77RogueRunner

I pose this question because I have been scratching my head over a few cooling/gauge issues lately. Let me begin by stating that I have a 03 3.4 in an 88 Runner with the SR5 cluster. The engine and radiator upper seemed to be getting hot from feel, the bottom much cooler, but my needle wouldn't ever go over a little below half. I since got a hold of a guy I know who's a certified Toyota mech and he told me that they like to run on the warmer side, about 200...it makes them more efficient, plus I have a 195* fan switch that rarely kicks on at the bottom of the radiator, about 10 inches down the line from the thermo. When doing this swap of course you want to match the senders with the gauges, but I've read nothing about the coolant sender other than "take your 3.4 sender out and put your 3.0 in". Made sense, but there seems to be an issue here. In my research the 92+ 3.0 senders to the 03 3.4 senders (and maybe further) share the same part # and is a 1/8 G.A.S. fitting. The 88-91 3.0 had the larger style threads (M16x1.5 I think), but they still share the single blade terminal. Both are gauge senders, not for ECU. Here's the thing that got me a little worried and confirmed (maybe) my beliefs. Somewhere between 91 & 92 Toyota must have changed resistance values. I verified this with 3 gauges brand new and a mulit-meter. The resistance at room temp for the larger (88-91) sender on the 2k ohm setting was 1.0xx. The value on the smaller 92+ was .5xx, nearly half the resistance. This might explain why my needle shot up to half and stopped, never goes higher, or is this thinking backwards. I'm thinking it's not seeing enough resistance to move further up the gauge. The senders were for an 88 3.0, a 95 3.0, and a 03 3.4. I hate to say it, but I'm guessing the people, including me, who did this swap with a 91 or earlier may be having the same issue and not getting accurate temps (makes me wonder how much higher the needle wanted to go?). It appears the only thing to do would be to tap the manifold for the larger, correct gauge for the year, do another "jamb nut mod" on the top of the radiator near where the coolant exits, find another sender with the right threads and resistance value, or get into the board and solder a resistor somewhere...but where? Went to RadioShack and they had the 1/4w 470ohm resistors that would give the newer style sender a similar value if I only knew where to put it. Could I run this inline with the sender wire itself? Am I nuts here or has anybody else come across this issue? Also, here is some service data for the circuit board values for the temp gauge, for both an 88 3.0 and a 03 3.4 clipped from the respective FSMs..

vital22re

iTrader: (2)

sounds normal to me... My swap runs just before half too..

77RogueRunner

So I'm neurotic (quite possibly)? I remember when I had my old 2.8 Supra swap, I could watch the gauge slowly go up to normal then drop down when the thermostat popped and the cool stuff pumped in, then raise back up to the norm under normal driving conditions, go a little higher when it was hot and I was at a stop light. I'd come home turn it to IGN 15 min later and it was a little over half which is what I expected being the coolant is stagnant and absorbing the heat. 45 min later, it was at maybe 1/4. Not with this setup though, just goes to right below half (quickly), stays there, come out 45 min later after shutting the engine off and it is still the same...right below half, granted my upper is still pretty hot. Not only that but the different resistance values for the sender years and style and different resistance values for the years in gauges would make me think there is something there that's not totally right. Gonna try to track down a 92 FSM and verify it is the same values (or not) as the 03 Taco, and maybe a 90 or 91 FSM to verify with the 88 3.0 gauge. If anybody has access to this info post it up...

Here's some more stuff I just found.
The sender change happens 8/92. So after that date you have the 1/8 GAS, before that you have the M16x1.5, per this link which I have found very helpful...

http://www.tridon.com.au/Products/Pr...5&G=483&P=2012

also the parts finder selection is nice for vehicle specific stuff...