area, even when running only goes slightly into that white area and nowhere near the middle. I’ve checked the gauge by earthing the sender wire and it tops out so it’s working fine. Would this suggest I need to replace the temp sender? The engine definitely is very hot, as coolant pipe I can’t hold for long once up to temp.

[Escape]

Are you using the original sender and gauge? If not, are you sure they are matched? Additional resistance in the wiring, for example due to a bad connection, will also cause a low reading. 

If you are sure the thermostat is opening, the temperature will be in the normal range and should show so on the gauge. You can use an external thermometer to check, or even better take out the sender and put it in a kettle with a thermometer to check the readings.

[Mediamab]

To be honest I have no idea if they’re original or not as only had the truck a month. How do I ensure they are matched?

ill give the sender a test at some point and see if that sheds any light.

i assume I’m right to be expecting the gauge to be in the middle?

[FridgeFreezer]

Has it ever had an engine swap for example? The gauges are matched to the senders, so a TDi gauge with a V8 sender will read totally wrong.

You can use a £5.99 multimeter to test the sender resistance in ohms, I think at this age they even put the numbers in the service manual so you can look it up - if not they're bound to be on the internet.

The gauge should sit in the middle, sometimes folks like to put "cooler" thermostats in because they think that's a good idea or to "solve" overheating - it *should* most likely have an 88 degree stat in it but 74 are a common mod, that would prevent it ever warming up properly.

[Mediamab]

It hasn’t had an engine swap but it does have an eidlebrock carb and I asssume sender could have been changed at that point and fitted into the manifold then?

I’ll give the sender some tests and see if that’s the issue. If not I guess changing the thermostat, or checking what type it is would be good

[FridgeFreezer]

TBH if I was going as far as removing the stat to take a look I'd be fitting a good quality new stat anyway for the £10 it's going to cost. Just make sure it's got the vent hole / bypass in it and it's fitted with the hole at the top.

[Mediamab]

Good shout, I’ll try and find the right sensor for the carb manifold

[FridgeFreezer]

2 minutes ago, Mediamab said:

Good shout, I’ll try and find the right sensor for the carb manifold

You need the right sensor for whatever your gauge is, which may not be the same as whatever fits the Edelbrock manifold... I got bored of playing that game and bought a VDO Vision gauge & sender, gives me a temperature in degrees and I know the sender & gauge are matched. Just need to work out the thread in your manifold.

[Mediamab]

Yeah I had saved the below the other day after doing quite a lot of digging which seems to be correct for the engine and manifold thread from what I could tell! 
https://rimmerbros.com/Item--i-PRC2506P

[smallfry]

Although the engine may feel very hot, it might not even have a thermostat in it. I have had many of the engines through my hands where it had been removed.

I can't remember now if the V8 90/110s had "Otter" switch as a temp sender on the top of the manifold. Held in by three screws. That was certainly different than the later types.

[Mediamab]

I assume if it was removed though then I’d see the coolant starting to heat from engine start? As it definitely kicks in after a period of engine running?

the sender is definitely just screwed in - pic attached