Educate me on SI Boards

[CompleteCustoms]

I have an '86 325 (m20b27) that is having some overheating issues. Based on what I have read, it seems that one of the possible causes could be the SI board. I have never heard of an SI board before and am not really sure what it does. Again, based on what I have read, it seems that it just monitors your service intervals. Is this correct? How would this effect the cooling system? Does it just cause the temp gauge to work inaccurately?

Thanks

[e30slidewayz]

Is the car actually running hot or does your temp gauge just say it's running hot? The SI board is part of your dash cluster and controls the dash lights, tach, temp gauge, fuel gauge, etc. It wouldn't have any effect on your cooling system.

[reelizmpro]

Verify that you are indeed overheating if the gauge is inaccurate the find out why. If it's jumpy, chances are it's a bad ground in back of the gauge. There's a nut that needs to be tightened to make better contact. The SI board cannot cause you to overheat.

[CompleteCustoms]

I think the car is actually overheating, the gauge moves very linearly. How do I confirm this?

I think I need to clarify a little, I might not have been very clear. I know that a faulty SI board wouldn't cause it to overheat, it would just cause the gauge to read that it is overheating, which may lead you to think it is overheating.

I am more interested in knowing what the SI board does.

[reelizmpro]

It calibrates the gauges, collects information and adjusts the service interval according to your driving style.

[dnguyen1963]

If your temp gauge start to jump around erratically then it is most likely that the NiCd batteries are dead or your SI board is toasted. The SI board controls the temp and tach/eco gauges in addition to keeping track of service intervals. Take a temp reading of your coolant to confirm that you are not overheating. You can also remove the SI board from the cluster to see if any corrosion is present. Another critical thing to do is to make sure your ground nuts are tight and clean.

[FLG]

Where does the gauge actually read? Some peoples definition of overheating is different than others.

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[Gregs///M]

Signal for temperature gauge runs through the SI board. Use an infrared temperature probe to verify temp at the thermostat housing. Normal temp should be around 190F.

Your temp gauge should maintain at middle at normal operating temp. If it does not, could be nuts behind gauge, grounding lugs above brake pedal, or Engine to Chassis ground cable on drivers side of engine bay. When the engine to chassis cable becomes corroded, oily, or damaged or loose it will give you inaccurate gauge feedback among other things such as no start when hot.

I have spare SI boards, if you need one. PM me.

[dnguyen1963]

Where does the gauge actually read? Some peoples definition of overheating is different than others.

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190F is a tad below middle in the gauge. SI board related problem is seen when the needle starts normal then suddenly jumps to 3/4 and sometimes into the red zone...very erratic to its location.

[TurboJake]

Also, 99% of the time other gauges are affected by a bad SI board. Especially the tach and Econometer.

[CompleteCustoms]

I have spare SI boards, if you need one. PM me.

I'm going to look into this weekend, I will definitely PM you if I need one.

[CompleteCustoms]

Where does the gauge actually read? Some peoples definition of overheating is different than others.

Typically it reads a little over the first mark, maybe up to the middle mark, but that's it. When I first noticed it reading hot, it was damn near the red. After changing the thermostat, I let it sit and idle and it started creeping towards 3/4 before I turned it off.

[CompleteCustoms]

If your temp gauge start to jump around erratically then it is most likely that the NiCd batteries are dead or your SI board is toasted. The SI board controls the temp and tach/eco gauges in addition to keeping track of service intervals. Take a temp reading of your coolant to confirm that you are not overheating. You can also remove the SI board from the cluster to see if any corrosion is present. Another critical thing to do is to make sure your ground nuts are tight and clean.

Thanks that helps a lot. All of the other gauges work fine, and the temp gauge isn't erratic, it just steadily climbs.

[jlevie]

Typically it reads a little over the first mark, maybe up to the middle mark, but that's it. When I first noticed it reading hot, it was damn near the red. After changing the thermostat, I let it sit and idle and it started creeping towards 3/4 before I turned it off.

That sounds like a bad fan clutch, perhaps aggravated by a failure to fully bleed the cooling system.

[Gregs///M]

Yeah most likely air in the system still. Bleed, bleed, and rebleed. Double check your gauge with infrared temp or some sort of secondary temp sensor.