Guys, i know some of you have gotten (or will get) into a situation where time dictates that you just buy a new UIM from the jobber.

I received four junkyard UIMs from Boosty yesterday and get a chance to take a look at them closely today. Two had failed; two hadn't.

I noticed that BOTH UIMs that had failed had the coolant passages into the throttle body section occluded about 50% by plastic casting flash. The UIMs that were intact had very little casting flash in the passages.

I know that this is only a sample of four, but it occurs to me that if you're going to do a stock replacement, it'* worthwhile to inspect the coolant passages for casting flash, and if there'* a lot, run a 3/8" drill bit through the passage to remove it.

gently, of course.

I'm going to start keeping track of this as additional UIMs come in for sleeving. May be nothing, but on the other hand, intuitively, it could be the problem, eh?

I can't see that causing any issues unless the flash prevented the gasket from sealing. Many bypass this flow anyway (or rather block it) as it'* a parallel path from the front to the rear head, not Series for any other flow path.

It IS a quality issue though. I won't argue that point.

Will, no gasket sealing issues, but coolant flow is probably decreased. If we assume that the coolant keeps the area around the EGR passage at a reasonable temperature, and that coolant flow is impeded, perhaps a lesser coolant flow is the straw that breaks the camel'* back.

That was my thinking, anyway, again noting a sample of four is not much. I'll keep my eye on them.

Good point, Bob.

My understanding is that coolant flow actually has a heating effect, not cooling. I can understand the flow being necessary around the EGR stovepipe, but personally don't see an issue with restricted flow to the TB unless that flow is a series path to the EGR area.

Can we confirm whether the flow is series or parallel? I'm not as familiar with the L36 UIM as some of you guys.

The reason coolant ends up in the intake is because the coolant passages are directly in the manifold on either side of the EGR pipe passage. Therefore when the EGR gets too hot, the UIM starts breaking down and cracking allowing coolant into the upper intake area.

With this coolant being there and the EGR area seeming to break down from heat, it is Bob'* theory that the coolant in the passages keep the EGR area of the UIM cooler than it would be w/o coolant flowing.

While recently there have been many conversations about what the actual reason for having coolant flow into the throttle body may be...it could serve a dual purpose. To keep from icing in the winter (which seems overly cautious and unnecessary) and a cooling effect for the EGR area of the UIM.

Right, that'* understood, but is it possible to allow the coolant to work on the EGR area, and bypass it from the TB?

Not easily. The two coolant bores around the big EGR bore in the UIM do not communicate with each other in the UIM. Where they exit the UIM, those passages are irregularly shaped, with their outside edges defined in part by the throttle body gasket.

The flashing your seeing on the failures could just be a particular lot/year mfg. run that had a slightly different raw material that was suseptable to breakdown.
What are the date codes of these two?