Engine and Exhaust Manifold Temperatures - '99 Mercruiser 5.0L TKS - Alpha1 Gen II

[bvetter]

Hoping to get some info/advice from the Mercruiser guru's out there.
Engine is a 1999 5.0L TKS, with Alpha 1 Gen 2.
Impeller replaced just last week.

Had the boat on the water yesterday for the first time this season. After running it a while (idling and cruising), I opened the engine compartment to look around and "it seemed to me" the engine and exhaust manifolds felt hotter than I remember in past seasons. From what I remember, the exhaust manifolds always felt cold or slightly warm to the touch, even after cruising around, and the engine compartment was always just warm, not really hot. Yesterday on the lake, the port side was nice and cool (along with water supply hose to it), however the stbd side was hot to the touch (including the water supply hose to it). When I say hot, I mean I could put my hand on the top of the manifold and hold it there for 5s or so before I had to take it off.

Got back from the lake and put the muffs on in the driveway and got the engine up to temp, then bumped up the RPM's to 1200 and let it warm up further. The temps on the manifold and hoses felt exactly the same as on the lake. No difference.

The engine temp seems to be regulating properly, no overheating as far as I can tell. The temp gauge climbs steadily to operating temp (approx. 160F), then levels out.
Here is a pic of the thermostat housing, with the various hoses labelled.



?A? ? Water inlet from impeller
?B? ? Supply to port exhaust manifold
?C? ? Supply to stbd exhaust manifold
?D? ? Recirc supply to engine water pump

Here are some of the tests I did in the driveway:

1. Removed t-stat housing and inspected, all looks ok, no blockages as far as I can see.
2. Removed t-stat and tested as per SELOC manual in pot of hot water with a thermometer. Opens and closes as expected. Thermostat rating is 160F.
3. Engine off, removed water inlet hose (A) from t-stat housing, directed into 5 gallon pail. With muffs on the outdrive and water turned on, started engine and set to idle. Water flow started coming out of hose after about 5 seconds or so. Rev?d up to about 1000RPM, water flow increased to a pretty good rate. Ie: water flow proportional to engine speed. Only ran for about 30 seconds total for this test.
4. Engine off, removed supply hose to port exhaust manifold (B). Connected it to a garden hose and turned on water, good flow coming out of port side exhaust hole behind transom plate.
5. Engine off, removed supply hose to stbd exhaust manifold (C). Connected it to a garden hose and turned on water, good flow coming out of stbd side exhaust hole behind transom plate.

From the testing, seems like there are no blockages in any of the cooling circuits, t-stat appears to be working properly and engine is regulating temperature. I don?t have an IR temperature gun, so don?t know exactly what the temperatures were of the various components. Just going off of feel.

SO, is what I am seeing ?normal?? Is it normal to see the stbd exhaust manifold hotter than port side?

 

[Bondo]

SO, is what I am seeing ?normal?? Is it normal to see the stbd exhaust manifold hotter than port side?

Ayuh,.... Both sides are rarely to never the same,....

How long can you hold yer hand in 160? water,..?? Not very long I suspect,....

 

[bvetter]

Ayuh,.... Both sides are rarely to never the same,....

How long can you hold yer hand in 160? water,..?? Not very long I suspect,....

Haha, good point. I've never tried. hwell:

My concern was that there was such a difference between the two manifolds. I guess I would have expected them to be roughly the same. I just noticed there is a tube between the stbd exhaust manifold and intake manifold, the tube is covered in a black sheath (you can see it in the above photo). Is that a coolant line or exhaust gas recirc of some sort?

 

[bvetter]

Anyone know what this tube is between the stbd side exhaust manifold and intake manifold? Is it a coolant (water) line or exhaust gas line? Parts lookup diagrams are calling it an exhaust tube but that doesn't seem to help much....

 

[bvetter]

Decided to take some engine temperature measurements tonight. Used an IR temperature gun for the recordings, every half minute, during warm up at 650RPM and at a few higher RPMs. I'm thinking everything looks normal, but if someone could confirm my numbers that would be great. Not sure how the table is going to paste from Excel (might have to scroll to the right to see the entire table, it's quite lengthy), hopefully it looks OK. All temperatures are in degrees F.

First, here is a pic of the measurement locations.



