How hot is hot? Installing actual gauges | Project Toyota MR2 Turbo

Update by J.G. Pasterjak to the Toyota MR2 Turbo project car
Jun 10, 2022

Since we’re planning on some on-track excitement for our 1991 Toyota MR2 Turbo this summer, monitoring engine functions is going to be a priority.

Unfortunately, the only indicator we have on the factory dash is engine temperature, and that gauge only indicates the temperature as “line” or occasionally “other line.”

Of particular interest to us was oil temperature and oil pressure, as our fourth-generation 3SGTE engine only holds four quarts of oil, and we were curious how hard it was being worked.

Our solution came from Summit Racing and their house lineup of electrical gauges. We ordered electrical oil temp, oil pressure and water temperature gauges, all of which came with their own sending units threaded with 1/8 NPT threads.

So the trick would be to adapt those 1/8 NPT threads to our MR2, whose engine was mostly equipped with ports threaded in BSP pitch. Because of course they are.

Luckily the aftermarket has our back, and the 3SGTE engine also has some convenient ports to access your vital fluids. For oil, there are a couple of options.

Racer X Fabrication sells a trick little oil adapter block featuring a nipple that threads into the head, back where the stock oil pressure sensor lives.

This block then has two ports, one threaded in 1/8 BSP for the stock oil pressure sensor and the other threaded in 1/8 NPT for an aftermarket sensor.

This was our original plan, and it would have worked, too, if it weren’t for you meddling kids. The meddling kids, in this case, were whoever built our engine harness for the Gen4 swap. Not that they did anything wrong–to the contrary, they did an excellent job–but the wire going to the stock oil sensor was just long enough to reach the stock location and didn’t have enough slack to reach the sensor once it was relocated by the block. We could have simply extended the harness, but we had another option as well.

Located right above the oil filter are three 3/8 BSP plugs going directly into the oil passages. Using some 3/8 BSP male to 1/8 NPT female adapters we used two of these ports to use for our oil pressure and temp sensors. Eventually we’ll extend our harness to work with the Racer X block–we don’t love the fact that one of the sensors is kind of close to the spinning crank pulley–but for initial testing it’ll work just fine.

Installing these adapters required draining the engine oil, so we used this opportunity to change the filter while refilling the sump with some Motul Classic Eighties 10W-40, a semi-synthetic from its lineup specifically engineered for ’80s and ’90s cars.

[Special oils for ’80s and ’90s classics | Motul introduces lineup for the Radwood era]

Motul recommended its ’80s 10W-40 rather than the ’90s 10W-30 for our MR2, and the additional viscosity and increased zinc of the 10W-40 should pair well with our old-school turbo engine.

For water temperature, we used a 28mm Mishimoto coolant hose adapter with a 1/8 NPT port placed in the coolant line that sits right above the thermostat in the system.

It’s a very accessible line, but doesn’t give you much indication of what’s going on until the thermostat opens, which was kind of dumb on our part. Would it be that this was the first time we had done something dumb, we may actually feel bad about it.

After a few eye rolls, we moved the sensor to one of the main radiator hoses that’s always wet and lives in a spot in the system that sees coolant at a temperature more indicative of what’s actually coming out of the engine.

Our temperature gauges were mounted in a fill panel that took the place of the double DIN radio–long since removed as the car sees more and more “fun” duties, and the oil pressure gauge shares an Autometer A-pillar pod with the boost gauge.

So now we know a few things, like the fact that the engine coolant temp stays pretty reasonable, rarely getting above about 220 degrees, even after a few hot laps in 90-degree heat.

Oil pressure stays fine on track as well–supposedly the Gen4 3SGTE has decent baffling in the pan. Oil temperatures can occasionally exceed 250 degrees, however, so a small oil cooler may be in order, as Florida is Florida, and even track days in November can see temps in the high 80s or low 90s.

But, still, way better than “line.”

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