What is a CTO

[bchesley]

What does CTO stand for and what is there actual purpose?? Can they go bad?

[Ralph]

It's a mechanical switch and stands for "Coolant Temperature Override." What happens is the engine coolant runs past the CTO, and as the coolant heats and increases pressure in the cooling system a plunger in the CTO is forced upward and closes off one vacuum outlet and opens another. An important CTO in a FSJ is used to alter vacuum to the distributor.

[Bob Barry]

Ralph covered the first part of your question; in answer to the second part, yes, they can go bad, becoming a source of annoying vacuum leaks.

Replacements are readily available; just about everybody but Jeep calls these TVS's (Thermostatic Vacuum Switches). I've got a cross-reference chart in my tech pages (link below) that can help you find aftermarket replacements.

[bchesley]

That is exactly what I needed. Thanks. I also have a two port round type device. It is over by the thermostat housing. It is loose and not attached to anything. What is it? TIA.

[<Puvong>]

That's right Dr. Bob has a good cross reference chart to the alternative after market replacement. However, the 2-port CTO might have many different temperature range and sometimes the color code won't match neither and hopefully the guy at the counter will understand what you're looking for. You need to ask them if they have a replacement "TVS or CTO" valve identification chart and the chart is usualy inside the package. Then try to match the original CTO color code, but make sure the temperature is correct.

[Bob Barry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by bchesley:
That is exactly what I needed. Thanks. I also have a two port round type device. It is over by the thermostat housing. It is loose and not attached to anything. What is it? TIA.<HR></BLOCKQUOTE>

Ah, now that's your NLVRV (Non-Linear Vacuum Relay Valve). Seriously. I know it sounds made-up like Blinker Fluid and a Johnson Rod, but what it does is keep the vacuum signal to the distributor within a given range (I believe at least 7" of vacuum) by pulling from both ported and manifold sources. It should have three ports, btw: two source and one feed.

I know I did away with mine on my '88 as one potential source of vacuum leaks, and never noticed a performance loss or gain.

[bchesley]

I went to your site to check out the vacuum diagram and noticed that one of the 89 diagrams only has two CTO's but the 83-84 & the other 89 has three. My 89 has three so what gives?? This weekend I am replacing all of the vacuum lines and CTO's so if I don't have to buy one and can plug a hole that would be great. If you got rid of your NLVRV where are you getting vacuum for your distributor?

[Bob Barry]

The regular-duty cooling system used two CTO's; a low-temp spark unit and a dual CTO for the TAC and the EGR (EGR only in earlier years).

The heavy-duty cooling system (which is what A/C-equipped trucks, and hence almost all GW's) used three CTO's: a low-temp and a high-temp spark unit, and a dual CTO for the TAC and the EGR.