Here is the measurement data in tabular format:

	Time (Minutes)	0.0	0.5	1.0	1.5	2.0	2.5	3.0	3.5	4.0	4.5	5.0	5.5	6.0	6.5	7.0	7.5	8.0	8.5	9.0	9.5	10.0	10.5	11.0	11.5	12.0	12.5	13.0	13.5	14.0	14.5	15.0	15.5	16.0	16.5	17.0	17.5	18.0	18.5	19.0	19.5	20.0	20.5	21.0	21.5	22.0	22.5	23.0	23.5	24.0	24.5	25.0	25.5	26.0	26.5	27.0	27.5	28.0	28.5	29.0	29.5	30.0	30.5	31.0	31.5	32.0	32.5	33.0	33.5	34.0	34.5	35.0
	Engine Speed (RPM)	0	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	650	1000	1000	1000	1000	1000	1000	1000	1000	1000	1000	1400	1400	1400	1400	1400	1400	1400	1400	1400	1400	1800	1800	1800	1800	1800	1800	1800	1800	1800	1800	650	650	650	650	650	650	650	650	650	650	650
A	Fresh Water Supply Hose to Port Exhaust	76	72	70	68	66	65	64	64	64	63	63	64	64	64	64	64	64	64	66	65	65	66	66	65	65	66	66	66	66	67	67	66	66	66	66	67	66	67	67	67	69	68	70	69	69	71	71	70	71	70	71	72	73	73	74	74	75	74	75	75	73	74	73	72	71	69	68	68	68	68	68
B	Fresh Water Supply Hose to Stbd Exhaust	76	71	67	65	63	63	63	63	63	63	63	63	63	65	65	65	67	83	87	81	76	76	77	79	79	80	81	81	81	82	82	85	88	90	90	92	91	92	93	94	95	96	97	99	101	102	100	102	101	102	103	105	107	108	109	110	111	112	111	112	110	105	101	94	89	86	84	83	83	83	83
C	Recirc Hose to Water Pump	76	76	76	76	78	78	79	81	81	83	85	89	91	94	98	102	106	107	106	108	109	112	112	112	113	114	115	115	116	117	116	120	125	128	130	133	133	136	136	135	137	138	138	138	138	138	138	139	139	138	139	139	141	139	139	140	140	141	140	139	140	139	136	133	131	131	130	128	128	128	127
D	Top of T-Stat Housing	76	60	60	60	60	60	60	61	61	61	61	62	62	62	64	65	132	117	73	69	71	73	78	77	76	76	77	77	75	75	90	87	92	96	92	93	95	90	97	96	107	105	105	108	112	111	108	111	113	114	116	117	118	121	121	121	123	122	121	122	97	105	86	76	77	77	75	76	77	75	77
E	Base of T-Stat Housing (Intake Manifold)	76	80	87	95	102	109	115	122	136	141	144	149	152	155	160	162	165	156	149	152	157	158	159	160	158	159	159	159	159	161	156	155	156	157	156	157	157	158	157	157	157	158	158	158	159	158	159	158	158	159	158	159	159	159	159	159	160	160	160	160	164	162	159	157	158	158	159	159	158	159	159
F	Top of Port Exhaust Riser	76	77	77	77	77	77	77	79	80	81	81	81	82	83	82	83	83	85	87	86	86	86	87	88	89	89	91	93	93	94	87	82	79	79	79	79	79	79	79	78	80	82	84	83	86	86	85	86	85	86	87	90	93	96	98	99	101	100	102	101	102	103	104	104	105	104	104	102	101	101	96
G	Top of Stbd Exhaust Riser	76	74	71	70	70	70	69	70	69	70	70	70	70	71	72	71	93	104	94	85	82	82	85	86	87	88	87	88	88	88	92	97	99	101	102	102	104	104	104	105	107	109	111	111	112	113	114	113	113	113	117	121	124	125	126	127	128	128	129	127	122	112	101	92	89	87	87	87	86	87	86

And the measurement data in a graph:





The engine temp at the base of the thermostat slightly overshot the 160F rating at about the 8.0 minute mark (which is normal from what I understand), then levelled off once the thermostat opened up. It maintained 160F very nicely throughout the testing so that's good news. What's puzzling, is how the two supply hoses going from the t-stat housing to each exhaust header had quite different temperatures once everything warmed up, even though they are sourced from the exact same chamber in the t-stat housing. Weird. I suspect it has something to do with the tube that runs between the stbd exhaust header and the intake manifold which I noted in my last post (must have hot engine water circulating in that line).

Anyways, if someone has taken measurements in the past, it would be great to compare against these numbers. I've seen a few posts recently by others regarding engine temperature issues, so hopefully at the very least this data will help others out.

Cheers,

Brandon