The recent (Feb 07) thread regarding the operation and range of the XR4Ti's stock temperature gauge brought me to the realization that we didn't have a FAQ on this frequently asked question. Now is your chance to share facts and experience with the community on the topic. After the thread dies down it will be moved to the FAQ section to keep this forever. Errors will be edited as necessary.
The stock temperature gauge often reads low in some XR4Tis (typically the early ones). It is not unusual for the gauge to read right at or slightly above the bottom hash mark when at full operating temperature. Apparently, the gauge sender and the gauge didn't have matching ranges. A later gauge sender, often referred to as the "purple ring" temperature sender, usually rectifies the problem.
The purple ring sender:
(Can you guess why it is called "purple ring?")
The gauge sender is in the lower intake manifold. More specifically, it is in the brass tee fitting coming out of the lower intake. (Can someone fact check that sentence. I haven't touched a Merkur in a while and my brain might be failing me.) A single wire connects to it which is held in place by friction and the tension of the electrical connector.
Can anyone help with the hex size of the fitting? I don't have a sender in southwest Asia with me to check it out myself.
Naturally, there is more than one possibility for a gauge that reads low. I've seen lower intakes that were heavily clogged with the copper from radiator leak stopping additives. Complete lack of coolant flow past the gauge sender can extraordinary effects on gauge accuracy (among other problems). As the wiring ages the increased resistence of the wire can also cause gauge accuracy problems.DPDISXR4Ti wrote:All fittings are 3/8" NPT. The hex on the sender requires a 5/8" wrench or socket.
Replacement is fairly easy and can be done without fiddling with a bunch of stuff. I've found that I can get the old one out and the new one in without having to drain the cooling system. Yes, some coolant flows out of the opening with the gauge sender out of the manifold. If it doesn't leak then you have a clog that needs to be addressed. Don't use teflon tape on the sender. It has a thread sealant on it that allows the sender to maintain its ground with the engine block.
The clogging problem in the lower intake and around the gauge sender is reason to never use the leak stopping additive to the XR4Ti cooling system. It'll clog your heater core too.
My personal preference is to install a quality aftermarket gauge in order to get a numerical value to the coolant temperature, rather than a range that we don't know the actual scale to. This has been done to the racer and will be done to my road car.
That's all I can think of right now. Please post and add your knowledge.